NAME
zlib —
general purpose compression
library
SYNOPSIS
#include <zlib.h>
Basic functions
const char *
zlibVersion(
void);
int
deflateInit(
z_streamp
strm,
int level);
int
deflate(
z_streamp
strm,
int flush);
int
deflateEnd(
z_streamp
strm);
int
inflateInit(
z_streamp
strm);
int
inflate(
z_streamp
strm,
int flush);
int
inflateEnd(
z_streamp
strm);
Advanced functions
int
deflateInit2(
z_streamp
strm,
int level,
int method,
int windowBits,
int memLevel,
int strategy);
int
deflateSetDictionary(
z_streamp
strm,
const Bytef
*dictionary,
uInt
dictLength);
int
deflateCopy(
z_streamp
dest,
z_streamp
source);
int
deflateReset(
z_streamp
strm);
int
deflateParams(
z_streamp
strm,
int level,
int strategy);
int
inflateInit2(
z_streamp
strm,
int
windowBits);
int
inflateSetDictionary(
z_streamp
strm,
const Bytef
*dictionary,
uInt
dictLength);
int
inflateSync(
z_streamp
strm);
int
inflateReset(
z_streamp
strm);
Utility functions
typedef voidp gzFile ;
int
compress(
Bytef
*dest,
uLongf
*destLen,
const Bytef
*source,
uLong
sourceLen);
int
compress2(
Bytef
*dest,
uLongf
*destLen,
const Bytef
*source,
uLong
sourceLen,
int
level);
int
uncompress(
Bytef
*dest,
uLongf
*destLen,
const Bytef
*source,
uLong
sourceLen);
gzFile
gzopen(
const char
*path,
const char
*mode);
gzFile
gzdopen(
int
fd,
const char
*mode);
int
gzsetparams(
gzFile
file,
int level,
int strategy);
int
gzread(
gzFile
file,
voidp buf,
unsigned len);
int
gzwrite(
gzFile
file,
const voidp
buf,
unsigned len);
int
gzprintf(
gzFile
file,
const char
*format,
...);
int
gzputs(
gzFile
file,
const char *s);
char *
gzgets(
gzFile
file,
char *buf,
int len);
int
gzputc(
gzFile
file,
int c);
int
gzgetc(
gzFile
file);
int
gzflush(
gzFile
file,
int flush);
z_off_t
gzseek(
gzFile
file,
z_off_t offset,
int whence);
int
gzrewind(
gzFile
file);
z_off_t
gztell(
gzFile
file);
int
gzeof(
gzFile
file);
int
gzclose(
gzFile
file);
const char *
gzerror(
gzFile
file,
int *errnum);
Checksum functions
uLong
adler32(
uLong
adler,
const Bytef
*buf,
uInt len);
uLong
crc32(
uLong
crc,
const Bytef
*buf,
uInt len);
DESCRIPTION
This manual page describes the
zlib general purpose
compression library, version 1.1.4.
The
zlib compression library provides in-memory compression
and decompression functions, including integrity checks of the uncompressed
data. This version of the library supports only one compression method
(deflation) but other algorithms will be added later and will have the same
stream interface.
Compression can be done in a single step if the buffers are large enough (for
example if an input file is mmap'ed), or can be done by repeated calls of the
compression function. In the latter case, the application must provide more
input and/or consume the output (providing more output space) before each
call.
The library also supports reading and writing files in
gzip(1) (.gz) format with an
interface similar to that of
stdio(3).
The library does not install any signal handler. The decoder checks the
consistency of the compressed data, so the library should never crash even in
case of corrupted input.
The functions within the library are divided into the following sections:
- Basic functions
- Advanced functions
- Utility functions
- Checksum functions
BASIC FUNCTIONS
-
-
- const char
* zlibVersion(void);
-
The application can compare zlibVersion() and
ZLIB_VERSION
for consistency. If the first
character differs, the library code actually used is not compatible with
the <zlib.h> header file used by
the application. This check is automatically made by
deflateInit() and inflateInit().
-
-
- int
deflateInit(z_streamp strm,
int level);
-
The deflateInit() function initializes the internal stream
state for compression. The fields zalloc,
zfree, and opaque must be
initialized before by the caller. If zalloc and
zfree are set to
Z_NULL
,
deflateInit() updates them to use default allocation
functions.
The compression level must be Z_DEFAULT_COMPRESSION
,
or between 0 and 9: 1 gives best speed, 9 gives best compression, 0 gives
no compression at all (the input data is simply copied a block at a time).
