Mixing
Printing a comma-separated list in C++
Clash Royale CLAN TAG#URR8PPP
up vote
1
down vote
favorite
A well-formed comma-separated list has commas after all but the last element. This means that when dealing with these lists, the comma has to be dealt with on all but the last iteration. This is how I do things currently:
for (auto e = vec.cbegin(); e != vec.cend(); ++e)
// code that has to be executed for every element
std::cout << *e;
if (e != vec.cend() - 1)
// code that must not be executed for the last element
std::cout << ", ";
There are five instances of the above pattern in the project that I'm working on. I feel like there might be a more elegant way of doing this. An alternative that I've come up with is this:
// infinite loop if vec is empty
if (!vec.empty())
for (auto e = vec.cbegin(); e != vec.cend() - 1; ++e)
// code that has to be executed for every element
std::cout << *e;
// code that must not be executed for the last element
std::cout << ", ";
// code that has to be executed for every element
std::cout << vec.back();
This alternative is slightly faster because there isn't an if in the body but that's not a big deal. The if is true for all but the last iteration so the branch predictor will probably only miss on the last iteration. I also have to repeat code that has to be executed for every element which means that I need to hoist that into a function.
The first snippet is the best that I can come up with but I feel like this could be done better. Note that writing to std::cout is just an example.
c++ formatting vectors c++17 iteration
edited 40 mins ago
200_success
126k14147409
asked 10 hours ago
Kerndog73
446213
 |Â
show 4 more comments
up vote
1
down vote
favorite
A well-formed comma-separated list has commas after all but the last element. This means that when dealing with these lists, the comma has to be dealt with on all but the last iteration. This is how I do things currently:
for (auto e = vec.cbegin(); e != vec.cend(); ++e)
// code that has to be executed for every element
std::cout << *e;
if (e != vec.cend() - 1)
// code that must not be executed for the last element
std::cout << ", ";
There are five instances of the above pattern in the project that I'm working on. I feel like there might be a more elegant way of doing this. An alternative that I've come up with is this:
// infinite loop if vec is empty
if (!vec.empty())
for (auto e = vec.cbegin(); e != vec.cend() - 1; ++e)
// code that has to be executed for every element
std::cout << *e;
// code that must not be executed for the last element
std::cout << ", ";
// code that has to be executed for every element
std::cout << vec.back();
This alternative is slightly faster because there isn't an if in the body but that's not a big deal. The if is true for all but the last iteration so the branch predictor will probably only miss on the last iteration. I also have to repeat code that has to be executed for every element which means that I need to hoist that into a function.
The first snippet is the best that I can come up with but I feel like this could be done better. Note that writing to std::cout is just an example.
c++ formatting vectors c++17 iteration
edited 40 mins ago
200_success
126k14147409
asked 10 hours ago
Kerndog73
446213
2
You're implementing anostream_joiner- is this reinventing-the-wheel, or do you need something for straight C++17 withoutstd::experimental?
– Toby Speight
6 hours ago
1
So this is not the actual code you have written or are maintaining? Clearly off-topic, I'm afraid.
– Toby Speight
6 hours ago
2
@Kerndog73, if you're talking about me, I'm not intending to be hostile, and apologies if you perceive things that way. I think you may well be able to salvage an on-topic question from this, and there's some very worthwhile observations I'd be able to make if I could see an actual context. It really helps to have compilable code - it's worth writing a smallmain()to exercise a function you've made for your project, for example, and you should definitely include the headers and/or definitions you use. I want this to be a good, on-topic question, and it's frustrating that it's not (yet).
– Toby Speight
5 hours ago
1
@TobySpeight It's OK. I'm sorry for saying that. The problem is that I was looking for advice about a pattern that is repeated multiple times in different contexts. That's why I wrote code to print a vector. This question is off-topic.
– Kerndog73
5 hours ago
2
@Kerndog73 I’m honestly confused by the rules as well. This question might be better suited for softwareengineering.stackexchange.com (what a mouthful, that URL). But I’m not absolutely sure it is, and I believe there should be a room for such a question somewhere.
– Konrad Rudolph
4 hours ago
 |Â
show 4 more comments
up vote
1
down vote
favorite
up vote
1
down vote
favorite
A well-formed comma-separated list has commas after all but the last element. This means that when dealing with these lists, the comma has to be dealt with on all but the last iteration. This is how I do things currently:
for (auto e = vec.cbegin(); e != vec.cend(); ++e)
// code that has to be executed for every element
std::cout << *e;
if (e != vec.cend() - 1)
// code that must not be executed for the last element
std::cout << ", ";
There are five instances of the above pattern in the project that I'm working on. I feel like there might be a more elegant way of doing this. An alternative that I've come up with is this:
// infinite loop if vec is empty
if (!vec.empty())
for (auto e = vec.cbegin(); e != vec.cend() - 1; ++e)
// code that has to be executed for every element
std::cout << *e;
// code that must not be executed for the last element
std::cout << ", ";
// code that has to be executed for every element
std::cout << vec.back();
This alternative is slightly faster because there isn't an if in the body but that's not a big deal. The if is true for all but the last iteration so the branch predictor will probably only miss on the last iteration. I also have to repeat code that has to be executed for every element which means that I need to hoist that into a function.
