Why does overloading operator<< to print Eigen class member result in a segfault?

up vote
7
down vote

favorite

For the following struct

struct TestClass 
 TestClass() : mat(Eigen::Matrix3i::Zero()) 
 Eigen::Matrix3i mat;
;

I would like to have an overloaded operator<< to print the mat member to std::cout. I tried

std::ostream& operator<<(std::ostream& out, const TestClass& object) 
 out << object.mat;

This results in a segfault. Can anyone explain to me why?

A minimum working example:

#include <iostream>
#include <Eigen/Core>

struct TestClass 
 TestClass() : mat(Eigen::Matrix3i::Zero()) 
 Eigen::Matrix3i mat;
;

std::ostream& operator<<(std::ostream& out, const TestClass& object) 
 out << object.mat;


int main() 
 TestClass testObject;

 std::cout << testObject.mat << "nn"; // This works fine.
 std::cout << testObject << 'n'; // This results in a segfault.

 return 0;

I'm compiling with g++ version 7.3.0 and Eigen version 3.4 on Ubuntu 18.04.

asked 1 hour ago

red

414

New contributor

5

You must return the std::ostream reference from the operator overload implementation, e.g. return out << object.mat;. Non-void functions not returning anything are usually tagged with some compiler warnings, it might be worth enabling these (e.g. -Wall -pedantic).
â€“Â lubgr
58 mins ago

add a commentÂ |Â

up vote
7
down vote

favorite

For the following struct

struct TestClass 
 TestClass() : mat(Eigen::Matrix3i::Zero()) 
 Eigen::Matrix3i mat;
;

I would like to have an overloaded operator<< to print the mat member to std::cout. I tried

std::ostream& operator<<(std::ostream& out, const TestClass& object) 
 out << object.mat;

This results in a segfault. Can anyone explain to me why?

A minimum working example:

#include <iostream>
#include <Eigen/Core>

struct TestClass 
 TestClass() : mat(Eigen::Matrix3i::Zero()) 
 Eigen::Matrix3i mat;
;

std::ostream& operator<<(std::ostream& out, const TestClass& object) 
 out << object.mat;


int main() 
 TestClass testObject;

 std::cout << testObject.mat << "nn"; // This works fine.
 std::cout << testObject << 'n'; // This results in a segfault.

 return 0;

I'm compiling with g++ version 7.3.0 and Eigen version 3.4 on Ubuntu 18.04.

asked 1 hour ago

red

414

New contributor

5

You must return the std::ostream reference from the operator overload implementation, e.g. return out << object.mat;. Non-void functions not returning anything are usually tagged with some compiler warnings, it might be worth enabling these (e.g. -Wall -pedantic).
â€“Â lubgr
58 mins ago

add a commentÂ |Â

up vote
7
down vote

favorite

For the following struct

struct TestClass 
 TestClass() : mat(Eigen::Matrix3i::Zero()) 
 Eigen::Matrix3i mat;
;

I would like to have an overloaded operator<< to print the mat member to std::cout. I tried

std::ostream& operator<<(std::ostream& out, const TestClass& object) 
 out << object.mat;

This results in a segfault. Can anyone explain to me why?

A minimum working example:

#include <iostream>
#include <Eigen/Core>

struct TestClass 
 TestClass() : mat(Eigen::Matrix3i::Zero()) 
 Eigen::Matrix3i mat;
;

std::ostream& operator<<(std::ostream& out, const TestClass& object) 
 out << object.mat;


int main() 
 TestClass testObject;

 std::cout << testObject.mat << "nn"; // This works fine.
 std::cout << testObject << 'n'; // This results in a segfault.

 return 0;

I'm compiling with g++ version 7.3.0 and Eigen version 3.4 on Ubuntu 18.04.

asked 1 hour ago

red

414

New contributor

For the following struct

struct TestClass 
 TestClass() : mat(Eigen::Matrix3i::Zero()) 
 Eigen::Matrix3i mat;
;

I would like to have an overloaded operator<< to print the mat member to std::cout. I tried

std::ostream& operator<<(std::ostream& out, const TestClass& object) 
 out << object.mat;

This results in a segfault. Can anyone explain to me why?

