Why can std:set (with a single colon) compile?

up vote
55
down vote

favorite

I accidentally wrote

std::set<string> keys;

as:

std:set<string> keys;

but weirdly enough, Visual Studio 2013 still compiles.

Why does this happen?

Actually keys is not only defined, but later used as a set of strings, such as

if(keys.find(keystr)==keys.end())
 keys.insert(keystr);
 toret.push_back(tempv);

edited Aug 28 at 9:13

numbermaniac

62011225

asked Aug 28 at 3:01

athos

2,04012858

10

std: is interpreted as a label for a goto. see: en.cppreference.com/w/cpp/language/goto
â€“Â Sandburg
Aug 28 at 7:05

8

To those voting to close this thing, OP has identified the typo and wants to understand why it does what it does.
â€“Â Joshua
Aug 28 at 16:06

5

Stop close-voting this, people. It's on-topic. We will just reopen it immediately.
â€“Â smci
Aug 29 at 0:40

1

@smci While I agree that this question should stay open, it's not really your place to tell people how to use their votes. Let them use theirs, and you use yours.
â€“Â Jonathon Reinhart
Aug 29 at 0:50

2

@JonathonReinhart: there's no dispute that it isn't on-topic, is there? Noone has suggested any reason why.
â€“Â smci
Aug 29 at 1:41

add a commentÂ |Â

up vote
55
down vote

favorite

I accidentally wrote

std::set<string> keys;

as:

std:set<string> keys;

but weirdly enough, Visual Studio 2013 still compiles.

Why does this happen?

Actually keys is not only defined, but later used as a set of strings, such as

if(keys.find(keystr)==keys.end())
 keys.insert(keystr);
 toret.push_back(tempv);

edited Aug 28 at 9:13

numbermaniac

62011225

asked Aug 28 at 3:01

athos

2,04012858

10

std: is interpreted as a label for a goto. see: en.cppreference.com/w/cpp/language/goto
â€“Â Sandburg
Aug 28 at 7:05

8

To those voting to close this thing, OP has identified the typo and wants to understand why it does what it does.
â€“Â Joshua
Aug 28 at 16:06

5

Stop close-voting this, people. It's on-topic. We will just reopen it immediately.
â€“Â smci
Aug 29 at 0:40

1

@smci While I agree that this question should stay open, it's not really your place to tell people how to use their votes. Let them use theirs, and you use yours.
â€“Â Jonathon Reinhart
Aug 29 at 0:50

2

@JonathonReinhart: there's no dispute that it isn't on-topic, is there? Noone has suggested any reason why.
â€“Â smci
Aug 29 at 1:41

add a commentÂ |Â

up vote
55
down vote

favorite

I accidentally wrote

std::set<string> keys;

as:

std:set<string> keys;

but weirdly enough, Visual Studio 2013 still compiles.

Why does this happen?

Actually keys is not only defined, but later used as a set of strings, such as

if(keys.find(keystr)==keys.end())
 keys.insert(keystr);
 toret.push_back(tempv);

edited Aug 28 at 9:13

numbermaniac

62011225

asked Aug 28 at 3:01

athos

2,04012858

I accidentally wrote

std::set<string> keys;

as:

std:set<string> keys;

but weirdly enough, Visual Studio 2013 still compiles.

Why does this happen?

Actually keys is not only defined, but later used as a set of strings, such as

if(keys.find(keystr)==keys.end())
 keys.insert(keystr);
 toret.push_back(tempv);

edited Aug 28 at 9:13

numbermaniac

62011225

asked Aug 28 at 3:01

athos

2,04012858

edited Aug 28 at 9:13

numbermaniac

62011225

edited Aug 28 at 9:13

numbermaniac

62011225

edited Aug 28 at 9:13

numbermaniac

62011225

asked Aug 28 at 3:01

athos

2,04012858

asked Aug 28 at 3:01

athos

2,04012858

asked Aug 28 at 3:01

athos

2,04012858

10

std: is interpreted as a label for a goto. see: en.cppreference.com/w/cpp/language/goto
â€“Â Sandburg
Aug 28 at 7:05

8

To those voting to close this thing, OP has identified the typo and wants to understand why it does what it does.
â€“Â Joshua
Aug 28 at 16:06

5

Stop close-voting this, people. It's on-topic. We will just reopen it immediately.
â€“Â smci
Aug 29 at 0:40

1

@smci While I agree that this question should stay open, it's not really your place to tell people how to use their votes. Let them use theirs, and you use yours.
â€“Â Jonathon Reinhart
Aug 29 at 0:50