Z_DEFAULT_COMPRESSION
requests a default compromise
between speed and compression (currently equivalent to level 6).
deflateInit() returns Z_OK
if
successful, Z_MEM_ERROR
if there was not enough
memory, Z_STREAM_ERROR
if level is not a valid
compression level, Z_VERSION_ERROR
if the
zlib library version (zlib_version) is incompatible with
the version assumed by the caller (ZLIB_VERSION).
msg is set to null if there is no error message.
deflateInit() does not perform any compression: this
will be done by deflate().
-
-
- int
deflate(z_streamp strm,
int flush);
-
deflate() compresses as much data as possible, and stops
when the input buffer becomes empty or the output buffer becomes full. It
may introduce some output latency (reading input without producing any
output) except when forced to flush.
The detailed semantics are as follows. deflate() performs
one or both of the following actions:
Compress more input starting at next_in and update
next_in and avail_in
accordingly. If not all input can be processed (because there is not
enough room in the output buffer), next_in and
avail_in are updated and processing will resume at
this point for the next call to deflate().
Provide more output starting at next_out and update
next_out and avail_out
accordingly. This action is forced if the parameter
flush is non-zero. Forcing
flush frequently degrades the compression ratio, so
this parameter should be set only when necessary (in interactive
applications). Some output may be provided even if
flush is not set.
Before the call to deflate(), the application should
ensure that at least one of the actions is possible, by providing more
input and/or consuming more output, and updating
avail_in or avail_out
accordingly; avail_out should never be zero before
the call. The application can consume the compressed output when it wants,
for example when the output buffer is full (avail_out == 0), or after each
call to deflate(). If deflate()
returns
Z_OK
and with zero
avail_out, it must be called again after making room
in the output buffer because there might be more output pending.
If the parameter flush is set to
Z_SYNC_FLUSH
, all pending output is flushed to the
output buffer and the output is aligned on a byte boundary, so that the
decompressor can get all input data available so far. (In particular,
avail_in is zero after the call if enough output
space has been provided before the call.) Flushing may degrade compression
for some compression algorithms and so it should be used only when
necessary.
If flush is set to
Z_FULL_FLUSH
, all output is flushed as with
Z_SYNC_FLUSH
, and the compression state is reset
so that decompression can restart from this point if previous compressed
data has been damaged or if random access is desired. Using
Z_FULL_FLUSH
too often can seriously degrade the
compression.
If deflate() returns with avail_out == 0, this function
must be called again with the same value of the flush parameter and more
output space (updated avail_out), until the flush is
complete (deflate() returns with non-zero
avail_out).
If the parameter flush is set to
Z_FINISH
, pending input is processed, pending
output is flushed and deflate() returns with
Z_STREAM_END
if there was enough output space; if
deflate() returns with Z_OK
,
this function must be called again with Z_FINISH
and more output space (updated avail_out but no more
input data, until it returns with Z_STREAM_END
or
an error. After deflate() has returned
Z_STREAM_END
, the only possible operations on the
stream are deflateReset() or
deflateEnd().
Z_FINISH
can be used immediately after
deflateInit() if all the compression is to be done in a
single step. In this case, avail_out must be at
least 0.1% larger than avail_in plus 12 bytes. If
deflate() does not return
Z_STREAM_END
, then it must be called again as
described above.
deflate() sets strm->adler to the Adler-32 checksum of
all input read so far (that is, total_in bytes).
deflate() may update data_type if it
can make a good guess about the input data type (Z_ASCII or Z_BINARY). If
in doubt, the data is considered binary. This field is only for
information purposes and does not affect the compression algorithm in any
manner.
deflate() returns Z_OK
if some
progress has been made (more input processed or more output produced),
Z_STREAM_END
if all input has been consumed and
all output has been produced (only when flush is set
to Z_FINISH
),
Z_STREAM_ERROR
if the stream state was
inconsistent (for example, if next_in or
next_out was NULL
),
Z_BUF_ERROR
if no progress is possible (for
example, avail_in or avail_out
was zero).
-
-
- int
deflateEnd(z_streamp strm);
-
All dynamically allocated data structures for this stream are freed. This
function discards any unprocessed input and does not flush any pending
output.
deflateEnd() returns
Z_OK
if
successful, Z_STREAM_ERROR
if the stream state was
inconsistent, Z_DATA_ERROR
if the stream was freed
prematurely (some input or output was discarded). In the error case,
msg may be set but then points to a static string
(which must not be deallocated).
