最近为了安全，在数据访问类上加了一个安全插入和安全更新方法。数据在插入前先过滤危险字串，并对数据类型，长度进行检查。 问题出来了，在长度检查方面，数据库使用的是varchar，长度是按字符个数算的，比如abcdef算6个字符，一二三四五六也算六个字符。而
最近为了安全，在数据访问类上加了一个安全插入和安全更新方法。数据在插入前先过滤危险字串，并对数据类型，长度进行检查。
问题出来了，在长度检查方面，数据库使用的是varchar，长度是按字符个数算的，比如“abcdef”算6个字符，“一二三四五六”也算六个字符。而php的strlen方法算出并不一样，strlen("abcdef")是6，而strlen("一二三四五六")是18。这样检查起来就麻烦了。
网上查找了php中文字符数，说用mb_strlen。
查了一下手册：
int mb_strlen ( string str [, string encoding] )
mb_strlen() returns number of characters in string str having character encoding encoding. A multi-byte character is counted as 1.
encoding is character encoding for str. If encoding is omitted, internal character encoding is used.
原来这个函数，是针对字数的，根据不同编码。对于某些字符，多字节的也计算为1，就它了。
试了一下，mb_strlen('abcdef','utf-8')和mb_strlen('一二三四五六','utf-8')都等于6。行了~
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