Libav linking error: undefined references
ffmpeg, g++, libav, linker
Solution
The libraries are C. The library headers don't include an extern "C" when compiled as C++. Do this in your C++ source:
extern "C" {
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
}
Or, more generically, for mixed C and C++ source:
#ifdef __cplusplus
extern "C" {
#endif
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#ifdef __cplusplus
}
#endif
And you should be fine.
Problem
Here's my problem: - I built ffmpeg from source (version 1.2), the libav* libraries are in /usr/local/lib and they're static - I'm compiling a ns3 (www.nsnam.org) module, so my only control over the linker is through the env variable LINKFLAGS - In the source the headers are in a "extern C" block, so it's not the usual g++ name mangling - I set LINKFLAGS="-I/usr/local/include/libavformat -I/usr/local/include/libavcodec -I/usr/local/include/libavutil -L/usr/local/lib -lavformat -lavcodec -lavutil", and the linker can't seem to find any of the libav* functions I call (I get a lot of "undefined reference" and then "collect2: error: ld returned status 1" Can anyone help me? Thanks... edit: here are a few of the undefined reference messages: ``` ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `av_guess_format' ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `av_read_frame' ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `avformat_write_header' ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `av_interleaved_write_frame' ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `av_find_stream_info' ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `av_register_all' ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `av_init_packet' ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `avformat_alloc_context' ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `av_dump_format' ./libns3.14.1-qoe-monitor-debug.so: undefined reference to `avio_close' ``` edit2: here is the message I get after "build failed": ``` -> task in 'scratch-simulator' failed (exit status 1): {task 53952272: cxxprogram scratch-simulator.cc.1.o -> scratch-simulator} ['/usr/bin/g++', '-I/usr/local/include/libavcodec', '-I/usr/local/include/libavformat/', '-I/usr/local/include/libavutil/', '-L/usr/local/lib', '-I/usr/local /include/libavcodec', '-I/usr/local/include/libavformat/', '-I/usr/local/include /libavutil/', '-L/usr/local/lib', '-pthread', '-pthread', '-Wl,-z,relro', 'scratch/scratch-simulator.cc.1.o', '-o', '/home/fede/Thesis/ns-allinone-3.14.1 /ns-3.14.1/build/scratch/scratch-simulator', '-Wl,-Bstatic', '-Wl,-Bdynamic', '-Wl,--no-as-needed', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L.', '-L/usr/lib', '-lns3.14.1-test-debug', '-lns3.14.1- csma-layout-debug', '-lns3.14.1-point-to-point-layout-debug', '-lns3.14.1-netanim- debug', '-lns3.14.1-lte-debug', '-lns3.14.1-spectrum-debug', '-lns3.14.1-antenna- debug', '-lns3.14.1-aodv-debug', '-lns3.14.1-dsdv-debug', '-lns3.14.1-dsr-debug', '-lns3.14.1-mesh-debug', '-lns3.14.1-olsr-debug', '-lns3.14.1-csma-debug', '-lns3.14.1- wimax-debug', '-lns3.14.1-applications-debug', '-lns3.14.1-virtual-net-device-debug', '-lns3.14.1-uan-debug', '-lns3.14.1-energy-debug', '-lns3.14.1-flow-monitor-debug', '-lns3.14.1-nix-vector-routing-debug', '-lns3.14.1-tap-bridge-debug', '-lns3.14.1- visualizer-debug', '-lns3.14.1-internet-debug', '-lns3.14.1-bridge-debug', '-lns3.14.1- point-to-point-debug', '-lns3.14.1-mpi-debug', '-lns3.14.1-wifi-debug', '-lns3.14.1- buildings-debug', '-lns3.14.1-propagation-debug', '-lns3.14.1-mobility-debug', '-lns3.14.1-config-store-debug', '-lns3.14.1-tools-debug', '-lns3.14.1-stats-debug', '-lns3.14.1-emu-debug', '-lns3.14.1-topology-read-debug', '-lns3.14.1-network-debug', '-lns3.14.1-qoe-monitor-debug', '-lns3.14.1-core-debug', '-lrt', '-lgsl', '-lgslcblas', '-lm', '-ldl', '-lgtk-x11-2.0', '-lgdk-x11-2.0', '-latk-1.0', '-lgio-2.0', '-lpangoft2-1.0', '-lpangocairo-1.0', '-lgdk_pixbuf-2.0', '-lcairo', '-lpango-1.0', '-lfreetype', '-lfontconfig', '-lgobject-2.0', '-lglib-2.0', '-lxml2', '-lpython2.7'] ```