MySQL :: MySQL 8.4 C API Developer Guide :: 5.4.60 mysql_real_escape_string() (original) (raw)

5.4.60 mysql_real_escape_string()

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

Description

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

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

The string in the from argument is encoded to produce an escaped SQL string, taking into account the current character set of the connection. The result is placed in the to argument, 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 the QUOTE() SQL function in String Literals, andString Functions and Operators.

The string pointed to by from must belength bytes long. You must allocate theto buffer to be at leastlength*2+1 bytes 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 of to is 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 the mysql_set_character_set() function rather than executing a SET NAMES (or SET CHARACTER SET) statement.mysql_set_character_set() works like SET NAMES but also affects the character set used bymysql_real_escape_string(), which SET NAMES does not.

Example

The following example inserts two escaped strings into anINSERT statement, 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));
}

The my_stpcpy() function used in the example is included in the libmysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.

Return Values

The length of the encoded string that is placed into theto argument, 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).

Errors