gzcompress()

(PHP 4 >= 4.0.1, PHP 5, PHP 7)

Compress a string

说明

This function compresses the given string using theZLIBdata format.

For details on the ZLIB compression algorithm see the document "» ZLIB Compressed Data Format Specification version 3.3"(RFC 1950).

This isnotthe same as gzip compression, which includes some header data. See gzencode() for gzip compression.

参数

The data to compress.

The level of compression. Can be given as 0 for no compression up to 9 for maximum compression.

If -1 is used, the default compression of the zlib library is used which is 6.

One of ZLIB_ENCODING_* constants.

返回值

The compressed string or FALSE if an error occurred.

范例

gzcompress() example

更新日志

参见

• gzdeflate()Deflate a string
• gzinflate()Inflate a deflated string
• gzuncompress()Uncompress a compressed string
• gzencode()Create a gzip compressed string

Did some simple benchmarking of gzcompress() this morning on a lightly-loaded Fedora 12 server with an AMD Phenom II 940 (quad-core) rocking 8 gigs of ram and executing PHP 5.3.2.2 as an Apache module:
Compression benchmark: (level, time, size (%)):
0: 0.000373 - 82.08 kB (100.02%)
1: 0.000914 - 19.61 kB (23.90%)
2: 0.000951 - 18.88 kB (23.01%)
3: 0.000999 - 18.43 kB (22.46%)
4: 0.001498 - 17.65 kB (21.51%)
5: 0.001744 - 17.09 kB (20.82%)
6: 0.002060 - 16.88 kB (20.57%)
7: 0.002233 - 16.85 kB (20.53%)
8: 0.002808 - 16.71 kB (20.36%)
9: 0.002928 - 16.71 kB (20.36%)
The time code evaluates to:
1. Get start microtime
2. Call gzcompress
3. Get end microtime
4. Report average duration of 100 cycles
The 82.08 kB was a copied and pasted string of two actual, PHP-generated pages we use on our intranet. Running some rough calculations, the time it takes to compress the data at level 9 will never be larger than the time it takes to transmit slightly-less compressed data at levels 6 or lower. In other words, in our application, we have no reason not to fully-compress each PHP script's output.

GZ-compression works perfectly for html content sent to IE5/IE5.5/Netscape6 browsers. I even compress the  javascript code. It speeds throughput immensely: best case so far 160k html file --> 8k gzip sent.
Netscape 4 (on all platforms[?]), IE4/IE5 on the Mac do NOT support gz-compression. Email me if you want to know more.

No, it doesn't return gzip compressed data -- specifically, the CRC is messed up. However, after massaging the output a lot, I have come up with a solution. I also commented it a lot, pointing out odd things.

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