The first snippet is the best that I can come up with but I feel like this could be done better. Note that writing to std::cout is just an example.
c++ formatting vectors c++17 iteration
edited 40 mins ago
200_success
126k14147409
asked 10 hours ago
Kerndog73
446213
A well-formed comma-separated list has commas after all but the last element. This means that when dealing with these lists, the comma has to be dealt with on all but the last iteration. This is how I do things currently:
for (auto e = vec.cbegin(); e != vec.cend(); ++e)
// code that has to be executed for every element
std::cout << *e;
if (e != vec.cend() - 1)
// code that must not be executed for the last element
std::cout << ", ";
There are five instances of the above pattern in the project that I'm working on. I feel like there might be a more elegant way of doing this. An alternative that I've come up with is this:
// infinite loop if vec is empty
if (!vec.empty())
for (auto e = vec.cbegin(); e != vec.cend() - 1; ++e)
// code that has to be executed for every element
std::cout << *e;
// code that must not be executed for the last element
std::cout << ", ";
// code that has to be executed for every element
std::cout << vec.back();
This alternative is slightly faster because there isn't an if in the body but that's not a big deal. The if is true for all but the last iteration so the branch predictor will probably only miss on the last iteration. I also have to repeat code that has to be executed for every element which means that I need to hoist that into a function.
The first snippet is the best that I can come up with but I feel like this could be done better. Note that writing to std::cout is just an example.
c++ formatting vectors c++17 iteration
c++ formatting vectors c++17 iteration
edited 40 mins ago
200_success
126k14147409
asked 10 hours ago
Kerndog73
446213
edited 40 mins ago
200_success
126k14147409
asked 10 hours ago
Kerndog73
446213
edited 40 mins ago
200_success
126k14147409
edited 40 mins ago
200_success
126k14147409
edited 40 mins ago
200_success
126k14147409
126k14147409
asked 10 hours ago
Kerndog73
446213
asked 10 hours ago
Kerndog73
446213
asked 10 hours ago
Kerndog73
446213
446213
2
You're implementing anostream_joiner- is this reinventing-the-wheel, or do you need something for straight C++17 withoutstd::experimental?
– Toby Speight
6 hours ago
1
So this is not the actual code you have written or are maintaining? Clearly off-topic, I'm afraid.
– Toby Speight
6 hours ago
2
@Kerndog73, if you're talking about me, I'm not intending to be hostile, and apologies if you perceive things that way. I think you may well be able to salvage an on-topic question from this, and there's some very worthwhile observations I'd be able to make if I could see an actual context. It really helps to have compilable code - it's worth writing a smallmain()to exercise a function you've made for your project, for example, and you should definitely include the headers and/or definitions you use. I want this to be a good, on-topic question, and it's frustrating that it's not (yet).
– Toby Speight
5 hours ago
1
@TobySpeight It's OK. I'm sorry for saying that. The problem is that I was looking for advice about a pattern that is repeated multiple times in different contexts. That's why I wrote code to print a vector. This question is off-topic.
– Kerndog73
5 hours ago
2
@Kerndog73 I’m honestly confused by the rules as well. This question might be better suited for softwareengineering.stackexchange.com (what a mouthful, that URL). But I’m not absolutely sure it is, and I believe there should be a room for such a question somewhere.
– Konrad Rudolph
4 hours ago
 |Â
show 4 more comments
2
You're implementing anostream_joiner- is this reinventing-the-wheel, or do you need something for straight C++17 withoutstd::experimental?
– Toby Speight
6 hours ago
1
So this is not the actual code you have written or are maintaining? Clearly off-topic, I'm afraid.
– Toby Speight
6 hours ago
2
@Kerndog73, if you're talking about me, I'm not intending to be hostile, and apologies if you perceive things that way. I think you may well be able to salvage an on-topic question from this, and there's some very worthwhile observations I'd be able to make if I could see an actual context. It really helps to have compilable code - it's worth writing a smallmain()to exercise a function you've made for your project, for example, and you should definitely include the headers and/or definitions you use. I want this to be a good, on-topic question, and it's frustrating that it's not (yet).
– Toby Speight
5 hours ago
1
@TobySpeight It's OK. I'm sorry for saying that. The problem is that I was looking for advice about a pattern that is repeated multiple times in different contexts. That's why I wrote code to print a vector. This question is off-topic.
– Kerndog73
5 hours ago
2
@Kerndog73 I’m honestly confused by the rules as well. This question might be better suited for softwareengineering.stackexchange.com (what a mouthful, that URL). But I’m not absolutely sure it is, and I believe there should be a room for such a question somewhere.
– Konrad Rudolph
4 hours ago
2
2
You're implementing an
ostream_joiner - is this reinventing-the-wheel, or do you need something for straight C++17 without std::experimental?– Toby Speight
6 hours ago
You're implementing an
ostream_joiner - is this reinventing-the-wheel, or do you need something for straight C++17 without std::experimental?– Toby Speight
6 hours ago
1
1
So this is not the actual code you have written or are maintaining? Clearly off-topic, I'm afraid.
– Toby Speight
6 hours ago
So this is not the actual code you have written or are maintaining? Clearly off-topic, I'm afraid.
– Toby Speight
6 hours ago
2
2
@Kerndog73, if you're talking about me, I'm not intending to be hostile, and apologies if you perceive things that way. I think you may well be able to salvage an on-topic question from this, and there's some very worthwhile observations I'd be able to make if I could see an actual context. It really helps to have compilable code - it's worth writing a small
main() to exercise a function you've made for your project, for example, and you should definitely include the headers and/or definitions you use. I want this to be a good, on-topic question, and it's frustrating that it's not (yet).– Toby Speight
5 hours ago
@Kerndog73, if you're talking about me, I'm not intending to be hostile, and apologies if you perceive things that way. I think you may well be able to salvage an on-topic question from this, and there's some very worthwhile observations I'd be able to make if I could see an actual context. It really helps to have compilable code - it's worth writing a small
main() to exercise a function you've made for your project, for example, and you should definitely include the headers and/or definitions you use. I want this to be a good, on-topic question, and it's frustrating that it's not (yet).– Toby Speight
5 hours ago
1
1
@TobySpeight It's OK. I'm sorry for saying that. The problem is that I was looking for advice about a pattern that is repeated multiple times in different contexts. That's why I wrote code to print a vector. This question is off-topic.
