(PHP 4 >= 4.0.1, PHP 5)
crc32 — 计算一个字符串的 crc32 多项式
$str
)
生成 str
的 32 位循环冗余校验码多项式。这通常用于检查传输的数据是否完整。
由于 PHP 的整数是带符号的，所以在 32 位系统上许多 crc32 校验码将返回负整数。 尽管在 64 位上所有 crc32() 的结果将都是正整数。
因此你需要使用 sprintf() 或 printf() 的“%u”格式符来获取表示无符号 crc32 校验码的字符串。
For a hexadecimal representation of the checksum you can either use the "%x" formatter of sprintf() or printf() or the dechex() conversion functions, both of these also take care of converting the crc32() result to an unsigned integer.
Having 64bit installations also return negative integers for higher result values was considered but would break the hexadecimal conversion as negatives would get an extra 0xFFFFFFFF######## offset then. As hexadecimal representation seems to be the most common use case we decided to not break this even if it breaks direct decimal comparisons in about 50% of the cases when moving from 32 to 64bits.
In retrospect having the function return an integer maybe wasn't the best idea and returning a hex string representation right away (as e.g. md5() does) might have been a better plan to begin with.
For a more portable solution you may also consider the generic
hash(). hash("crc32b", $str) will
return the same string as dechex(crc32($str)).
str
要校验的数据。
返回 str crc32 校验的整数。
Example #1 显示一个 crc32 校验码
示例中的第二行演示了如何使用 printf() 函数转换校验码：
<?php
$checksum = crc32("The quick brown fox jumped over the lazy dog.");
printf("%u\n", $checksum);
?>