2

@JonathonReinhart: there's no dispute that it isn't on-topic, is there? Noone has suggested any reason why.
â€“Â smci
Aug 29 at 1:41

add a commentÂ |Â

10

std: is interpreted as a label for a goto. see: en.cppreference.com/w/cpp/language/goto
â€“Â Sandburg
Aug 28 at 7:05

8

To those voting to close this thing, OP has identified the typo and wants to understand why it does what it does.
â€“Â Joshua
Aug 28 at 16:06

5

Stop close-voting this, people. It's on-topic. We will just reopen it immediately.
â€“Â smci
Aug 29 at 0:40

1

@smci While I agree that this question should stay open, it's not really your place to tell people how to use their votes. Let them use theirs, and you use yours.
â€“Â Jonathon Reinhart
Aug 29 at 0:50

2

@JonathonReinhart: there's no dispute that it isn't on-topic, is there? Noone has suggested any reason why.
â€“Â smci
Aug 29 at 1:41

std: is interpreted as a label for a goto. see: en.cppreference.com/w/cpp/language/goto
â€“Â Sandburg
Aug 28 at 7:05

To those voting to close this thing, OP has identified the typo and wants to understand why it does what it does.
â€“Â Joshua
Aug 28 at 16:06

Stop close-voting this, people. It's on-topic. We will just reopen it immediately.
â€“Â smci
Aug 29 at 0:40

@smci While I agree that this question should stay open, it's not really your place to tell people how to use their votes. Let them use theirs, and you use yours.
â€“Â Jonathon Reinhart
Aug 29 at 0:50

@JonathonReinhart: there's no dispute that it isn't on-topic, is there? Noone has suggested any reason why.
â€“Â smci
Aug 29 at 1:41

add a commentÂ |Â

2 Answers
2

active

oldest

votes

up vote
90
down vote

accepted

At block scope, an identifier followed by a single colon introduces a label. Thus, your statement is equivalent to:

set<string> keys;

except that it bears the label std and can be jumped to by the statement goto std;.

For some reason, the name set is known to the compiler---perhaps you did using namespace std;, or using std::set;, or something like that, or perhaps you defined your own set type somewhere.

answered Aug 28 at 3:03

Brian

60k791173

42

This is another reason to avoid using namespace std; and using std::set;
â€“Â R Sahu
Aug 28 at 3:40

31

There are good arguments to be made against using namespace std/using std::set, but I'm not sure this is one of them... the main argument is usually that namespaces are there to prevent collisions, but if there is a non-std 'set' to collide with, then std: set<...> would probably be valid. Common practice is to limit any such using declarations to another namespace/function, but this problem could just as easily happen in that scope. I would sooner expect a typo to creep in rewriting std::chrono::high_resolution_clock, etc. ad nauseum than this label typo (the first I've seen like it.)
â€“Â John P
Aug 28 at 11:50

add a commentÂ |Â

up vote
10
down vote

In the second case, std is a label. It is the same as spelling default incorrectly in a case statement.

answered Aug 28 at 3:04

cup

4,5802924

add a commentÂ |Â

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

up vote
90
down vote

accepted

At block scope, an identifier followed by a single colon introduces a label. Thus, your statement is equivalent to:

set<string> keys;

except that it bears the label std and can be jumped to by the statement goto std;.

For some reason, the name set is known to the compiler---perhaps you did using namespace std;, or using std::set;, or something like that, or perhaps you defined your own set type somewhere.

answered Aug 28 at 3:03

Brian

60k791173

42

This is another reason to avoid using namespace std; and using std::set;
â€“Â R Sahu
Aug 28 at 3:40

31

There are good arguments to be made against using namespace std/using std::set, but I'm not sure this is one of them... the main argument is usually that namespaces are there to prevent collisions, but if there is a non-std 'set' to collide with, then std: set<...> would probably be valid. Common practice is to limit any such using declarations to another namespace/function, but this problem could just as easily happen in that scope. I would sooner expect a typo to creep in rewriting std::chrono::high_resolution_clock, etc. ad nauseum than this label typo (the first I've seen like it.)
â€“Â John P
Aug 28 at 11:50

add a commentÂ |Â

up vote
90
down vote

accepted

At block scope, an identifier followed by a single colon introduces a label. Thus, your statement is equivalent to:

set<string> keys;

except that it bears the label std and can be jumped to by the statement goto std;.