– Kerndog73
5 hours ago
@TobySpeight It's OK. I'm sorry for saying that. The problem is that I was looking for advice about a pattern that is repeated multiple times in different contexts. That's why I wrote code to print a vector. This question is off-topic.
– Kerndog73
5 hours ago
2
2
@Kerndog73 I’m honestly confused by the rules as well. This question might be better suited for softwareengineering.stackexchange.com (what a mouthful, that URL). But I’m not absolutely sure it is, and I believe there should be a room for such a question somewhere.
– Konrad Rudolph
4 hours ago
@Kerndog73 I’m honestly confused by the rules as well. This question might be better suited for softwareengineering.stackexchange.com (what a mouthful, that URL). But I’m not absolutely sure it is, and I believe there should be a room for such a question somewhere.
– Konrad Rudolph
4 hours ago
 |Â
show 4 more comments
5 Answers
5
active
oldest
votes
up vote
9
down vote
accepted
If you are just doing a single-shot printing of a container, just print the first element and then print delim-value pairs. This reduces the iterator requirements to being equality comparable, dereferenceable, and incrementable.
if (!vec.empty()) // invert to return immediately if this is a function
auto first = vec.cbegin();
std::cout << *first;
while (vec.cend() != ++first)
std::cout << ", " << *first;
There is also a stateful approach that reduces the operation strength from branching on whether to print the delimiter to a pointer assignment.
auto actual_delim = ", ";
auto delim = "";
for (const auto& elem : vec)
std::cout << delim << elem;
delim = actual_delim;
See infix_iterator where this stateful approach is used.
answered 8 hours ago
Snowhawk
4,87411027
As mentioned in my answer, this approach has the distinct advantage of duplicating the logic of the loop body.
– Konrad Rudolph
4 hours ago
Second version is much more appealing, as we don't lose range-basedfor(and you can set a function pointer or plainboolvariable instead of a string-pointer if necessary). In a worst case, we could test&elem == &vec.back()if we can't make the first element have the variant behaviour (e.g. joining a list with" and "as the final separator).
– Toby Speight
22 mins ago
add a comment |Â
up vote
4
down vote
I'm not sure that elegance should be your first concern here, because the algorithm should be very simple and the code short however you write them.
I/O operations will have a much greater impact on performance than the lay-out of your loop, so you shouldn't worry too much about speed either.
Generality, I believe, is paramount in this case. That's why I see vec.cend() - 1 as the main short-coming of your proposal, because it restricts your algorithm to at least bidirectional iterators, when your goal can be easily achieved for any kind of iterator.
Here's what I would consider better:
#include <iostream>
#include <vector>
template <typename Container, typename Separator> // any container is acceptable...
void pretty_print(const Container& c, const Separator& s)
std::cout << '';
auto it = std::begin(c); // ... even arrays
if (it != std::end(c)) do
std::cout << *it;
if (++it == std::end(c)) break; // that way you don't need to decrement the iterator
std::cout << s;
while (true);
std::cout << '';
answered 9 hours ago
papagaga
3,694221
I did mention that writing tostd::coutwas just an example but I do like that this works with forward iterators.
– Kerndog73
9 hours ago
I think I have to agree with Calak (answer below): this variant is decidedly less readable than others. But it would help to make it equivalent to what OP is doing to have a direct comparison (i.e. remove the printing of the braces).
– Konrad Rudolph
7 hours ago
add a comment |Â
up vote
1
down vote
I always just use an additional variable:
auto first= true;
for (auto const& x : list)
if (first) first = false; else separator(x);
action(x);
In your case, separator(x) would be std::cout << ", " (x isn’t actually used), and action(x) would be std::cout << x.
I normally abhor mutating variables inside a loop and try to use standard library algorithms on lambdas without side-effects instead. But in this case I believe having an additional boolean flag is simply the most economical, most readable solution.
This is also one of the very few cases (the only?) where I’m using a single-line if…else.
The advantage of this method is that you don’t have to duplicate action(x). Even if it’s just a single, simple expression, having such a duplication makes the logic disjointed and harder to follow.
The disadvantage is that the condition first has to be checked on every loop iteration. My suspicion is that the CPU’s branch predictor will handle this extremely well so it shouldn’t impact performance. Still, it’s conceptually irksome.
answered 8 hours ago
Konrad Rudolph
4,8911431
As always I’d love an explanation for downvotes.
– Konrad Rudolph
4 hours ago
add a comment |Â
up vote
1
down vote
We are getting closer to the off-topic "opinion-based" border
What's readable is a matter of taste. Honestly, i find the @papafaga version less fluent.
You also have the possibility to do the opposite of your second version, to put the particular case before the loop, I do it sometimes when the case is trivial.
template <typename Container, typename Separator>
void pretty_print4(const Container& c, const Separator& s)
if (c.empty()) return;
auto it = std::begin(c);
std::cout << *it;
std::advance(it,1);
while (it != std::end(c))
std::cout << s;
std::cout << *it;
std::advance(it,1);
If you talk about performance, I think all versions are worth. Without optimizations, some versions generate more instructions than others, but once in -O3, except one or two instructions, it's almost the same. After, if it really matters, you have to look at the machine code and benchmark.
answered 7 hours ago
Calak
1,0029
add a comment |Â
up vote
-1
down vote
I tried this:
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
template <typename Iterator, typename Char>
std::ostream& write_delim(std::ostream& out, Iterator iter, Iterator end, Char delim)
if (iter != end)
out << *iter++;
for (; iter != end; ++iter)
out << delim << *iter;
return out;
int main(int argc, char** argv)
int result = 0;
typedef std::vector<std::string> string_collection;
string_collection strings;
strings.push_back("alpha");
strings.push_back("beta");
strings.push_back("kappa");
strings.push_back("omega");
write_delim(std::cout, strings.begin(), strings.end(), ',') << std::endl;
write_delim(std::cout, strings.begin(), strings.end(), ", ") << std::endl;
return result;
Output results:
alpha,beta,kappa,omega
alpha, beta, kappa, omega
For me, this:
- Clearly communicates the point of the function, both in its name, and in how the code is written.
