Name

deflateInit_ — Initializes the compression system.

Library

Libz.lib

Synopsis

#include <zlib.h>

int deflateInit_(z_streamp stream, int level, const char * version, int stream_size);

Return Value

On success, the deflateInit_() function shall return Z_OK. Otherwise, deflateInit_() shall return a value as described below to indicate the error.

Detailed Description

The deflateInit_() function shall initialize the compression system. On entry, stream shall refer to a user supplied z_stream object (a z_stream_s structure). The following fields shall be set on entry:

`zalloc`	a pointer to an alloc_func function, used to allocate state information. If this is `NULL`, a default allocation function will be used.
`zfree`	a pointer to a free_func function, used to free memory allocated by the `zalloc` function. If this is `NULL` a default free function will be used.
`opaque`	If `alloc_func` is not `NULL`, `opaque` is a user supplied pointer to data that will be passed to the `alloc_func` and `free_func` functions.

If the version requested is not compatible with the version implemented, or if the size of the z_stream_s structure provided in stream_size does not match the size in the library implementation, deflateInit_() shall fail, and return Z_VERSION_ERROR.

The level supplied shall be a value between 0 and 9, or the value Z_DEFAULT_COMPRESSION. A level of 1 requests the highest speed, while a level of 9 requests the highest compression. A level of 0 indicates that no compression should be used, and the output shall be the same as the input.

The deflateInit_() function is not in the source standard; it is only in the binary standard. Source applications should use the deflateInit() macro.

The deflateInit_() function is equivalent to deflateInit2_(stream, level, Z_DEFLATED, MAX_WBITS, DEF_MEM_LEVEL, Z_DEFAULT_STRATEGY, version, stream_size).

Examples

To initialize the compression system:

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

void DeflateInit_( )

{   
    z_stream stream; 
    uLong sourceLen = (uLong)strlen(hello)+1; 
    Byte *compr; 
    uLong comprLen = 10*sizeof(int); 
    uLong uncomprLen = comprLen; 
    compr    = (Byte*)calloc((uInt)comprLen, 1); 
    const char hello[] = "hello, hello!"; 
    stream.zalloc = (alloc_func)0; 
    stream.zfree = (free_func)0; 
    stream.opaque = (voidpf)0;

    deflateInit_(&stream, Z_DEFAULT_COMPRESSION,  zlibVersion(), sizeof(z_stream)); 
    deflateEnd(&stream); 
    free(compr);   
}

Errors

On error, deflateInit_() shall return one of the following error indicators:

`Z_STREAM_ERROR`	Invalid parameter.
`Z_MEM_ERROR`	Insufficient memory available.
`Z_VERSION_ERROR`	The version requested is not compatible with the library version, or the z_stream size differs from that used by the library.

In addition, the msg field of the stream may be set to an error message.

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