Am Dienstag, 14. Mai 2013, 19:05:13 schrieb Vojtěch Novák:
> hello,
> I'm working on a C++ package for ROS (robot operating system) that uses a C
> library libccv.a. ROS uses CMake which is why I am asking here. Asking at
> ROS answers did not help and I am totally stuck.
[...]
From a quick look at your pastes and your cmake lists, i can't see anything
that should cause the problem you're facing here.
However, from the error message that gcc gives, it can be assumed that there
is a problem in the library you're trying to use:
When using C code from a C++ library, the C code must be wrapped with a
extern "C"
declaration.
This program:
struct bar;
void foo(bar*);
int main() {
bar* b;
foo(b);
}
will give the error:
x.cpp:(.text+0x10): undefined reference to `foo(bar*)'
when compiled as c++.
Contrary this program:
extern "C" {
struct bar;
void foo(struct bar*);
}
int main() {
bar* b;
foo(b);
}
will result in the error:
x.cpp:(.text+0x10): undefined reference to `foo'
Note that the former refers to a mangled c++ symbol while the latter refers to
an unmangled C symbol.
Usually, a C header file should include the following lines:
#ifdef __cplusplus
extern "c" {
#endif
// normal C-Code here
#ifdef __cplusplus
}
#endif
As a workaround, you could write a file named ccv.hpp and put this content
into it:
extern "C" {
#include "ccv.h"
}
Then go through your C++ sources and change every include of "ccv.h" to
"ccv.hpp".
Hope this helps,
Sascha
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