A minimum working example:

#include <iostream>
#include <Eigen/Core>

struct TestClass 
 TestClass() : mat(Eigen::Matrix3i::Zero()) 
 Eigen::Matrix3i mat;
;

std::ostream& operator<<(std::ostream& out, const TestClass& object) 
 out << object.mat;


int main() 
 TestClass testObject;

 std::cout << testObject.mat << "nn"; // This works fine.
 std::cout << testObject << 'n'; // This results in a segfault.

 return 0;

I'm compiling with g++ version 7.3.0 and Eigen version 3.4 on Ubuntu 18.04.

c++ eigen member cout

asked 1 hour ago

red

414

New contributor

asked 1 hour ago

red

414

New contributor

asked 1 hour ago

red

414

New contributor

asked 1 hour ago

red

414

asked 1 hour ago

red

414

New contributor

red is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

5

You must return the std::ostream reference from the operator overload implementation, e.g. return out << object.mat;. Non-void functions not returning anything are usually tagged with some compiler warnings, it might be worth enabling these (e.g. -Wall -pedantic).
â€“Â lubgr
58 mins ago

add a commentÂ |Â

5

You must return the std::ostream reference from the operator overload implementation, e.g. return out << object.mat;. Non-void functions not returning anything are usually tagged with some compiler warnings, it might be worth enabling these (e.g. -Wall -pedantic).
â€“Â lubgr
58 mins ago

You must return the std::ostream reference from the operator overload implementation, e.g. return out << object.mat;. Non-void functions not returning anything are usually tagged with some compiler warnings, it might be worth enabling these (e.g. -Wall -pedantic).
â€“Â lubgr
58 mins ago

add a commentÂ |Â

1 Answer
1

active

oldest

votes

up vote
9
down vote

accepted

The return value of the overloaded operator<< is std::ostream&. However, you are not returning anything from it.

Do the following:

out << object.mat;
return out;

or alternatively,

return out << object.mat;

edited 42 mins ago

john

33.6k12645

answered 55 mins ago

P.W

3,145221

Or just return out << object.mat;
â€“Â john
48 mins ago

@john: Added your suggestion too. Thanks.
â€“Â P.W
45 mins ago

add a commentÂ |Â

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1 Answer
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active

oldest

votes

1 Answer
1

active

oldest

votes

up vote
9
down vote

accepted

The return value of the overloaded operator<< is std::ostream&. However, you are not returning anything from it.

Do the following:

out << object.mat;
return out;

or alternatively,

return out << object.mat;

edited 42 mins ago

john

33.6k12645

answered 55 mins ago

P.W

3,145221

Or just return out << object.mat;
â€“Â john
48 mins ago

@john: Added your suggestion too. Thanks.
â€“Â P.W
45 mins ago

add a commentÂ |Â

up vote
9
down vote

accepted

The return value of the overloaded operator<< is std::ostream&. However, you are not returning anything from it.

Do the following:

out << object.mat;
return out;

or alternatively,

return out << object.mat;

edited 42 mins ago

john

33.6k12645

answered 55 mins ago

P.W

3,145221

Or just return out << object.mat;
â€“Â john
48 mins ago

@john: Added your suggestion too. Thanks.
â€“Â P.W
45 mins ago

add a commentÂ |Â

up vote
9
down vote

accepted

The return value of the overloaded operator<< is std::ostream&. However, you are not returning anything from it.

Do the following:

out << object.mat;
return out;

or alternatively,

return out << object.mat;

edited 42 mins ago

john

33.6k12645

answered 55 mins ago

P.W

3,145221

The return value of the overloaded operator<< is std::ostream&. However, you are not returning anything from it.

Do the following:

out << object.mat;
return out;

or alternatively,

return out << object.mat;

edited 42 mins ago

john

33.6k12645

answered 55 mins ago

P.W

3,145221

edited 42 mins ago

john

33.6k12645

edited 42 mins ago

john

33.6k12645

edited 42 mins ago

john

33.6k12645

answered 55 mins ago

P.W

3,145221

answered 55 mins ago

P.W

3,145221

answered 55 mins ago

P.W

3,145221

Or just return out << object.mat;
â€“Â john
48 mins ago

@john: Added your suggestion too. Thanks.
â€“Â P.W
45 mins ago

add a commentÂ |Â

Or just return out << object.mat;
â€“Â john
48 mins ago

@john: Added your suggestion too. Thanks.
â€“Â P.W
45 mins ago

Or just return out << object.mat;
â€“Â john
48 mins ago

@john: Added your suggestion too. Thanks.
â€“Â P.W
45 mins ago

add a commentÂ |Â

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