- Is generic enough to be used in many situations... notice how I can use either a single character or multiple characters between the strings.
- Works on older compilers.
- Works whether you're writing to a file, console, string, or some customized output stream.
Refinements to this might better communicate errors if you chose the wrong type of delimiter for your output.
answered 7 hours ago
Joseph Van Riper
111
New contributor
Joseph Van Riper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Welcome to Code Review! Please refrain from answering low-quality questions that are likely to get closed. Once, you've answered, that limits what can be done to improve the question, making it more likely that your efforts are wasted. It's better to wait until the question is properly ready before you answer!
– Toby Speight
6 hours ago
add a comment |Â
5 Answers
5
active
oldest
votes
5 Answers
5
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
9
down vote
accepted
If you are just doing a single-shot printing of a container, just print the first element and then print delim-value pairs. This reduces the iterator requirements to being equality comparable, dereferenceable, and incrementable.
if (!vec.empty()) // invert to return immediately if this is a function
auto first = vec.cbegin();
std::cout << *first;
while (vec.cend() != ++first)
std::cout << ", " << *first;
There is also a stateful approach that reduces the operation strength from branching on whether to print the delimiter to a pointer assignment.
auto actual_delim = ", ";
auto delim = "";
for (const auto& elem : vec)
std::cout << delim << elem;
delim = actual_delim;
See infix_iterator where this stateful approach is used.
answered 8 hours ago
Snowhawk
4,87411027
As mentioned in my answer, this approach has the distinct advantage of duplicating the logic of the loop body.
– Konrad Rudolph
4 hours ago
Second version is much more appealing, as we don't lose range-basedfor(and you can set a function pointer or plainboolvariable instead of a string-pointer if necessary). In a worst case, we could test&elem == &vec.back()if we can't make the first element have the variant behaviour (e.g. joining a list with" and "as the final separator).
– Toby Speight
22 mins ago
add a comment |Â
up vote
9
down vote
accepted
If you are just doing a single-shot printing of a container, just print the first element and then print delim-value pairs. This reduces the iterator requirements to being equality comparable, dereferenceable, and incrementable.
if (!vec.empty()) // invert to return immediately if this is a function
auto first = vec.cbegin();
std::cout << *first;
while (vec.cend() != ++first)
std::cout << ", " << *first;
There is also a stateful approach that reduces the operation strength from branching on whether to print the delimiter to a pointer assignment.
auto actual_delim = ", ";
auto delim = "";
for (const auto& elem : vec)
std::cout << delim << elem;
delim = actual_delim;
See infix_iterator where this stateful approach is used.
answered 8 hours ago
Snowhawk
4,87411027
As mentioned in my answer, this approach has the distinct advantage of duplicating the logic of the loop body.
– Konrad Rudolph
4 hours ago
Second version is much more appealing, as we don't lose range-basedfor(and you can set a function pointer or plainboolvariable instead of a string-pointer if necessary). In a worst case, we could test&elem == &vec.back()if we can't make the first element have the variant behaviour (e.g. joining a list with" and "as the final separator).
– Toby Speight
22 mins ago
add a comment |Â
up vote
9
down vote
accepted
up vote
9
down vote
accepted
If you are just doing a single-shot printing of a container, just print the first element and then print delim-value pairs. This reduces the iterator requirements to being equality comparable, dereferenceable, and incrementable.
if (!vec.empty()) // invert to return immediately if this is a function
auto first = vec.cbegin();
std::cout << *first;
while (vec.cend() != ++first)
std::cout << ", " << *first;
There is also a stateful approach that reduces the operation strength from branching on whether to print the delimiter to a pointer assignment.
auto actual_delim = ", ";
auto delim = "";
for (const auto& elem : vec)
std::cout << delim << elem;
delim = actual_delim;
See infix_iterator where this stateful approach is used.
answered 8 hours ago
Snowhawk
4,87411027
If you are just doing a single-shot printing of a container, just print the first element and then print delim-value pairs. This reduces the iterator requirements to being equality comparable, dereferenceable, and incrementable.
if (!vec.empty()) // invert to return immediately if this is a function
auto first = vec.cbegin();
std::cout << *first;
while (vec.cend() != ++first)
std::cout << ", " << *first;
There is also a stateful approach that reduces the operation strength from branching on whether to print the delimiter to a pointer assignment.
auto actual_delim = ", ";
auto delim = "";
for (const auto& elem : vec)
std::cout << delim << elem;
delim = actual_delim;
See infix_iterator where this stateful approach is used.
answered 8 hours ago
Snowhawk
4,87411027
answered 8 hours ago
Snowhawk
4,87411027
answered 8 hours ago
Snowhawk
4,87411027
answered 8 hours ago
Snowhawk
4,87411027
4,87411027
As mentioned in my answer, this approach has the distinct advantage of duplicating the logic of the loop body.
– Konrad Rudolph
4 hours ago
Second version is much more appealing, as we don't lose range-basedfor(and you can set a function pointer or plainboolvariable instead of a string-pointer if necessary). In a worst case, we could test&elem == &vec.back()if we can't make the first element have the variant behaviour (e.g. joining a list with" and "as the final separator).
– Toby Speight
22 mins ago
add a comment |Â
As mentioned in my answer, this approach has the distinct advantage of duplicating the logic of the loop body.
– Konrad Rudolph
4 hours ago
Second version is much more appealing, as we don't lose range-basedfor(and you can set a function pointer or plainboolvariable instead of a string-pointer if necessary). In a worst case, we could test&elem == &vec.back()if we can't make the first element have the variant behaviour (e.g. joining a list with" and "as the final separator).
