gcc: Linking an External Library

Question

In program.c, I would like to use a method 'avcodec_register_all()' defined in libavcodec/avcodec.h.

Running

gcc program.c -L$HOME/ffmpeg/lib/libavfilter.a -L$HOME/ffmpeg/lib/libavcodec.a

Gives me an error

/tmp/ccNeQywU.o: In function `main': program.c:(.text+0x3f): undefined reference to `avcodec_register_all' collect2: ld returned 1 exit status

Spelling is correct and the function is defined. Why is this happening?

program.c

#include <stdio.h> int main (int args, char *argv[]) { avcodec_register_all(); }

is avcodec_register_all one of them? or is that error gone now? — stardust
– stardust, Commented Mar 14, 2014 at 21:27
avcodec_register_all undefined reference error is gone, but I have undefined reference errors for other methods. — jamie_y
– jamie_y, Commented Mar 14, 2014 at 21:35
Then look for the libraries where those functions are defined in and add them the same way. — stardust
– stardust, Commented Mar 14, 2014 at 21:36

Claudiordgz · Accepted Answer · 2014-03-14 21:53:11Z

4

It is like this

gcc -static -lavfilter -lavcodec -L/HOME/ffmpeg/lib/

You need to include the file avcodec.h and also add the path to that file in your include path flags to gcc.

gcc -static -lavfilter -lavcodec -L$HOME/ffmpeg/lib/ -I$HOME/ffmpeg/include

The static is given because your are trying to use a *.a library and not *.so (dynamic).

edited Mar 14, 2014 at 21:53

answered Mar 14, 2014 at 21:24

Claudiordgz

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4 Comments

jamie_y Over a year ago

Running 'gcc -lavfilter -lavcondec -L/$HOME/ffmpeg/lib/ -I/$HOME/ffmpeg/include program.c' gives me '/usr/bin/ld: cannot find -lavcondec collect2: ld returned 1 exit status'

Claudiordgz Over a year ago

I had a typo as well, I used avcondec when is avcodec, sorry

jamie_y Over a year ago

Running 'gcc -static -lavfilter -lavcodec -L/$HOME/ffmpeg/lib/ -I/$HOME/ffmpeg/include program.c' gives 'undefined reference to `avcodec_register_all''

Claudiordgz Over a year ago

check edit again, please add the include "avcodec.h"

abhi · Accepted Answer · 2014-03-14 21:25:02Z

0

Use -lavcodec with the existing parameters to gcc

answered Mar 14, 2014 at 21:25

abhi

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Comments

Andrej Adamenko · Accepted Answer · 2014-03-14 22:50:20Z

One of the reasons may be that the function avcodec_register_all() is defined in a C++ file. It should be defined as extern "C" in avcodec.h and the library should be compiled with this proper avcodec.h.

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