-
-
- int
inflateInit(z_streamp strm);
- The inflateInit() function initializes
the internal stream state for decompression. The fields
next_in, avail_in,
zalloc, zfree, and
opaque must be initialized before by the caller. If
next_in is not
Z_NULL
and
avail_in is large enough (the exact value depends on
the compression method), inflateInit() determines the
compression method from the zlib header and allocates
all data structures accordingly; otherwise the allocation will be deferred
to the first call to inflate(). If
zalloc and zfree are set to
Z_NULL
, inflateInit() updates
them to use default allocation functions.
inflateInit() returns Z_OK
if
successful, Z_MEM_ERROR
if there was not enough
memory, Z_VERSION_ERROR
if the
zlib library version is incompatible with the version
assumed by the caller. msg is set to null if there
is no error message. inflateInit() does not perform any
decompression apart from reading the zlib header if
present: this will be done by inflate(). (So
next_in and avail_in may be
modified, but next_out and
avail_out are unchanged.)
-
-
- int
inflate(z_streamp strm,
int flush);
- inflate() decompresses as much data as
possible, and stops when the input buffer becomes empty or the output
buffer becomes full. It may introduce some output latency (reading input
without producing any output) except when forced to flush.
The detailed semantics are as follows. inflate() performs
one or both of the following actions:
Decompress more input starting at next_in and update
next_in and avail_in
accordingly. If not all input can be processed (because there is not
enough room in the output buffer), next_in is
updated and processing will resume at this point for the next call to
inflate().
Provide more output starting at next_out and update
next_out and avail_out
accordingly. inflate() provides as much output as
possible, until there is no more input data or no more space in the output
buffer (see below about the flush parameter).
Before the call to inflate(), the application should
ensure that at least one of the actions is possible, by providing more
input and/or consuming more output, and updating the next_* and avail_*
values accordingly. The application can consume the uncompressed output
when it wants, for example when the output buffer is full (avail_out ==
0), or after each call to inflate(). If
inflate() returns
Z_OK
and with
zero avail_out, it must be called again after making
room in the output buffer because there might be more output pending.
If the parameter flush is set to
Z_SYNC_FLUSH
, inflate() flushes
as much output as possible to the output buffer. The flushing behavior of
inflate() is not specified for values of the flush
parameter other than Z_SYNC_FLUSH
and
Z_FINISH
, but the current implementation actually
flushes as much output as possible anyway.
inflate() should normally be called until it returns
Z_STREAM_END
or an error. However if all
decompression is to be performed in a single step (a single call to
inflate), the parameter flush should be set to
Z_FINISH
. In this case all pending input is
processed and all pending output is flushed;
avail_out must be large enough to hold all the
uncompressed data. (The size of the uncompressed data may have been saved
by the compressor for this purpose.) The next operation on this stream
must be inflateEnd() to deallocate the decompression
state. The use of Z_FINISH
is never required, but
can be used to inform inflate() that a faster routine
may be used for the single inflate() call.
If a preset dictionary is needed at this point (see
inflateSetDictionary() below),
inflate() sets strm->adler to the Adler-32 checksum
of the dictionary chosen by the compressor and returns
Z_NEED_DICT
; otherwise it sets strm->adler to
the Adler-32 checksum of all output produced so far (that is,
total_out bytes) and returns
Z_OK
, Z_STREAM_END
, or an
error code as described below. At the end of the stream,
inflate() checks that its computed Adler-32 checksum is
equal to that saved by the compressor and returns
Z_STREAM_END
only if the checksum is correct.
inflate() returns Z_OK
if some
progress has been made (more input processed or more output produced),
Z_STREAM_END
if the end of the compressed data has
been reached and all uncompressed output has been produced,
Z_NEED_DICT
if a preset dictionary is needed at
this point, Z_DATA_ERROR
if the input data was
corrupted (input stream not conforming to the zlib
format or incorrect Adler-32 checksum),
Z_STREAM_ERROR
if the stream structure was
inconsistent (for example, if next_in or
next_out was NULL
),
Z_MEM_ERROR
if there was not enough memory,
Z_BUF_ERROR
if no progress is possible or if there
was not enough room in the output buffer when
Z_FINISH
is used. In the
Z_DATA_ERROR
case, the application may then call
inflateSync() to look for a good compression block.
-
-
- int
inflateEnd(z_streamp strm);
- All dynamically allocated data structures for this stream
are freed. This function discards any unprocessed input and does not flush
any pending output.
inflateEnd() returns
Z_OK
if
successful, or Z_STREAM_ERROR
if the stream state
was inconsistent. In the error case, msg may be set
but then points to a static string (which must not be deallocated).
ADVANCED FUNCTIONS
The following functions are needed only in some special applications.