– Toby Speight
22 mins ago
As mentioned in my answer, this approach has the distinct advantage of duplicating the logic of the loop body.
– Konrad Rudolph
4 hours ago
As mentioned in my answer, this approach has the distinct advantage of duplicating the logic of the loop body.
– Konrad Rudolph
4 hours ago
Second version is much more appealing, as we don't lose range-based
for (and you can set a function pointer or plain bool variable instead of a string-pointer if necessary). In a worst case, we could test &elem == &vec.back() if we can't make the first element have the variant behaviour (e.g. joining a list with " and " as the final separator).– Toby Speight
22 mins ago
Second version is much more appealing, as we don't lose range-based
for (and you can set a function pointer or plain bool variable instead of a string-pointer if necessary). In a worst case, we could test &elem == &vec.back() if we can't make the first element have the variant behaviour (e.g. joining a list with " and " as the final separator).– Toby Speight
22 mins ago
add a comment |Â
up vote
4
down vote
I'm not sure that elegance should be your first concern here, because the algorithm should be very simple and the code short however you write them.
I/O operations will have a much greater impact on performance than the lay-out of your loop, so you shouldn't worry too much about speed either.
Generality, I believe, is paramount in this case. That's why I see vec.cend() - 1 as the main short-coming of your proposal, because it restricts your algorithm to at least bidirectional iterators, when your goal can be easily achieved for any kind of iterator.
Here's what I would consider better:
#include <iostream>
#include <vector>
template <typename Container, typename Separator> // any container is acceptable...
void pretty_print(const Container& c, const Separator& s)
std::cout << '';
auto it = std::begin(c); // ... even arrays
if (it != std::end(c)) do
std::cout << *it;
if (++it == std::end(c)) break; // that way you don't need to decrement the iterator
std::cout << s;
while (true);
std::cout << '';
answered 9 hours ago
papagaga
3,694221
I did mention that writing tostd::coutwas just an example but I do like that this works with forward iterators.
– Kerndog73
9 hours ago
I think I have to agree with Calak (answer below): this variant is decidedly less readable than others. But it would help to make it equivalent to what OP is doing to have a direct comparison (i.e. remove the printing of the braces).
– Konrad Rudolph
7 hours ago
add a comment |Â
up vote
4
down vote
I'm not sure that elegance should be your first concern here, because the algorithm should be very simple and the code short however you write them.
I/O operations will have a much greater impact on performance than the lay-out of your loop, so you shouldn't worry too much about speed either.
Generality, I believe, is paramount in this case. That's why I see vec.cend() - 1 as the main short-coming of your proposal, because it restricts your algorithm to at least bidirectional iterators, when your goal can be easily achieved for any kind of iterator.
Here's what I would consider better:
#include <iostream>
#include <vector>
template <typename Container, typename Separator> // any container is acceptable...
void pretty_print(const Container& c, const Separator& s)
std::cout << '';
auto it = std::begin(c); // ... even arrays
if (it != std::end(c)) do
std::cout << *it;
if (++it == std::end(c)) break; // that way you don't need to decrement the iterator
std::cout << s;
while (true);
std::cout << '';
answered 9 hours ago
papagaga
3,694221
I did mention that writing tostd::coutwas just an example but I do like that this works with forward iterators.
– Kerndog73
9 hours ago
I think I have to agree with Calak (answer below): this variant is decidedly less readable than others. But it would help to make it equivalent to what OP is doing to have a direct comparison (i.e. remove the printing of the braces).
– Konrad Rudolph
7 hours ago
add a comment |Â
up vote
4
down vote
up vote
4
down vote
I'm not sure that elegance should be your first concern here, because the algorithm should be very simple and the code short however you write them.
I/O operations will have a much greater impact on performance than the lay-out of your loop, so you shouldn't worry too much about speed either.
Generality, I believe, is paramount in this case. That's why I see vec.cend() - 1 as the main short-coming of your proposal, because it restricts your algorithm to at least bidirectional iterators, when your goal can be easily achieved for any kind of iterator.
Here's what I would consider better:
#include <iostream>
#include <vector>
template <typename Container, typename Separator> // any container is acceptable...
void pretty_print(const Container& c, const Separator& s)
std::cout << '';
auto it = std::begin(c); // ... even arrays
if (it != std::end(c)) do
std::cout << *it;
if (++it == std::end(c)) break; // that way you don't need to decrement the iterator
std::cout << s;
while (true);
std::cout << '';
answered 9 hours ago
papagaga
3,694221
I'm not sure that elegance should be your first concern here, because the algorithm should be very simple and the code short however you write them.
I/O operations will have a much greater impact on performance than the lay-out of your loop, so you shouldn't worry too much about speed either.
Generality, I believe, is paramount in this case. That's why I see vec.cend() - 1 as the main short-coming of your proposal, because it restricts your algorithm to at least bidirectional iterators, when your goal can be easily achieved for any kind of iterator.
Here's what I would consider better:
#include <iostream>
#include <vector>
template <typename Container, typename Separator> // any container is acceptable...
void pretty_print(const Container& c, const Separator& s)
std::cout << '';
auto it = std::begin(c); // ... even arrays
if (it != std::end(c)) do
std::cout << *it;
if (++it == std::end(c)) break; // that way you don't need to decrement the iterator
std::cout << s;
while (true);
std::cout << '';
answered 9 hours ago
papagaga
3,694221
answered 9 hours ago
papagaga
3,694221
answered 9 hours ago
papagaga
3,694221
answered 9 hours ago
papagaga
3,694221
3,694221
I did mention that writing tostd::coutwas just an example but I do like that this works with forward iterators.
– Kerndog73
9 hours ago
I think I have to agree with Calak (answer below): this variant is decidedly less readable than others. But it would help to make it equivalent to what OP is doing to have a direct comparison (i.e. remove the printing of the braces).
