Name

Library

Libz.lib

Synopsis

#include <zlib.h>
z_off_t gzseek(gzFile file, z_off_t offset, int whence);

On success, gzseek() shall return the resulting offset in the file expressed as a byte position in the uncompressed data stream. On error, gzseek() shall return -1, and may set the error value for file accordingly.

Detailed Description

The gzseek() function shall set the file-position indicator for the compressed file stream file. The file-position indicator controls where the next read or write operation on the compressed file stream shall take place. The offset indicates a byte offset in the uncompressed data. The whence parameter may be one of:

If the file is open for writing, the new offset must be greater than or equal to the current offset. In this case, gzseek() shall compress a sequence of null bytes to fill the gap from the previous offset to the new offset.

#include <stdio.h>
#include <zlib.h>
  
void Gzseek( )
{    
    Byte *compr, *uncompr;
    uLong comprLen = 20*sizeof(int); 
    uLong uncomprLen = comprLen;
    static const char* myVersion = ZLIB_VERSION;
    const char hello[] = "hello, hello!";                 
    compr    = (Byte*)calloc((uInt)comprLen, 1);
    uncompr  = (Byte*)calloc((uInt)uncomprLen, 1);
    compress(compr, &comprLen, (const Bytef*)hello, len);
    
    int len = (int)strlen(hello)+1;
    gzFile file;
    file = gzopen(TESTFILE, "wb");
    gzputc(file, 'h');
    gzputs(file, "ello");
    
    gzseek(file, 1L, SEEK_CUR); /* add one zero byte */
    free(compr);
    free(uncompr);
}

On error, gzseek() shall return -1. The following conditions shall always result in an error:

• file is NULL

• file does not represent an open compressed file stream.

• file refers to a compressed file stream that is open for writing, and the newly computed offset is less than the current offset.
  

• The newly computed offset is less than zero.

• whence is not one of the supported values.