-
-
- int
deflateInit2(z_streamp strm,
int level, int method,
int windowBits, int memLevel,
int strategy);
-
This is another version of deflateInit() with more
compression options. The fields next_in,
zalloc, zfree, and
opaque must be initialized before by the caller.
The method parameter is the compression method. It
must be
Z_DEFLATED
in this version of the library.
The windowBits parameter is the base two logarithm of
the window size (the size of the history buffer). It should be in the
range 8..15 for this version of the library. Larger values of this
parameter result in better compression at the expense of memory usage. The
default value is 15 if deflateInit() is used instead.
The memLevel parameter specifies how much memory
should be allocated for the internal compression state. memLevel=1 uses
minimum memory but is slow and reduces compression ratio; memLevel=9 uses
maximum memory for optimal speed. The default value is 8. See
<zconf.h> for total memory usage
as a function of windowBits and
memLevel.
The strategy parameter is used to tune the compression
algorithm. Use the value Z_DEFAULT_STRATEGY
for
normal data; Z_FILTERED
for data produced by a
filter (or predictor); or Z_HUFFMAN_ONLY
to force
Huffman encoding only (no string match). Filtered data consists mostly of
small values with a somewhat random distribution. In this case, the
compression algorithm is tuned to compress them better. The effect of
Z_FILTERED
is to force more Huffman coding and
less string matching; it is somewhat intermediate between
Z_DEFAULT
and
Z_HUFFMAN_ONLY
. The strategy
parameter only affects the compression ratio but not the correctness of
the compressed output, even if it is not set appropriately.
deflateInit2() returns Z_OK
if
successful, Z_MEM_ERROR
if there was not enough
memory, Z_STREAM_ERROR
if a parameter is invalid
(such as an invalid method). msg is set to null if
there is no error message. deflateInit2() does not
perform any compression: this will be done by
deflate().
-
-
- int
deflateSetDictionary(z_streamp strm,
const Bytef *dictionary, uInt
dictLength);
-
Initializes the compression dictionary from the given byte sequence without
producing any compressed output. This function must be called immediately
after deflateInit(), deflateInit2(),
or deflateReset(), before any call to
deflate(). The compressor and decompressor must use
exactly the same dictionary (see
inflateSetDictionary()).
The dictionary should consist of strings (byte sequences) that are likely to
be encountered later in the data to be compressed, with the most commonly
used strings preferably put towards the end of the dictionary. Using a
dictionary is most useful when the data to be compressed is short and can
be predicted with good accuracy; the data can then be compressed better
than with the default empty dictionary.
Depending on the size of the compression data structures selected by
deflateInit() or deflateInit2(), a
part of the dictionary may in effect be discarded, for example if the
dictionary is larger than the window size in deflate()
or deflate2(). Thus the strings most likely to be useful
should be put at the end of the dictionary, not at the front.
Upon return of this function, strm->adler is set to the Adler-32 value of
the dictionary; the decompressor may later use this value to determine
which dictionary has been used by the compressor. (The Adler-32 value
applies to the whole dictionary even if only a subset of the dictionary is
actually used by the compressor.)
deflateSetDictionary() returns
Z_OK
if successful, or
Z_STREAM_ERROR
if a parameter is invalid (such as
NULL dictionary) or the stream state is inconsistent (for example if
deflate() has already been called for this stream or if
the compression method is bsort). deflateSetDictionary()
does not perform any compression: this will be done by
deflate().
-
-
- int
deflateCopy(z_streamp dest,
z_streamp source);
-
The deflateCopy() function sets the destination stream as
a complete copy of the source stream.
This function can be useful when several compression strategies will be
tried, for example when there are several ways of pre-processing the input
data with a filter. The streams that will be discarded should then be
freed by calling deflateEnd(). Note that
deflateCopy() duplicates the internal compression state
which can be quite large, so this strategy is slow and can consume lots of
memory.
deflateCopy() returns
Z_OK
if
successful, Z_MEM_ERROR
if there was not enough
memory, Z_STREAM_ERROR
if the source stream state
was inconsistent (such as zalloc being NULL).
msg is left unchanged in both source and
destination.
-
-
- int
deflateReset(z_streamp strm);
-
This function is equivalent to deflateEnd() followed by
deflateInit(), but does not free and reallocate all the
internal compression state. The stream will keep the same compression
level and any other attributes that may have been set by
deflateInit2().
deflateReset() returns
Z_OK
if
successful, or Z_STREAM_ERROR
if the source stream
state was inconsistent (such as zalloc or
state being NULL).