– Konrad Rudolph
7 hours ago
add a comment |Â
I did mention that writing tostd::coutwas just an example but I do like that this works with forward iterators.
– Kerndog73
9 hours ago
I think I have to agree with Calak (answer below): this variant is decidedly less readable than others. But it would help to make it equivalent to what OP is doing to have a direct comparison (i.e. remove the printing of the braces).
– Konrad Rudolph
7 hours ago
I did mention that writing to
std::cout was just an example but I do like that this works with forward iterators.– Kerndog73
9 hours ago
I did mention that writing to
std::cout was just an example but I do like that this works with forward iterators.– Kerndog73
9 hours ago
I think I have to agree with Calak (answer below): this variant is decidedly less readable than others. But it would help to make it equivalent to what OP is doing to have a direct comparison (i.e. remove the printing of the braces).
– Konrad Rudolph
7 hours ago
I think I have to agree with Calak (answer below): this variant is decidedly less readable than others. But it would help to make it equivalent to what OP is doing to have a direct comparison (i.e. remove the printing of the braces).
– Konrad Rudolph
7 hours ago
add a comment |Â
up vote
1
down vote
I always just use an additional variable:
auto first= true;
for (auto const& x : list)
if (first) first = false; else separator(x);
action(x);
In your case, separator(x) would be std::cout << ", " (x isn’t actually used), and action(x) would be std::cout << x.
I normally abhor mutating variables inside a loop and try to use standard library algorithms on lambdas without side-effects instead. But in this case I believe having an additional boolean flag is simply the most economical, most readable solution.
This is also one of the very few cases (the only?) where I’m using a single-line if…else.
The advantage of this method is that you don’t have to duplicate action(x). Even if it’s just a single, simple expression, having such a duplication makes the logic disjointed and harder to follow.
The disadvantage is that the condition first has to be checked on every loop iteration. My suspicion is that the CPU’s branch predictor will handle this extremely well so it shouldn’t impact performance. Still, it’s conceptually irksome.
answered 8 hours ago
Konrad Rudolph
4,8911431
As always I’d love an explanation for downvotes.
– Konrad Rudolph
4 hours ago
add a comment |Â
up vote
1
down vote
I always just use an additional variable:
auto first= true;
for (auto const& x : list)
if (first) first = false; else separator(x);
action(x);
In your case, separator(x) would be std::cout << ", " (x isn’t actually used), and action(x) would be std::cout << x.
I normally abhor mutating variables inside a loop and try to use standard library algorithms on lambdas without side-effects instead. But in this case I believe having an additional boolean flag is simply the most economical, most readable solution.
This is also one of the very few cases (the only?) where I’m using a single-line if…else.
The advantage of this method is that you don’t have to duplicate action(x). Even if it’s just a single, simple expression, having such a duplication makes the logic disjointed and harder to follow.
The disadvantage is that the condition first has to be checked on every loop iteration. My suspicion is that the CPU’s branch predictor will handle this extremely well so it shouldn’t impact performance. Still, it’s conceptually irksome.
answered 8 hours ago
Konrad Rudolph
4,8911431
As always I’d love an explanation for downvotes.
– Konrad Rudolph
4 hours ago
add a comment |Â
up vote
1
down vote
up vote
1
down vote
I always just use an additional variable:
auto first= true;
for (auto const& x : list)
if (first) first = false; else separator(x);
action(x);
In your case, separator(x) would be std::cout << ", " (x isn’t actually used), and action(x) would be std::cout << x.
I normally abhor mutating variables inside a loop and try to use standard library algorithms on lambdas without side-effects instead. But in this case I believe having an additional boolean flag is simply the most economical, most readable solution.
This is also one of the very few cases (the only?) where I’m using a single-line if…else.
The advantage of this method is that you don’t have to duplicate action(x). Even if it’s just a single, simple expression, having such a duplication makes the logic disjointed and harder to follow.
The disadvantage is that the condition first has to be checked on every loop iteration. My suspicion is that the CPU’s branch predictor will handle this extremely well so it shouldn’t impact performance. Still, it’s conceptually irksome.
answered 8 hours ago
Konrad Rudolph
4,8911431
I always just use an additional variable:
auto first= true;
for (auto const& x : list)
if (first) first = false; else separator(x);
action(x);
In your case, separator(x) would be std::cout << ", " (x isn’t actually used), and action(x) would be std::cout << x.
I normally abhor mutating variables inside a loop and try to use standard library algorithms on lambdas without side-effects instead. But in this case I believe having an additional boolean flag is simply the most economical, most readable solution.
This is also one of the very few cases (the only?) where I’m using a single-line if…else.
The advantage of this method is that you don’t have to duplicate action(x). Even if it’s just a single, simple expression, having such a duplication makes the logic disjointed and harder to follow.
The disadvantage is that the condition first has to be checked on every loop iteration. My suspicion is that the CPU’s branch predictor will handle this extremely well so it shouldn’t impact performance. Still, it’s conceptually irksome.
answered 8 hours ago
Konrad Rudolph
4,8911431
edited 8 hours ago
answered 8 hours ago
Konrad Rudolph
4,8911431
answered 8 hours ago
Konrad Rudolph
4,8911431
answered 8 hours ago
Konrad Rudolph
4,8911431
4,8911431
As always I’d love an explanation for downvotes.
– Konrad Rudolph
4 hours ago
add a comment |Â
As always I’d love an explanation for downvotes.
– Konrad Rudolph
4 hours ago
As always I’d love an explanation for downvotes.
– Konrad Rudolph
4 hours ago
As always I’d love an explanation for downvotes.
– Konrad Rudolph
4 hours ago
add a comment |Â
up vote
1
down vote
We are getting closer to the off-topic "opinion-based" border
What's readable is a matter of taste. Honestly, i find the @papafaga version less fluent.
