Description:
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---
From manual page: http://www.php.net/function.str-replace#refsect1-function.str-replace-parameters
---
str_replace
count 
If passed, this will be set to the number of replacements performed. 
May be wrong
The role is to count.
this return a count, Not match the number of control.
Thanks!
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str_replace中的第四个参数count的作用的解释似乎是错误的。
它的作用是返回匹配的次数，而不是设置匹配的次数。
谢谢！

Test script:
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$str = 'THIS IS PHP,PHP IS VERY GOOD!I LIKE PHP VERYMUCH';
$search = 'PHP';
$replace = '<a href="http://www.php.net">PHP</a>';
$count=1;
echo str_replace($search, $replace, $str,$count) ;
echo ' >'.$count;