-
-
- int
deflateParams(z_streamp strm,
int level, int strategy);
-
The deflateParams() function dynamically updates the
compression level and compression strategy. The interpretation of level
and strategy is as in deflateInit2(). This can be used
to switch between compression and straight copy of the input data, or to
switch to a different kind of input data requiring a different strategy.
If the compression level is changed, the input available so far is
compressed with the old level (and may be flushed); the new level will
take effect only at the next call to deflate().
Before the call to deflateParams(), the stream state must
be set as for a call to deflate(), since the currently
available input may have to be compressed and flushed. In particular,
strm->avail_out must be non-zero.
deflateParams() returns
Z_OK
if
successful, Z_STREAM_ERROR
if the source stream
state was inconsistent or if a parameter was invalid, or
Z_BUF_ERROR
if strm->avail_out was zero.
-
-
- int
inflateInit2(z_streamp strm,
int windowBits);
-
This is another version of inflateInit() with an extra
parameter. The fields next_in,
avail_in, zalloc,
zfree, and opaque must be
initialized before by the caller.
The windowBits parameter is the base two logarithm of
the maximum window size (the size of the history buffer). It should be in
the range 8..15 for this version of the library. The default value is 15
if inflateInit() is used instead. If a compressed stream
with a larger window size is given as input, inflate()
will return with the error code
Z_DATA_ERROR
instead of trying to allocate a larger window.
inflateInit2() returns Z_OK
if
successful, Z_MEM_ERROR
if there was not enough
memory, Z_STREAM_ERROR
if a parameter is invalid
(such as a negative memLevel).
msg is set to null if there is no error message.
inflateInit2() does not perform any decompression apart
from reading the zlib header if present: this will be
done by inflate(). (So next_in and
avail_in may be modified, but
next_out and avail_out are
unchanged.)
-
-
- int
inflateSetDictionary(z_streamp strm,
const Bytef *dictionary, uInt
dictLength);
-
Initializes the decompression dictionary from the given uncompressed byte
sequence. This function must be called immediately after a call to
inflate() if this call returned
Z_NEED_DICT
. The dictionary chosen by the
compressor can be determined from the Adler-32 value returned by this call
to inflate(). The compressor and decompressor must use
exactly the same dictionary (see
deflateSetDictionary()).
inflateSetDictionary() returns
Z_OK
if successful,
Z_STREAM_ERROR
if a parameter is invalid (such as
NULL dictionary) or the stream state is inconsistent,
Z_DATA_ERROR
if the given dictionary doesn't match
the expected one (incorrect Adler-32 value).
inflateSetDictionary() does not perform any
decompression: this will be done by subsequent calls of
inflate().
-
-
- int
inflateSync(z_streamp strm);
-
Skips invalid compressed data until a full flush point (see above the
description of deflate() with
Z_FULL_FLUSH
) can be found, or until all available
input is skipped. No output is provided.
inflateSync() returns Z_OK
if a
full flush point has been found, Z_BUF_ERROR
if no
more input was provided, Z_DATA_ERROR
if no flush
point has been found, or Z_STREAM_ERROR
if the
stream structure was inconsistent. In the success case, the application
may save the current value of total_in which
indicates where valid compressed data was found. In the error case, the
application may repeatedly call inflateSync(), providing
more input each time, until success or end of the input data.
-
-
- int
inflateReset(z_streamp strm);
-
This function is equivalent to inflateEnd() followed by
inflateInit(), but does not free and reallocate all the
internal decompression state. The stream will keep attributes that may
have been set by inflateInit2().
inflateReset() returns
Z_OK
if
successful, or Z_STREAM_ERROR
if the source stream
state was inconsistent (such as zalloc or
state being NULL).
UTILITY FUNCTIONS
The following utility functions are implemented on top of the basic
stream-oriented functions. To simplify the interface, some default options are
assumed (compression level and memory usage, standard memory allocation
functions). The source code of these utility functions can easily be modified
if you need special options.
-
-
- int
compress(Bytef *dest,
uLongf *destLen, const Bytef
*source, uLong sourceLen);
-
The compress() function compresses the source buffer into
the destination buffer. sourceLen is the byte length
of the source buffer. Upon entry, destLen is the
total size of the destination buffer, which must be at least 0.1% larger
than sourceLen plus 12 bytes. Upon exit,
destLen is the actual size of the compressed buffer.
This function can be used to compress a whole file at once if the input
file is mmap'ed.
compress() returns
Z_OK
if
successful, Z_MEM_ERROR
if there was not enough
memory, or Z_BUF_ERROR
if there was not enough
room in the output buffer.
