Question

(I’m on Windows.)

I’m testing a DLL I have compiled (libsox) with a C program which looks this way:

#include <stdio.h>
#include "sox.h"

int main(void) {
    char const * versionText = sox_version();
    printf(versionText);
    return 0;
}

The function that is defined in the DLL has the following prototype in sox.h (something of this contains cdecl):

LSX_RETURN_VALID_Z LSX_RETURN_PURE
char const *
LSX_API
sox_version(void);

Here’s the problem: When I try to build the file with gcc -lsox -o test.exe test.c I get the following error:

C:\DOKUME~1\ADMINI~1\LOKALE~1\Temp\ccSS2h2z.o:test.c:(.text+0xf): undefined reference to `sox_version'
collect2: ld returned 1 exit status

A word to -lsox: I have the library file “libsox.dll.a” in MinGW’s lib folder. If I write -lsoxnonsense, then it says there is no library. That means in the shown case it finds the library. So why doesn’t it want to create a link.

Answer 1

gcc -lsox -o test.exe test.c

You have to put your source file first:

gcc test.c -lsox -o test.exe

It is because the linker goes through the input files in order, finding undefined references and satisfying references that it saw before. So in your command line, it reads libsox.a (or something like that), finds undefined references (there would be none). Then, it goes to your test.c, finds undefined references in there, but there are no further libraries to satisfy them.

See this answer for more info.