64bit osx (part II) linking
I am trying to link the libx264 library to one of my apps but I am getting linking errors saying it can not find various symbols for the x86_64 architecture:
Undefined symbols for architecture x86_64: “x264_param_default_preset(x264_param_t*, char const*, char const*)”, referenced from:
I have verified that I compiled the libx264 library using x86_64:
>lipo -info libx264.a
input file libx264.a is not a fat file
Non-fat file: libx264.a is architecture: x86_64
I also checked to see if the missing symbols exist in the library:
> nm libx264.a | grep x264_param_default_preset
0000000000001710 T _x264_param_default_preset
0000000000005e88 S _x264_param_default_preset.eh
I am trying to link as a static library.
Are there some additional parameters I need to set when compiling libraries to get them to be compatible with Qt or can someone point me in the right direction?
Thanks again.
-=ben
5 replies
Could you post the part of your .pro file, where you are linking your libs?
Also, there was a similar thread before (maybe you have the same problem):
http://developer.qt.nokia.com/forums/viewthread/5665
Sure thing:
- TARGET = myLib
- TEMPLATE = lib
- ... headers/source removed for readability ...
- macx {
- LIBS += /Developer/SDKs/MacOSX10.6.sdk/System/Library/Frameworks/AppKit.framework/Versions/Current/AppKit \
- /Developer/SDKs/MacOSX10.6.sdk/System/Library/Frameworks/OpenGL.framework/Versions/Current/OpenGL \
- ../../../common/x264/libx264.a \
- ../../../common/ffmpeg/libswscale/libswscale.a
- QMAKE_LFLAGS_SONAME = -Wl,-install_name,@executable_path/../Frameworks/
- }
Thanks for the other posting link, unfortunately it has not helped me.
Thanks.
-=ben
I can reproduce the problem. It’s nothing Qt specific, though.
The x264 library does not support C++ out of the box. It is a pure C library, so it uses the C style name mangling [en.wikipedia.org], if you just include the headers in a C++ source, the compiler wants to apply C++ style name mangling – so it tries to link different names which are not available in the lib.
So, the solution simple: Wrap the #include with extern “C” this way:
- #include <stdint.h>
- // enforce C style name mangling
- extern "C" {
- #include "x264.h"
- }
This switches on C name mangling for the functions in this header file.
If you do not setup anything, then the default name mangling is used. If you have a C library that is usesful from C++ as well, it is good practice to put that extern stuff into the header of your libraray. The usual pattern is:
- #ifdef __cplusplus
- extern "C" {
- #endif
- // your actual header files goes here
- #ifdef __cplusplus
- }
- #endif
See the C++ FAQ on ‘How to mix C and C++’ [parashift.com] for some more details.
Unfortunately there is no easy way to tell if the header has the “extern” other than actually looking into it.
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