-
-
- int
compress2(Bytef *dest,
uLongf *destLen, const Bytef
*source, uLong sourceLen, int
level);
-
The compress2() function compresses the source buffer into
the destination buffer. The level parameter has the
same meaning as in deflateInit().
sourceLen is the byte length of the source buffer.
Upon entry, destLen is the total size of the
destination buffer, which must be at least 0.1% larger than
sourceLen plus 12 bytes. Upon exit,
destLen is the actual size of the compressed buffer.
compress2() returns
Z_OK
if
successful, Z_MEM_ERROR
if there was not enough
memory, Z_BUF_ERROR
if there was not enough room
in the output buffer, or Z_STREAM_ERROR
if the
level parameter is invalid.
-
-
- int
uncompress(Bytef *dest,
uLongf *destLen, const Bytef
*source, uLong sourceLen);
-
The uncompress() function decompresses the source buffer
into the destination buffer. sourceLen is the byte
length of the source buffer. Upon entry, destLen is
the total size of the destination buffer, which must be large enough to
hold the entire uncompressed data. (The size of the uncompressed data must
have been saved previously by the compressor and transmitted to the
decompressor by some mechanism outside the scope of this compression
library.) Upon exit, destLen is the actual size of
the compressed buffer. This function can be used to decompress a whole
file at once if the input file is mmap'ed.
uncompress() returns
Z_OK
if
successful, Z_MEM_ERROR
if there was not enough
memory, Z_BUF_ERROR
if there was not enough room
in the output buffer, or Z_DATA_ERROR
if the input
data was corrupted.
-
-
- gzFile
gzopen(const char *path,
const char *mode);
-
The gzopen() function opens a gzip (.gz) file for reading
or writing. The mode parameter is as in
fopen(3) (“rb” or
“wb”) but can also include a compression level
(“wb9”) or a strategy: ‘f’ for filtered data, as
in “wb6f”; ‘h’ for Huffman only compression, as in
“wb1h”. (See the description of
deflateInit2() for more information about the strategy
parameter.)
gzopen() can be used to read a file which is not in gzip
format; in this case gzread() will directly read from
the file without decompression.
gzopen() returns
NULL
if the file
could not be opened or if there was insufficient memory to allocate the
(de)compression state; errno can be checked to distinguish the two cases
(if errno is zero, the zlib error is
Z_MEM_ERROR
).
-
-
- gzFile
gzdopen(int fd,
const char *mode);
-
The gzdopen() function associates a gzFile with the file
descriptor fd. File descriptors are obtained from
calls like open(2),
dup(2),
creat(3),
pipe(2), or
fileno(3) (if the file has
been previously opened with
fopen(3)). The
mode parameter is as in gzopen().
The next call to gzclose() on the returned gzFile will
also close the file descriptor fd, just like fclose(fdopen(fd), mode)
closes the file descriptor fd. If you want to keep fd open, use
gzdopen(dup(fd), mode).
gzdopen() returns
NULL
if there
was insufficient memory to allocate the (de)compression state.
-
-
- int
gzsetparams(gzFile file,
int level, int strategy);
-
The gzsetparams() function dynamically updates the
compression level or strategy. See the description of
deflateInit2() for the meaning of these parameters.
gzsetparams() returns
Z_OK
if
successful, or Z_STREAM_ERROR
if the file was not
opened for writing.
-
-
- int
gzread(gzFile file,
voidp buf, unsigned len);
-
The gzread() function reads the given number of
uncompressed bytes from the compressed file. If the input file was not in
gzip format, gzread() copies the given number of bytes
into the buffer.
gzread() returns the number of uncompressed bytes actually
read (0 for end of file, -1 for error).
-
-
- int
gzwrite(gzFile file,
const voidp buf, unsigned
len);
-
The gzwrite() function writes the given number of
uncompressed bytes into the compressed file. gzwrite()
returns the number of uncompressed bytes actually written (0 in case of
error).
-
-
- int
gzprintf(gzFile file,
const char *format, ...);
-
The gzprintf() function converts, formats, and writes the
args to the compressed file under control of the format string, as in
fprintf(3).
gzprintf() returns the number of uncompressed bytes
actually written (0 in case of error).
-
-
- int
gzputs(gzFile file,
const char *s);
-
The gzputs() function writes the given null-terminated
string to the compressed file, excluding the terminating null character.
gzputs() returns the number of characters written, or -1
in case of error.
-
-
- char *
gzgets(gzFile file,
char *buf, int len);
-
The gzgets() function reads bytes from the compressed file
until len-1 characters are read, or a newline character is read and
transferred to buf, or an end-of-file condition is
encountered. The string is then terminated with a null character.
gzgets() returns buf, or
Z_NULL
in case of error.
