> On 2016年09月02日, at 22:32, R n <[email protected]> wrote:
> I am writing a C++ library which is based on OpenCV. I want to use it in a
> Ffmpeg filter (written in C), so I write a wrapper of the library using C.
> The wrapper consists of a C header file and some C functions which call the
> C++ functions (in the C++ files). I expect the FFmpeg filter to only include
> the C header and call the C functions.
…
> However, I get the following error when compiling FFmpeg:
> .../binutils/2.25/centos6-native/da39a3e/bin/ld:
> .../mylibrary/0.1/gcc-4.9-glibc-2.20/80414d5/lib/libmylibrary.a(mylibrary_file.cpp.o):
> undefined reference to symbol '_ZdlPv@@GLIBCXX_3.4'
> .../libgcc/4.9.x/gcc-4.9-glibc-2.20/024dbc3/lib/libstdc++.so: error adding
> symbols: DSO missing from command line
Your approach is correct, but C++ “mangles” function names to make them unique
when considering parameters and such. You need to specify C linkage, so in
your .h file, wrap it in extern “C”:
#ifdef __cplusplus
#warning is c++
extern "C" {
#endif
char foo (int);
#ifdef __cplusplus
}
#endif
You need to #include the .h file in the corresponding .cpp file, so the C++
compiler knows not to mangle those particular function names when they’re
compiled.
Perette
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