Can I use a C++ function pointer instead of a C one

[Franz]

Hello

I have some C code where I can register function pointers for
callback:

[c]
/* reaction.h */
...
typedef void (*FP) (int,int);
addReaction(FP);
...

Can I pass a "c++" function (not a member function) from c++ code to
'addRection()' ?

[c++]
/* x.hpp */
...
void xFunc(int a, int b);
...

/* x.cpp */
#include "x.hpp"
#include "reaction.h"
...
ini()
{
addReaction(&xFunc);
}

Or do I have to declare that function as extern "C":
[c++]
/* x.hpp */
...
extern "C" void xFunc(int a, int b);
...

Thanks
Franz

 

[Thomas Matthews]

Hello

I have some C code where I can register function pointers for
callback:

[c]
/* reaction.h */
...
typedef void (*FP) (int,int);
addReaction(FP);
...

Can I pass a "c++" function (not a member function) from c++ code to
'addRection()' ?

[snip]

Yes, you can pass a pointer to a non-member C++ function to a
C function. However, if the C function was compiled in a
separate translation unit with a C compiler you may have to
declare the function as 'extern "C";'.

Or do I have to declare that function as extern "C":

This would be the safest technique.

Thanks
Franz

--
Thomas Matthews

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[Ron Natalie]

Yes, you can pass a pointer to a non-member C++ function to a
C function. However, if the C function was compiled in a
separate translation unit with a C compiler you may have to
declare the function as 'extern "C";'.

You've lost me on that one. Just how do you get a C function compiled
into the same translation unit as a C++ function pointer?

 

[Thomas Matthews]

You've lost me on that one. Just how do you get a C function compiled
into the same translation unit as a C++ function pointer?

Sorry, let me clarify my thoughts.
My understanding in this scenario is that there is a module,
lets say, old_func.c, which contains a non-member function:
void My_Function(void)
{
/* yada, yada, yada */
}
Let a C compiler (or a C++ compiler compiling in C mode)
translate this into old_func.o.

The function has the C language naming convention because
it was compiled using a C compiler.

If it was compiled using a C++ compiler, it _may_ have
a different {mangled} name than the C version.

Sooo, my point was that a function pointer in C++
may have an issue between when pointing to a function
compiled in C languge mode versus when it was
compiled in C++ mode. At the execution level, there
should be no difference. I believe only the Linker
{should there be one} would be the part that "chokes"
because of the naming conventions.

--
Thomas Matthews

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http://www.slack.net/~shiva/welcome.txt
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alt.comp.lang.learn.c-c++ faq:
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Other sites:
http://www.josuttis.com -- C++ STL Library book

 

[Bob Hairgrove]

My understanding in this scenario is that there is a module,
lets say, old_func.c, which contains a non-member function:
void My_Function(void)
{
/* yada, yada, yada */
}
Let a C compiler (or a C++ compiler compiling in C mode)
translate this into old_func.o.

The function has the C language naming convention because
it was compiled using a C compiler.

If it was compiled using a C++ compiler, it _may_ have
a different {mangled} name than the C version.

Sooo, my point was that a function pointer in C++
may have an issue between when pointing to a function
compiled in C languge mode versus when it was
compiled in C++ mode. At the execution level, there
should be no difference. I believe only the Linker
{should there be one} would be the part that "chokes"
because of the naming conventions.

If the C function is not exported from the C++ module, it should link
OK because most compilers will compile and link the function with C
linkage. This usually happens automatically when a file has a ".c" and
not a ".cpp" extension.

If the C function is being imported from an older library, it must be
imported with C linkage (extern "C"...). It should have a
corresponding prototype in your C++ code. You may need to inclose the
#include pre-processor directive in something like this:

#ifdef __cplusplus
{ extern "C"
#endif
#include "OldHeader.h"
#ifdef __cplusplus
}
#endif