Advantages and disadvantages of mysqli_set_charset and SETNAMES in php

Advantages and disadvantages of mysqli_set_charset and SETNAMES in php

// 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 )){ // ** Call the corresponding libmysql function RETURN_FALSE; } RETURN_TRUE; } ?> What does mysql_set_character_set do? // Mysql-5.1.30-SRC/libmysql/client. c, line 3166: Int STDCALLmysql_set_character_set (MYSQL * mysql, const char * cs_name) { Structcharset_info_st * cs; Const char * save_csdir = charsets_dir; If (mysql-> options. charset_dir) Charsets_dir = mysql-> options. charset_dir; If (strlen (cs_name) <MY_CS_NAME_SIZE && (Cs = get_charset_by_csname (cs_name, MY_CS_PRIMARY, MYF (0 )))) { Char buff [MY_CS_NAME_SIZE + 10]; Charsets_dir = save_csdir; /* Skip execution of "set names" for pre-4.1 servers */ If (mysql_get_server_version (mysql) <40100) Return 0; Sprintf (buff, "set names % s", cs_name ); If (! Mysql_real_query (mysql, buff, strlen (buff ))) { Mysql-> charset = cs; } } // The following content is omitted ?> We can see that in addition to "set names", mysqli_set_charset has done one more step: Sprintf (buff, "set names % s", cs_name ); If (! Mysql_real_query (mysql, buff, strlen (buff ))) { Mysql-> charset = cs; } ?> What is the role of charset, a member of the mysql core structure? This tells us about mysql_real_escape_string (). The difference between this function and mysql_escape_string is that it considers the "current" character set. Where can this current character set come from? By the way, you guessed it was mysql-> charset. Mysql_real_string in the determination of wide character set characters, according to the member variables to adopt different policies, for example, if it is UTF-8, then libmysql/ctype-utf8.c will be used. Check the instance. the default mysql connection character set is latin-1 (classic 5c problem ): $ Db = mysql_connect ('localhost: 100', 'root', '123 '); Mysql_select_db ("test "); $ A = "\ x91 \ x5c"; // gbk encoding for "bytes". the low byte is 5c, that is, "\" in ascii "\" Var_dump (addslashes ($ )); 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 )); ?> Because the gbk encoding of "bytes" is low-byte 5c, that is, "\" in ascii, and because mysql (I) _ set_charset affects mysql-> charset, the default value is mysql> charset at other times. Therefore, the result is $ php-f 5c. phpstring (3) "inline \" string (3) "inline \" string (3) "inline \" string (2) "inline" This article