Question

so I’m using the zlib package on Ubuntu. I’m trying to figure out how to use gzopen and gzread correctly, this is what I have so far

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

#define NUM_BUFFERS 8
#define BUFFER_LENGTH 1024

char buf[BUFFER_LENGTH];
int main(int argc, const char* argv[])
{
    int status;
    gzFile file;
    file = gzopen("beowulf.txt", "w");
    int counter = 0; /*when the counter reachers BUFFERS_FULL, stop*/
    if(file == NULL)
    {
        printf("COULD NOT OPEN FILE\n");
        return 1;
    }
    while(counter < NUM_BUFFERS)
    {
        status = gzread(file, buf, BUFFER_LENGTH - 2);
        printf("STATUS: %d\n", status);
        buf[BUFFER_LENGTH - 1] = "\0";
        printf("%s\n", buf);
        counter++;
    }
    gzclose(file);
    printf("STATUS: %d\n", status);
    return 0;
}

The gzread("STATUS: %d\n",status); returns -2, and I have no clue why. Any help would be appreciated.

Answer 1

Mode "w" indicates that you are preparing to create a new archive:

file = gzopen("beowulf.txt", "w");

You’ve just truncated the file to zero length.

Also, you should use the binary mode flag: "wb" or "rb".

Also, it’s a bit weird that your supposed .gz-archive has an extension .txt.

Read the docs, docs rule. 🙂