You also have the possibility to do the opposite of your second version, to put the particular case before the loop, I do it sometimes when the case is trivial.
template <typename Container, typename Separator>
void pretty_print4(const Container& c, const Separator& s)
if (c.empty()) return;
auto it = std::begin(c);
std::cout << *it;
std::advance(it,1);
while (it != std::end(c))
std::cout << s;
std::cout << *it;
std::advance(it,1);
If you talk about performance, I think all versions are worth. Without optimizations, some versions generate more instructions than others, but once in -O3, except one or two instructions, it's almost the same. After, if it really matters, you have to look at the machine code and benchmark.
answered 7 hours ago
Calak
1,0029
add a comment |Â
up vote
1
down vote
We are getting closer to the off-topic "opinion-based" border
What's readable is a matter of taste. Honestly, i find the @papafaga version less fluent.
You also have the possibility to do the opposite of your second version, to put the particular case before the loop, I do it sometimes when the case is trivial.
template <typename Container, typename Separator>
void pretty_print4(const Container& c, const Separator& s)
if (c.empty()) return;
auto it = std::begin(c);
std::cout << *it;
std::advance(it,1);
while (it != std::end(c))
std::cout << s;
std::cout << *it;
std::advance(it,1);
If you talk about performance, I think all versions are worth. Without optimizations, some versions generate more instructions than others, but once in -O3, except one or two instructions, it's almost the same. After, if it really matters, you have to look at the machine code and benchmark.
answered 7 hours ago
Calak
1,0029
add a comment |Â
up vote
1
down vote
up vote
1
down vote
We are getting closer to the off-topic "opinion-based" border
What's readable is a matter of taste. Honestly, i find the @papafaga version less fluent.
You also have the possibility to do the opposite of your second version, to put the particular case before the loop, I do it sometimes when the case is trivial.
template <typename Container, typename Separator>
void pretty_print4(const Container& c, const Separator& s)
if (c.empty()) return;
auto it = std::begin(c);
std::cout << *it;
std::advance(it,1);
while (it != std::end(c))
std::cout << s;
std::cout << *it;
std::advance(it,1);
If you talk about performance, I think all versions are worth. Without optimizations, some versions generate more instructions than others, but once in -O3, except one or two instructions, it's almost the same. After, if it really matters, you have to look at the machine code and benchmark.
answered 7 hours ago
Calak
1,0029
We are getting closer to the off-topic "opinion-based" border
What's readable is a matter of taste. Honestly, i find the @papafaga version less fluent.
You also have the possibility to do the opposite of your second version, to put the particular case before the loop, I do it sometimes when the case is trivial.
template <typename Container, typename Separator>
void pretty_print4(const Container& c, const Separator& s)
if (c.empty()) return;
auto it = std::begin(c);
std::cout << *it;
std::advance(it,1);
while (it != std::end(c))
std::cout << s;
std::cout << *it;
std::advance(it,1);
If you talk about performance, I think all versions are worth. Without optimizations, some versions generate more instructions than others, but once in -O3, except one or two instructions, it's almost the same. After, if it really matters, you have to look at the machine code and benchmark.
answered 7 hours ago
Calak
1,0029
answered 7 hours ago
Calak
1,0029
answered 7 hours ago
Calak
1,0029
answered 7 hours ago
Calak
1,0029
1,0029
add a comment |Â
add a comment |Â
up vote
-1
down vote
I tried this:
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
template <typename Iterator, typename Char>
std::ostream& write_delim(std::ostream& out, Iterator iter, Iterator end, Char delim)
if (iter != end)
out << *iter++;
for (; iter != end; ++iter)
out << delim << *iter;
return out;
int main(int argc, char** argv)
int result = 0;
typedef std::vector<std::string> string_collection;
string_collection strings;
strings.push_back("alpha");
strings.push_back("beta");
strings.push_back("kappa");
strings.push_back("omega");
write_delim(std::cout, strings.begin(), strings.end(), ',') << std::endl;
write_delim(std::cout, strings.begin(), strings.end(), ", ") << std::endl;
return result;
Output results:
alpha,beta,kappa,omega
alpha, beta, kappa, omega
For me, this:
- Clearly communicates the point of the function, both in its name, and in how the code is written.
- Is generic enough to be used in many situations... notice how I can use either a single character or multiple characters between the strings.
- Works on older compilers.
- Works whether you're writing to a file, console, string, or some customized output stream.
Refinements to this might better communicate errors if you chose the wrong type of delimiter for your output.
answered 7 hours ago
Joseph Van Riper
111
New contributor
Joseph Van Riper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Welcome to Code Review! Please refrain from answering low-quality questions that are likely to get closed. Once, you've answered, that limits what can be done to improve the question, making it more likely that your efforts are wasted. It's better to wait until the question is properly ready before you answer!
– Toby Speight
6 hours ago
add a comment |Â
up vote
-1
down vote
I tried this:
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
template <typename Iterator, typename Char>
std::ostream& write_delim(std::ostream& out, Iterator iter, Iterator end, Char delim)
if (iter != end)
out << *iter++;
for (; iter != end; ++iter)
out << delim << *iter;
return out;
int main(int argc, char** argv)
int result = 0;
typedef std::vector<std::string> string_collection;
string_collection strings;
strings.push_back("alpha");
strings.push_back("beta");
strings.push_back("kappa");
strings.push_back("omega");
write_delim(std::cout, strings.begin(), strings.end(), ',') << std::endl;
write_delim(std::cout, strings.begin(), strings.end(), ", ") << std::endl;
return result;
Output results:
alpha,beta,kappa,omega
alpha, beta, kappa, omega
For me, this:
- Clearly communicates the point of the function, both in its name, and in how the code is written.
- Is generic enough to be used in many situations... notice how I can use either a single character or multiple characters between the strings.
- Works on older compilers.