-
-
- int
gzputc(gzFile file,
int c);
-
The gzputc() function writes c,
converted to an unsigned char, into the compressed file.
gzputc() returns the value that was written, or -1 in
case of error.
-
-
- int
gzgetc(gzFile file);
-
The gzgetc() function reads one byte from the compressed
file. gzgetc() returns this byte or -1 in case of end of
file or error.
-
-
- int
gzflush(gzFile file,
int flush);
-
The gzflush() function flushes all pending output into the
compressed file. The parameter flush is as in the
deflate() function. The return value is the
zlib error number (see function
gzerror() below). gzflush() returns
Z_OK
if the flush parameter is
Z_FINISH
and all output could be flushed.
gzflush() should be called only when strictly necessary
because it can degrade compression.
-
-
- z_off_t
gzseek(gzFile file,
z_off_t offset, int
whence);
-
Sets the starting position for the next gzread() or
gzwrite() on the given compressed file. The offset
represents a number of bytes in the uncompressed data stream. The whence
parameter is defined as in
lseek(2); the value
SEEK_END
is not supported.
If the file is opened for reading, this function is emulated but can be
extremely slow. If the file is opened for writing, only forward seeks are
supported; gzseek() then compresses a sequence of zeroes
up to the new starting position.
gzseek() returns the resulting offset location as measured
in bytes from the beginning of the uncompressed stream, or -1 in case of
error, in particular if the file is opened for writing and the new
starting position would be before the current position.
-
-
- int
gzrewind(gzFile file);
-
The gzrewind() function rewinds the given
file. This function is supported only for reading.
gzrewind(file) is equivalent to (int)gzseek(file, 0L, SEEK_SET).
-
-
- z_off_t
gztell(gzFile file);
-
The gztell() function returns the starting position for
the next gzread() or gzwrite() on the
given compressed file. This position represents a number of bytes in the
uncompressed data stream.
gztell(file) is equivalent to gzseek(file, 0L, SEEK_CUR).
-
-
- int
gzeof(gzFile file);
-
The gzeof() function returns 1 when
EOF
has previously been detected reading the given
input stream, otherwise zero.
-
-
- int
gzclose(gzFile file);
-
The gzclose() function flushes all pending output if
necessary, closes the compressed file and deallocates all the
(de)compression state. The return value is the zlib
error number (see function gzerror() below).
-
-
- const char
* gzerror(gzFile file,
int *errnum);
-
The gzerror() function returns the error message for the
last error which occurred on the given compressed
file. errnum is set to the
zlib error number. If an error occurred in the file
system and not in the compression library, errnum is
set to
Z_ERRNO
and the application may consult
errno to get the exact error code.
CHECKSUM FUNCTIONS
These functions are not related to compression but are exported anyway because
they might be useful in applications using the compression library.
-
-
- uLong
adler32(uLong adler,
const Bytef *buf, uInt
len);
- The adler32() function updates a running
Adler-32 checksum with the bytes buf[0..len-1] and returns the updated
checksum. If buf is
NULL
,
this function returns the required initial value for the checksum.
An Adler-32 checksum is almost as reliable as a CRC32 but can be computed
much faster. Usage example:
uLong adler = adler32(0L, Z_NULL, 0);
while (read_buffer(buffer, length) != EOF) {
adler = adler32(adler, buffer, length);
}
if (adler != original_adler) error();
-
-
- uLong
crc32(uLong crc,
const Bytef *buf, uInt
len);
- The crc32() function updates a running
CRC with the bytes buf[0..len-1] and returns the updated CRC. If
buf is
NULL
, this function
returns the required initial value for the CRC. Pre- and post-conditioning
(one's complement) is performed within this function so it shouldn't be
done by the application. Usage example:
uLong crc = crc32(0L, Z_NULL, 0);
while (read_buffer(buffer, length) != EOF) {
crc = crc32(crc, buffer, length);
}
if (crc != original_crc) error();
STRUCTURES
struct internal_state;
typedef struct z_stream_s {
Bytef *next_in; /* next input byte */
uInt avail_in; /* number of bytes available at next_in */
uLong total_in; /* total nb of input bytes read so far */
Bytef *next_out; /* next output byte should be put there */
uInt avail_out; /* remaining free space at next_out */
uLong total_out; /* total nb of bytes output so far */
char *msg; /* last error message, NULL if no error */
struct internal_state FAR *state; /* not visible by applications */
alloc_func zalloc; /* used to allocate the internal state */
free_func zfree; /* used to free the internal state */
voidpf opaque; /* private data object passed to zalloc and zfree*/
int data_type; /*best guess about the data type: ascii or binary*/
uLong adler; /* Adler-32 value of the uncompressed data */
uLong reserved; /* reserved for future use */
} z_stream;
typedef z_stream FAR * z_streamp;
The application must update
next_in and
avail_in when
avail_in has dropped
to zero. It must update
next_out and
avail_out when
avail_out has
dropped to zero. The application must initialize
zalloc,
zfree, and
opaque before calling
the init function. All other fields are set by the compression library and
must not be updated by the application.
