实例
返回一个字符串，包含所有在 "hello world!" 中使用过的不同字符（模式 3）：
定义和用法
count_chars() 函数返回字符串所用字符的信息（例如，ASCII 字符在字符串中出现的次数，或者某个字符是否已经在字符串中使用过）。
语法
count_chars(string,mode)
参数 描述
string 必需。规定要检查的字符串。
mode 可选。规定返回模式。默认是 0。有以下不同的返回模式：
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0 - 数组，ASCII 值为键名，出现的次数为键值
1 - 数组，ASCII 值为键名，出现的次数为键值，只列出出现次数大于 0 的值
2 - 数组，ASCII 值为键名，出现的次数为键值，只列出出现次数等于 0 的值
3 - 字符串，带有所有使用过的不同的字符
4 - 字符串，带有所有未使用过的不同的字符
技术细节
返回值： 取决于指定的 mode 参数。
PHP 版本： 4+
更多实例
实例 1
返回一个字符串，包含所有在 "Hello World!" 中未使用过的字符（模式 4）：
实例 2
在本实例中，我们将使用 count_chars() 来检查字符串，返回模式设置为 1。模式 1 将返回一个数组，ASCII 值为键名，出现的次数为键值：
实例 3
统计 ASCII 字符在字符串中出现的次数另一个实例：
$value)
{
echo "The character '".chr($key)."' was found $value time(s)
";
}
?>count_chars实例
$val ) {
echo "There were $val instance(s) of \"" , chr ( $i ) , "\" in the string.
" ;
}
?>运行结果：
There were 4 instance(s) of " " in the string. There were 1 instance(s) of "." in the string. There were 1 instance(s) of "F" in the string. There were 2 instance(s) of "T" in the string. There were 1 instance(s) of "a" in the string. There were 1 instance(s) of "d" in the string. There were 1 instance(s) of "e" in the string. There were 2 instance(s) of "n" in the string. There were 2 instance(s) of "o" in the string. There were 1 instance(s) of "s" in the string. There were 1 instance(s) of "w" in the string.
