25.8.7.55 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 Section 10.1.1, “String Literals”.

Note

As of MySQL 5.7.6, mysql_real_escape_string() fails and produces an CR_INSECURE_API_ERR error if the NO_BACKSLASH_ESCAPES SQL mode is enabled. In this case, the function cannot escape quote characters except by doubling them, and to do this properly, it must know more information about the quoting context than is available. Instead, use mysql_real_escape_string_quote(), which takes an extra argument for specifying the quoting context.

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 Section 10.1.1, “String Literals”, and Section 13.5, “String Functions”.

The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*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.) When mysql_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 by mysql_real_escape_string(), which SET NAMES does not.

Example

The following example inserts two escaped strings into an INSERT 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 the to argument, not including the terminating null byte, or -1 if an error occurs.

Because mysql_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

• CR_INSECURE_API_ERR

  This error occurs as of MySQL 5.7.6 if the NO_BACKSLASH_ESCAPES SQL mode is enabled because, in that case, mysql_real_escape_string() cannot be guaranteed to produce a properly encoded result. To avoid this error, use mysql_real_escape_string_quote() instead.