test.c:(.text+0x36): undefined reference to `md5_file'

Question

I installed polarssl:

make
sudo make install

tried to compile very simple file, named test.c:

#include <stdio.h>
#include "polarssl/md5.h"

int main(int argc, char * argv[])
{
  int i;
  for (i=1;i<1;i++)
  {
    char res[16];
    if (md5_file("file.txt",res) == 0)
    {
      int count;
      for (count=0;count<16;count++)
        printf("%02x",res[count]);
      printf("n");
    }
  }
  return 0;
}

Compiled it like this:

gcc -lpolarssl test.c -I /usr/local/include/polarssl/

but it shows me:

/tmp/cczptlsk.o: In function `main':
test.c:(.text+0x36): undefined reference to `md5_file'
collect2: ld returned 1 exit status

whats the problem, how to fix it? I know for 100% that polarssl files are in /usr/local/include/polarssl/

You only put the included statement in " " if you start looking in the local directory. Is the program running from the include folder? — KrisSodroski, Jun 27 '13 at 17:08
@Magn3s1um: nope but even if I change " " to < > it gives the same error anyway — yak, Jun 27 '13 at 17:10
`/usr/local/include` sounds unusual for libs, but may be libpolarssl,a doesn't contain a definition for this method. Did you check the contents of the lib, e.g. with nm? — πάντα ῥεῖ, Jun 27 '13 at 17:11
@yak Its the linking that was failing. So, it should has something to do with the linking flags. — Mahesh, Jun 27 '13 at 17:12

score 4 · Accepted Answer · answered Jun 27 '13 at 17:13

4

The compiler will attempt to complete linkage in the order the objects or files are presented. In this case, since you had put -lpolarssl first, there were no unresolved symbols needed from that library, so nothing got linked in.

Putting -lpolarssl last lets the compiler resolve unresolved symbols from your source file from that library.

answered Jun 27 '13 at 17:13

jxh

69,070
8
110
193

thank you so much, wonderful explanation, now I can fully understand it, cheers:) – yak Jun 27 '13 at 17:28

Yohan Danvin · Answer 2 · 2013-06-27T17:28:19.783

2

Includes are fine.

But linking is wrong. Try to put the -lpolarssl last in the linker command.

Then add a -L if libpolarssl.a is not found by the linker to point it to the right location.

edited Jun 27 '13 at 17:28

answered Jun 27 '13 at 17:11

Yohan Danvin

885
6
13

So should it be just `gcc test.c -lpolarssl` or `gcc test.c -L /usr/local/include/polarssl/ -lpolarssl `? this works too – yak Jun 27 '13 at 17:16
2

You can add `-I /usr/local/include/polarssl/` but only if you want to be able to write `#include ` instead of `#include `, which is probably not necessary. Careful, `-L` is for specifying additional locations for compiled libs, as opposed to `-I` which is for addition locations for headers (#includes). – Yohan Danvin Jun 27 '13 at 17:19

test.c:(.text+0x36): undefined reference to `md5_file'

2 Answers2