- Works whether you're writing to a file, console, string, or some customized output stream.
Refinements to this might better communicate errors if you chose the wrong type of delimiter for your output.
answered 7 hours ago
Joseph Van Riper
111
New contributor
Joseph Van Riper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Welcome to Code Review! Please refrain from answering low-quality questions that are likely to get closed. Once, you've answered, that limits what can be done to improve the question, making it more likely that your efforts are wasted. It's better to wait until the question is properly ready before you answer!
– Toby Speight
6 hours ago
add a comment |Â
up vote
-1
down vote
up vote
-1
down vote
I tried this:
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
template <typename Iterator, typename Char>
std::ostream& write_delim(std::ostream& out, Iterator iter, Iterator end, Char delim)
if (iter != end)
out << *iter++;
for (; iter != end; ++iter)
out << delim << *iter;
return out;
int main(int argc, char** argv)
int result = 0;
typedef std::vector<std::string> string_collection;
string_collection strings;
strings.push_back("alpha");
strings.push_back("beta");
strings.push_back("kappa");
strings.push_back("omega");
write_delim(std::cout, strings.begin(), strings.end(), ',') << std::endl;
write_delim(std::cout, strings.begin(), strings.end(), ", ") << std::endl;
return result;
Output results:
alpha,beta,kappa,omega
alpha, beta, kappa, omega
For me, this:
- Clearly communicates the point of the function, both in its name, and in how the code is written.
- Is generic enough to be used in many situations... notice how I can use either a single character or multiple characters between the strings.
- Works on older compilers.
- Works whether you're writing to a file, console, string, or some customized output stream.
Refinements to this might better communicate errors if you chose the wrong type of delimiter for your output.
answered 7 hours ago
Joseph Van Riper
111
New contributor
Joseph Van Riper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I tried this:
#include <iostream>
#include <iterator>
#include <string>
#include <vector>
template <typename Iterator, typename Char>
std::ostream& write_delim(std::ostream& out, Iterator iter, Iterator end, Char delim)
if (iter != end)
out << *iter++;
for (; iter != end; ++iter)
out << delim << *iter;
return out;
int main(int argc, char** argv)
int result = 0;
typedef std::vector<std::string> string_collection;
string_collection strings;
strings.push_back("alpha");
strings.push_back("beta");
strings.push_back("kappa");
strings.push_back("omega");
write_delim(std::cout, strings.begin(), strings.end(), ',') << std::endl;
write_delim(std::cout, strings.begin(), strings.end(), ", ") << std::endl;
return result;
Output results:
alpha,beta,kappa,omega
alpha, beta, kappa, omega
For me, this:
- Clearly communicates the point of the function, both in its name, and in how the code is written.
- Is generic enough to be used in many situations... notice how I can use either a single character or multiple characters between the strings.
- Works on older compilers.
- Works whether you're writing to a file, console, string, or some customized output stream.
Refinements to this might better communicate errors if you chose the wrong type of delimiter for your output.
answered 7 hours ago
Joseph Van Riper
111
New contributor
Joseph Van Riper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 7 hours ago
Joseph Van Riper
111
New contributor
Joseph Van Riper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 7 hours ago
Joseph Van Riper
111
answered 7 hours ago
Joseph Van Riper
111
111
New contributor
Joseph Van Riper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Joseph Van Riper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Joseph Van Riper is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Welcome to Code Review! Please refrain from answering low-quality questions that are likely to get closed. Once, you've answered, that limits what can be done to improve the question, making it more likely that your efforts are wasted. It's better to wait until the question is properly ready before you answer!
– Toby Speight
6 hours ago
add a comment |Â
Welcome to Code Review! Please refrain from answering low-quality questions that are likely to get closed. Once, you've answered, that limits what can be done to improve the question, making it more likely that your efforts are wasted. It's better to wait until the question is properly ready before you answer!
– Toby Speight
6 hours ago
Welcome to Code Review! Please refrain from answering low-quality questions that are likely to get closed. Once, you've answered, that limits what can be done to improve the question, making it more likely that your efforts are wasted. It's better to wait until the question is properly ready before you answer!
– Toby Speight
6 hours ago
Welcome to Code Review! Please refrain from answering low-quality questions that are likely to get closed. Once, you've answered, that limits what can be done to improve the question, making it more likely that your efforts are wasted. It's better to wait until the question is properly ready before you answer!
– Toby Speight
6 hours ago
add a comment |Â
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcodereview.stackexchange.com%2fquestions%2f207035%2fprinting-a-comma-separated-list-in-c%23new-answer', 'question_page');
);
Post as a guest
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
2
You're implementing an
ostream_joiner- is this reinventing-the-wheel, or do you need something for straight C++17 withoutstd::experimental?– Toby Speight
6 hours ago
1
So this is not the actual code you have written or are maintaining? Clearly off-topic, I'm afraid.
– Toby Speight
6 hours ago
2
@Kerndog73, if you're talking about me, I'm not intending to be hostile, and apologies if you perceive things that way. I think you may well be able to salvage an on-topic question from this, and there's some very worthwhile observations I'd be able to make if I could see an actual context. It really helps to have compilable code - it's worth writing a small
main()to exercise a function you've made for your project, for example, and you should definitely include the headers and/or definitions you use. I want this to be a good, on-topic question, and it's frustrating that it's not (yet).– Toby Speight
5 hours ago
1
@TobySpeight It's OK. I'm sorry for saying that. The problem is that I was looking for advice about a pattern that is repeated multiple times in different contexts. That's why I wrote code to print a vector. This question is off-topic.
– Kerndog73
5 hours ago
2
@Kerndog73 I’m honestly confused by the rules as well. This question might be better suited for softwareengineering.stackexchange.com (what a mouthful, that URL). But I’m not absolutely sure it is, and I believe there should be a room for such a question somewhere.
– Konrad Rudolph
4 hours ago