提供一些项目中常用的字符串操作功能包括：截取字符串长度、输出转换、随机字符串、全角半角转换、字符集转换、邮箱格式验证、数字转文件大小.
随机字符串,:
/**
* 随机字符串
* @param number $leng
* @param string $type
* @return string
*/
public static function RandomCode($leng=12,$type="all"){
$leng=$leng>0?intval($leng):12;
$str="";
if($type=='num'){
for($i=0;$i<$leng;$i++){
mt_srand(doubleval（microtime()*1000000));
$str.=chr(mt_rand(48,57));
}
}elseif($type=='capital'){
for($i=0;$i<$leng;$i++){
mt_srand(doubleval（microtime()*1000000));
$str.=chr(mt_rand(65,90));
}
}elseif($type=='lower'){
for($i=0;$i<$leng;$i++){
mt_srand(doubleval（microtime()*1000000));
$str.=chr(mt_rand(97,122));
}
}else{
$char=array("1","2","3","4","5","6","7","8","9","0","a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z","A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z");
shuffle($char);
$n=count($char)-1;
$str="";
for($i=0;$i<$leng;$i++){
mt_srand(doubleval（microtime()*1000000));
$m=mt_rand(0,$n);
$str.=$char[$m];
}
}
return $str;
}
全角转换为半角:
/** semiangle 全角转换为半角
*
* @param string $str
* @return string 返回全角转换为半角后的字符串 */
public static function Semiangle($str){
$arr=array('０'=>'0','１'=>'1','２'=>'2','３'=>'3','４'=>'4','５'=>'5','６'=>'6','７'=>'7','８'=>'8','９'=>'9','（'=>'(','）'=>')','［'=>'[','］'=>']','【'=>'[','】'=>']','〖'=>'[','〗'=>']','「'=>'[','」'=>']','『'=>'[','』'=>']','｛'=>'{','｝'=>'}','《'=>'<','》'=>'>','％'=>'%','＋'=>'+','—'=>'-','－'=>'-','～'=>'-','：'=>':','。'=>'.','、'=>',','，'=>'.','、'=>'.','；'=>',','？'=>'?','！'=>'!','…'=>'-','‖'=>'|','＂'=>'"','＇'=>'\'','｀'=>'\'','｜'=>'|','〃'=>'"',' '=>' ');
return strtr($str,$arr);
}
主要代码功能: 随机字符串, 全角转换为半角.
doubleval（) floatval()的别名, 获取变量的浮点值.
chr() 返回相对于Ascii码所指定的字符.此函数与 ord() 是互补的。
mt_rand() 使用 Mersenne Twister 算法返回随机整数。例如想要 5 到 15（包括 5 和 15）之间的随机数，用 mt_rand(5, 15)。
代码段持续更新中...如果没有你需要的,可以留下你的评论,告诉你的需求.
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