zlib.h problem

jnusa · 01-13-2005, 04:17 AM

I'm trying to use the zlib library and it seems like it is included and found (when I compile the c file using the zlib.h, there's no error). Never the less, when I link my program I get a undefined reference, to the function I use i zlib (compress2).

Code:

//gzip_interface.c

#include <string.h>
#include <stdlib.h>
#include <linux/zlib.h>
#include "gzip_interface.h"

int compress_buf(char *dst, char *src, unsigned short int level )
{
	int size = strlen(src);
	int return_size = 0;
	dst = malloc(size);
	return_size = compress2(dst, size, src, size, level);
	return 0;
	
}

//gzip_interface.h

#ifndef GZIP_INTERFACE
#define GZIP_INTERFACE

int compress_buf(char *dst, char *src, unsigned short int level);
#endif

How can this be? I've search for zlib, and it is located in /usr/include and also in /usr/include/linux. I've tried including it like this: #include <zlib.h>, but it's the same problem. I'm using Anjuta (on ProMepis 2005.b04), and I've tried adding the library manually, so it links with -lzlib option.. that didn't work either (Second Q: How do you know when it need to be included manually when linking? .. pthread needs to : -lpthread ??).
Any help will be greatly appriciated.

Regards jnusa

__J · 01-13-2005, 06:40 AM

I believe to manually link zlib its:

-lz

jnusa · 01-13-2005, 06:52 AM

Yeah.. found out after 1½h

. Thanks for the reply anyway _.|

Inunu · 01-13-2005, 08:37 PM

Hi Jnusa.

You need to manually link using '-lz' as __J said. For any shared library in your /usr/lib say libxxx-yyy.so.* you can always do -lxxx-yyy, just the section between "lib" and ".so.whatever version". E.g. for libglib-2.0.so.0.400.8, use -lglib-2.0.

The other thing is that the destination size of zlib needs to be a pointer to int, so that the actually byte count filled into destination after (un)compression can be passed to its caller. In the sample you seem to pass the value directly into compress2 (the 2nd parameter).

Code:

#include <stdio.h>
#include <zlib.h>

int main(int argc, char *argv[]){
        char *str="This is a string of test for libz compression.";
        char bufferc[1024];
        char bufferu[1024];
        unsigned long sizec=1024, sizeu=1024;
        int retc=0, retu=0;

        retc=compress2(bufferc, &sizec, str, strlen(str), 9); /* compress str to bufferc */
        bufferc[sizec]='\0';
        retu=uncompress(bufferu, &sizeu, bufferc, sizec); /* uncompress bufferc to bufferu */
        bufferu[sizeu]='\0';
        printf("orig=%s\ncompressed(%d,%d)=%s\nuncompressed(%d,%d)=%s\n",
                str, retc, sizec, bufferc, retu, sizeu, bufferu);

        return 0;
}

linux/tmp$ gcc -o gztest gztest.c -lz
linux/tmp$ ./gztest
orig=This is a string of test for libz compression.
compressed(0,52)=x\uffff
\u572e,V
uncompressed(0,46)=This is a string of test for libz compression.

jnusa · 01-14-2005, 12:47 AM

OK, appriciate it!