unsigned long mysql_real_escape_string(MYSQL *mysql, char *to, const char *from, unsigned long length)

This function creates a legal SQL string for use in an SQL statement. SeeString Literals.

Themysqlargument must be a valid, open connection because character escaping depends on the character set in use by the server.

The string in thefromargument is encoded to produce an escaped SQL string, taking into account the current character set of the connection. The result is placed in thetoargument, followed by a terminating null byte.

Characters encoded are\,',",NUL(ASCII 0),\n,\r, and Control+Z. Strictly speaking, MySQL requires only that backslash and the quote character used to quote the string in the query be escaped.mysql_real_escape_string()quotes the other characters to make them easier to read in log files. For comparison, see the quoting rules for literal strings and theQUOTE()SQL function inString Literals, andString Functions and Operators.

The string pointed to byfrommust belengthbytes long. You must allocate thetobuffer to be at leastlength*2+1bytes long. (In the worst case, each character may need to be encoded as using two bytes, and there must be room for the terminating null byte.) Whenmysql_real_escape_string()returns, the contents oftois a null-terminated string. The return value is the length of the encoded string, not including the terminating null byte.

If you must change the character set of the connection, use themysql_set_character_set()function rather than executing aSET NAMES(orSET CHARACTER SET) statement.mysql_set_character_set()works likeSET NAMESbut also affects the character set used bymysql_real_escape_string(), whichSET NAMESdoes not.

The following example inserts two escaped strings into anINSERTstatement, each within single quote characters:

char query[1000],*end; end = my_stpcpy(query,"INSERT INTO test_table VALUES('"); end += mysql_real_escape_string(&mysql,end,"What is this",12); end = my_stpcpy(end,"','"); end += mysql_real_escape_string(&mysql,end,"binary data: \0\r\n",16); end = my_stpcpy(end,"')"); if (mysql_real_query(&mysql,query,(unsigned int) (end - query))) { fprintf(stderr, "Failed to insert row, Error: %s\n", mysql_error(&mysql)); }

Themy_stpcpy()function used in the example is included in thelibmysqlclientlibrary and works likestrcpy()but returns a pointer to the terminating null of the first parameter.

The length of the encoded string that is placed into thetoargument, not including the terminating null byte, or -1 if an error occurs.

Becausemysql_real_escape_string()returns an unsigned value, you can check for -1 by comparing the return value to(unsigned long)-1(or to(unsigned long)~0, which is equivalent).