The
opaque value provided by the application will be
passed as the first parameter for calls to
zalloc() and
zfree(). This can be useful for custom memory management.
The compression library attaches no meaning to the
opaque value.
zalloc must return
Z_NULL
if there
is not enough memory for the object. If
zlib is used in a
multi-threaded application,
zalloc and
zfree must be thread safe.
On 16-bit systems, the functions
zalloc and
zfree must be able to allocate exactly 65536 bytes, but
will not be required to allocate more than this if the symbol MAXSEG_64K is
defined (see
<zconf.h>).
WARNING: On MSDOS, pointers returned by
zalloc for objects
of exactly 65536 bytes *must* have their offset normalized to zero. The
default allocation function provided by this library ensures this (see
zutil.c). To reduce memory requirements and avoid any
allocation of 64K objects, at the expense of compression ratio, compile the
library with -DMAX_WBITS=14 (see
<zconf.h>).
The fields
total_in and
total_out
can be used for statistics or progress reports. After compression,
total_in holds the total size of the uncompressed data
and may be saved for use in the decompressor (particularly if the decompressor
wants to decompress everything in a single step).
CONSTANTS
#define Z_NO_FLUSH 0
#define Z_PARTIAL_FLUSH 1 /* will be removed, use Z_SYNC_FLUSH instead */
#define Z_SYNC_FLUSH 2
#define Z_FULL_FLUSH 3
#define Z_FINISH 4
/* Allowed flush values; see deflate() below for details */
#define Z_OK 0
#define Z_STREAM_END 1
#define Z_NEED_DICT 2
#define Z_ERRNO (-1)
#define Z_STREAM_ERROR (-2)
#define Z_DATA_ERROR (-3)
#define Z_MEM_ERROR (-4)
#define Z_BUF_ERROR (-5)
#define Z_VERSION_ERROR (-6)
/* Return codes for the compression/decompression functions.
* Negative values are errors,
* positive values are used for special but normal events.
*/
#define Z_NO_COMPRESSION 0
#define Z_BEST_SPEED 1
#define Z_BEST_COMPRESSION 9
#define Z_DEFAULT_COMPRESSION (-1)
/* compression levels */
#define Z_FILTERED 1
#define Z_HUFFMAN_ONLY 2
#define Z_DEFAULT_STRATEGY 0
/* compression strategy; see deflateInit2() below for details */
#define Z_BINARY 0
#define Z_ASCII 1
#define Z_UNKNOWN 2
/* Possible values of the data_type field */
#define Z_DEFLATED 8
/* The deflate compression method
* (the only one supported in this version)
*/
#define Z_NULL 0 /* for initializing zalloc, zfree, opaque */
#define zlib_version zlibVersion()
/* for compatibility with versions < 1.0.2 */
VARIOUS HACKS
deflateInit and inflateInit are macros to allow checking the
zlib version and the compiler's view of
z_stream.
-
-
- int
deflateInit_(z_stream strm,
int level, const char *version,
int stream_size);
-
- int
inflateInit_(z_stream strm,
const char *version, int
stream_size);
-
- int
deflateInit2_(z_stream strm,
int level, int method,
int windowBits, int memLevel,
int strategy, const char
*version, int stream_size);
-
- int
inflateInit2_(z_stream strm,
int windowBits, const char
*version, int stream_size);
-
- const char
* zError(int err);
-
- int
inflateSyncPoint(z_streamp z);
-
- const uLongf
* get_crc_table(void);
-
SEE ALSO
- RFC 1950
- ZLIB Compressed Data Format Specification.
- RFC 1951
- DEFLATE Compressed Data Format Specification.
- RFC 1952
- GZIP File Format Specification.
zlib
HISTORY
This manual page is based on an HTML version of
<zlib.h> converted by
piaip
<
piaip@csie.ntu.edu.tw>
and was converted to mdoc format by the
OpenBSD
project.
AUTHORS
Jean-loup Gailly
<
jloup@gzip.org>
Mark Adler
<
madler@alumni.caltech.edu>