friends namespaces and operators

[glen stark]

Hi.

I had an interesting experience with a brand x compiler recently. I had
class defined within a namespace, and in that class I declared the "<<"
operator as a friend to that class. Then, in the cpp code I implemented
the operator overloading within a "using namespace" context, only to get
access errers. To get it to work I had to put a namespaceName:: in
front of the operator keyword...

for your edification, here is a sample code:
================
HEADER FILE

#include <string>
#include <ostream>

namespace voxel{
class PrivateClass{
public:
PrivateClass():info("hiya"){};
friend std:stream& operator<<(std:stream&, const PrivateClass&);
private:
std::string info;
};
}
===================
CPP FILE

#include "stdafx.h"
#include "PrivateClass.h"
using namespace voxel;
std:stream& voxel:perator<<(std:stream& os, const PrivateClass& pc)
{
os<<pc.info;
return os;
}

int main(int argc, char* argv[])
{

PrivateClass pc;
std::cout<<pc;
return 0;

}


=====end of code

So my question is: is this a compiler bug, or is this a loophole in the
standard somehow? If it's a compiler bug, does the standard imply that
it should behave as i would think, or what? I would very much like any
clarification you can offer me.

 

[John Harrison]

Hi.

I had an interesting experience with a brand x compiler recently. I had
class defined within a namespace, and in that class I declared the "<<"
operator as a friend to that class. Then, in the cpp code I implemented
the operator overloading within a "using namespace" context, only to get
access errers. To get it to work I had to put a namespaceName:: in
front of the operator keyword...

for your edification, here is a sample code:
================
HEADER FILE

#include <string>
#include <ostream>

namespace voxel{
class PrivateClass{
public:
PrivateClass():info("hiya"){};
friend std:stream& operator<<(std:stream&, const PrivateClass&);
private:
std::string info;
};
}
===================
CPP FILE

#include "stdafx.h"
#include "PrivateClass.h"
using namespace voxel;
std:stream& voxel:perator<<(std:stream& os, const PrivateClass& pc)
{
os<<pc.info;
return os;
}

int main(int argc, char* argv[])
{

PrivateClass pc;
std::cout<<pc;
return 0;

}


=====end of code

So my question is: is this a compiler bug, or is this a loophole in the
standard somehow?

Neither, its your understanding of C++ that is wrong.

If it's a compiler bug, does the standard imply that
it should behave as i would think, or what? I would very much like any
clarification you can offer me.

You seem to be assuming that writing 'using namespace voxel;' should put
subsequent definitions in the voxel namespace but that is not the case (if
it were the case then you would have put main in the voxel namespace). Or
maybe you are thinking that the compiler should somehow make a connection
between the operator<< in your source file and the operator<< in your header
file, but as far as the compiler is concerned they are just similar
functions in different namespaces.

'Using namespace ...' affects how names are looked up, it does not affect
which namespace names are defined in. The only way to do that is this

namespace voxel
{
std:stream& operator<<(std:stream& os, const PrivateClass& pc)
{
...
}
}

or this

std:stream& voxel:perator<<(std:stream& os, const PrivateClass&
pc)
{
...
}

john

 

[glen stark]

Hi.

I had an interesting experience with a brand x compiler recently. I had
class defined within a namespace, and in that class I declared the "<<"
operator as a friend to that class. Then, in the cpp code I implemented
the operator overloading within a "using namespace" context, only to get
access errers. To get it to work I had to put a namespaceName:: in
front of the operator keyword...

for your edification, here is a sample code:
================
HEADER FILE

#include <string>
#include <ostream>

namespace voxel{
class PrivateClass{
public:
PrivateClass():info("hiya"){};
friend std:stream& operator<<(std:stream&, const PrivateClass&);
private:
std::string info;
};
}
===================
CPP FILE

#include "stdafx.h"
#include "PrivateClass.h"
using namespace voxel;
std:stream& voxel:perator<<(std:stream& os, const PrivateClass& pc)
{
os<<pc.info;
return os;
}

int main(int argc, char* argv[])
{

PrivateClass pc;
std::cout<<pc;
return 0;

}


=====end of code

So my question is: is this a compiler bug, or is this a loophole in the
standard somehow?

Neither, its your understanding of C++ that is wrong.

If it's a compiler bug, does the standard imply that
it should behave as i would think, or what? I would very much like any
clarification you can offer me.

You seem to be assuming that writing 'using namespace voxel;' should put
subsequent definitions in the voxel namespace but that is not the case (if
it were the case then you would have put main in the voxel namespace). Or
maybe you are thinking that the compiler should somehow make a connection
between the operator<< in your source file and the operator<< in your header
file, but as far as the compiler is concerned they are just similar
functions in different namespaces.

'Using namespace ...' affects how names are looked up, it does not affect
which namespace names are defined in. The only way to do that is this

namespace voxel
{
std:stream& operator<<(std:stream& os, const PrivateClass& pc)
{
...
}
}

or this

std:stream& voxel:perator<<(std:stream& os, const PrivateClass&
pc)
{
...
}

john

Thanks, that clears it up.

Glen