For some reason, the name set is known to the compiler---perhaps you did using namespace std;, or using std::set;, or something like that, or perhaps you defined your own set type somewhere.

answered Aug 28 at 3:03

Brian

60k791173

42

This is another reason to avoid using namespace std; and using std::set;
â€“Â R Sahu
Aug 28 at 3:40

31

There are good arguments to be made against using namespace std/using std::set, but I'm not sure this is one of them... the main argument is usually that namespaces are there to prevent collisions, but if there is a non-std 'set' to collide with, then std: set<...> would probably be valid. Common practice is to limit any such using declarations to another namespace/function, but this problem could just as easily happen in that scope. I would sooner expect a typo to creep in rewriting std::chrono::high_resolution_clock, etc. ad nauseum than this label typo (the first I've seen like it.)
â€“Â John P
Aug 28 at 11:50

add a commentÂ |Â

up vote
90
down vote

accepted

At block scope, an identifier followed by a single colon introduces a label. Thus, your statement is equivalent to:

set<string> keys;

except that it bears the label std and can be jumped to by the statement goto std;.

For some reason, the name set is known to the compiler---perhaps you did using namespace std;, or using std::set;, or something like that, or perhaps you defined your own set type somewhere.

answered Aug 28 at 3:03

Brian

60k791173

At block scope, an identifier followed by a single colon introduces a label. Thus, your statement is equivalent to:

set<string> keys;

except that it bears the label std and can be jumped to by the statement goto std;.

For some reason, the name set is known to the compiler---perhaps you did using namespace std;, or using std::set;, or something like that, or perhaps you defined your own set type somewhere.

answered Aug 28 at 3:03

Brian

60k791173

answered Aug 28 at 3:03

Brian

60k791173

answered Aug 28 at 3:03

Brian

60k791173

answered Aug 28 at 3:03

Brian

60k791173

42

This is another reason to avoid using namespace std; and using std::set;
â€“Â R Sahu
Aug 28 at 3:40

31

There are good arguments to be made against using namespace std/using std::set, but I'm not sure this is one of them... the main argument is usually that namespaces are there to prevent collisions, but if there is a non-std 'set' to collide with, then std: set<...> would probably be valid. Common practice is to limit any such using declarations to another namespace/function, but this problem could just as easily happen in that scope. I would sooner expect a typo to creep in rewriting std::chrono::high_resolution_clock, etc. ad nauseum than this label typo (the first I've seen like it.)
â€“Â John P
Aug 28 at 11:50

add a commentÂ |Â

42

This is another reason to avoid using namespace std; and using std::set;
â€“Â R Sahu
Aug 28 at 3:40

31

There are good arguments to be made against using namespace std/using std::set, but I'm not sure this is one of them... the main argument is usually that namespaces are there to prevent collisions, but if there is a non-std 'set' to collide with, then std: set<...> would probably be valid. Common practice is to limit any such using declarations to another namespace/function, but this problem could just as easily happen in that scope. I would sooner expect a typo to creep in rewriting std::chrono::high_resolution_clock, etc. ad nauseum than this label typo (the first I've seen like it.)
â€“Â John P
Aug 28 at 11:50

This is another reason to avoid using namespace std; and using std::set;
â€“Â R Sahu
Aug 28 at 3:40

There are good arguments to be made against using namespace std/using std::set, but I'm not sure this is one of them... the main argument is usually that namespaces are there to prevent collisions, but if there is a non-std 'set' to collide with, then std: set<...> would probably be valid. Common practice is to limit any such using declarations to another namespace/function, but this problem could just as easily happen in that scope. I would sooner expect a typo to creep in rewriting std::chrono::high_resolution_clock, etc. ad nauseum than this label typo (the first I've seen like it.)
â€“Â John P
Aug 28 at 11:50

add a commentÂ |Â

up vote
10
down vote

In the second case, std is a label. It is the same as spelling default incorrectly in a case statement.

answered Aug 28 at 3:04

cup

4,5802924

add a commentÂ |Â

up vote
10
down vote

In the second case, std is a label. It is the same as spelling default incorrectly in a case statement.

answered Aug 28 at 3:04

cup

4,5802924

add a commentÂ |Â

up vote
10
down vote

In the second case, std is a label. It is the same as spelling default incorrectly in a case statement.

answered Aug 28 at 3:04

cup

4,5802924

In the second case, std is a label. It is the same as spelling default incorrectly in a case statement.

answered Aug 28 at 3:04

cup

4,5802924

answered Aug 28 at 3:04

cup

4,5802924

answered Aug 28 at 3:04

cup

4,5802924

answered Aug 28 at 3:04

cup

4,5802924

add a commentÂ |Â

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