摘抄:mysql set names和set
首先介绍下 三个MySQL的”环境变量”设置命令及其作用: character_set_client: MySQL服务器, 客户端的编码集 character_set_connection: 传输给MySQL服务器的时候的编码集 character_set_results: 期望MySQL返回的结果的编码集 比如, 通过使用”SET NAME
首先介绍下三个MySQL的”环境变量”设置命令及其作用:
- character_set_client: MySQL服务器, 客户端的编码集
- character_set_connection:传输给MySQL服务器的时候的编码集
- character_set_results: 期望MySQL返回的结果的编码集
比如, 通过使用”SET NAMES utf8″, 就告诉服务器, 我用的是utf-8编码, 我希望你也给我返回utf-8编码的查询结果.
一般情况下, 使用”SET NAMES”就足够了, 也是可以保证正确的. 那么为什么手册又要说推荐使用mysqli_set_charset呢?
首先, 我们看看mysqli_set_charset到底做了什么(注意星号注释处, mysql_set_charset类似):
//php-5.2.11-SRC/ext/mysqli/mysqli_nonapi.c line 342 PHP_FUNCTION(mysqli_set_charset) { MY_MYSQL *mysql; zval *mysql_link; char *cs_name = NULL; unsigned int len; if (zend_parse_method_parameters(ZEND_NUM_ARGS() TSRMLS_CC, getThis() , "Os", &mysql_link, mysqli_link_class_entry, &cs_name, &len) == FAILURE) { return; } MYSQLI_FETCH_RESOURCE(mysql, MY_MYSQL*, &mysql_link, "mysqli_link" , MYSQLI_STATUS_VALID); if (mysql_set_character_set(mysql->mysql, cs_name)) { //** 调用libmysql的对应函数 RETURN_FALSE; } RETURN_TRUE; }
//mysql-5.1.30-SRC/libmysql/client.c, line 3166: int STDCALL mysql_set_character_set(MYSQL *mysql, const char *cs_name) { struct charset_info_st *cs; const char *save_csdir= charsets_dir; if (mysql->options.charset_dir) charsets_dir= mysql->options.charset_dir; if (strlen(cs_name) charset= cs; } } //以下省略
sprintf(buff, "SET NAMES %s", cs_name); if (!mysql_real_query(mysql, buff, strlen(buff))) { mysql->charset= cs; }
而对于mysql这个核心结构的成员charset又有什么作用呢?
这就要说说mysql_real_escape_string()了, 这个函数和mysql_escape_string的区别就是, 它会考虑”当前”字符集. 那么这个当前字符集从哪里来呢?
对了, 你猜的没错, 就是mysql->charset.
mysql_real_string在判断宽字符集的字符的时候, 就根据这个成员变量来分别采用不同的策略, 比如如果是utf-8, 那么就会采用libmysql/ctype-utf8.c.
看个实例, 默认mysql连接字符集是latin-1, (经典的5c问题):
<?php $db = mysql_connect('localhost:3737', 'root' ,'123456'); mysql_select_db("test"); $a = "\x91\x5c";//"慭"的gbk编码, 低字节为5c, 也就是ascii中的"\" var_dump(addslashes($a)); var_dump(mysql_real_escape_string($a, $db)); mysql_query("set names gbk"); var_dump(mysql_real_escape_string($a, $db)); mysql_set_charset("gbk"); var_dump(mysql_real_escape_string($a, $db)); ?>
所以, 结果就是:
$ php -f 5c.php string(3) "慭\" string(3) "慭\" string(3) "慭\" string(2) "慭"
个中细节有待进一步验证。原文适当修改。文章摘至:深入理解mysql SET NAMES和mysql(i)_set_charset

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