gcc : undefined reference to 'function'

Question

I have installed a C library on my computer (Ubuntu) called xx, whose header file is at /usr/local/include/xx/xx.h and the .a file and .so file are in the path /usr/local/lib named libxx.a and libxx.so.

The test file:

#include<xx/xx.h>
#include<stdio.h>
int main(){
 printf("Test\n");
 call_function_declared_in_the_header_file();
 return 0;
}

When I use gcc to compile gcc test.c -o test, I get the following error:

/tmp/ccb7O0eh.o: In function `main':
test.c:(.text+0xa): undefined reference to `call_function_declared_in_the_header_file'
collect2: error: ld returned 1 exit status

I don't know why. I am not good at the C language. So how can I fix it?

`call_function_defined_in_the_header_file()` is probably just *declared* (not *defined*) in `xx/xx.h`. — JFMR, Jan 07 '18 at 14:17
Add an option to tell the linker to look for the library. Since you library names are not `libxx.a` and `libxx.so`, you’ll have to supply their path. Better to rename them so you can use `-lxx`. — Jonathan Leffler, Jan 07 '18 at 14:20
Use `-L` to specify the library path and `-l` to name the library in that path to search (at least, those are the gcc options). — Tom Karzes, Jan 07 '18 at 14:21
@jonathan-leffler[https://stackoverflow.com/users/15168/jonathan-leffler] writing wrong,I have edit it again. They are sure named `libxx.a` and `libxx.so`. — ChengTao, Jan 07 '18 at 14:23
So add `-lxx` to the command line that links the program — at the end, after all the object (and/or source) files listed on the command line. — Jonathan Leffler, Jan 07 '18 at 14:24
@JonathanLeffler If I use cmake,so how can I set the option in CMakeLists.txt? — ChengTao, Jan 07 '18 at 15:07

ralf htp · Answer 1 · 2018-01-07T14:32:31.227

1

you have to link against the library, i.e. if you want to include <math.h> ( libm.so / libm.a ) you have to link against :

gcc program.c -o program -lm where the -lm invokes the linking

see http://www.network-theory.co.uk/docs/gccintro/gccintro_17.html,

https://www.rapidtables.com/code/linux/gcc/gcc-l.html

compiling always involves the compiler and the linker

edited Jan 07 '18 at 14:32

answered Jan 07 '18 at 14:23

ralf htp

9,149
4
22
34

gcc : undefined reference to 'function'

1 Answers1