PHP中数组的最大密钥大小是多少?-WhatisthemaxkeysizeforanarrayinPHP?

73  

It seems to be limited only by the script's memory limit.

它似乎只受脚本的内存限制。

A quick test got me a key of 128mb no problem:

一次快速的测试让我得到一把128mb的钥匙没有问题:

ini_set('memory_limit', '1024M');

$key = str_repeat('x', 1024 * 1024 * 128);

$foo = array($key => $key);

echo strlen(key($foo)) . "
";
echo strlen($foo[$key]) . "
";

14  

There is no practical limit to string size in PHP. According to the manual:

在PHP中，字符串大小没有实际的限制。根据手册:

Note: It is no problem for a string to become very large. PHP imposes no boundary on the size of a string; the only limit is the available memory of the computer on which PHP is running.

注意:字符串变得非常大是没有问题的。PHP对字符串的大小没有限制;唯一的限制是PHP所运行的计算机的可用内存。

It is safe to assume that this would apply to using strings as keys in arrays as well, but depending on how PHP handles its lookups, you may notice a performance hit as strings get larger.

可以假定这也适用于在数组中使用字符串作为键，但是根据PHP处理查找的方式，当字符串变大时，您可能会注意到性能受到的影响。

5  

In zend_hash.h, you can find zend_inline_hash_func() method that can show how to hash key string in PHP, So use key which string length less than 8 characters is better for performance.

在zend_hash。h，您可以找到zend_inline_hash_func()方法，它可以显示如何在PHP中对键字符串进行哈希，因此使用小于8个字符的字符串长度的键对性能更好。

static inline ulong zend_inline_hash_func(char *arKey, uint nKeyLength) {

register ulong hash = 5381;

/* variant with the hash unrolled eight times */
for (; nKeyLength >= 8; nKeyLength -= 8) {
    hash = ((hash <<5) + hash) + *arKey++;
    hash = ((hash <<5) + hash) + *arKey++;
    hash = ((hash <<5) + hash) + *arKey++;
    hash = ((hash <<5) + hash) + *arKey++;
    hash = ((hash <<5) + hash) + *arKey++;
    hash = ((hash <<5) + hash) + *arKey++;
    hash = ((hash <<5) + hash) + *arKey++;
    hash = ((hash <<5) + hash) + *arKey++;
}
switch (nKeyLength) {
    case 7: hash = ((hash <<5) + hash) + *arKey++; /* fallthrough... */
    case 6: hash = ((hash <<5) + hash) + *arKey++; /* fallthrough... */
    case 5: hash = ((hash <<5) + hash) + *arKey++; /* fallthrough... */
    case 4: hash = ((hash <<5) + hash) + *arKey++; /* fallthrough... */
    case 3: hash = ((hash <<5) + hash) + *arKey++; /* fallthrough... */
    case 2: hash = ((hash <<5) + hash) + *arKey++; /* fallthrough... */
    case 1: hash = ((hash <<5) + hash) + *arKey++; break;
    case 0: break;  EMPTY_SWITCH_DEFAULT_CASE()
}
    return hash;   
}