Checking if value is not in the table ..help..please (Mysql + C)

My purpose is to warn the user whenever he/she insert a value which is not in the table.

Table :

For_Sconti  |    Cat_Sconti    |  Sconto 

  7148               开发者_StackOverflowA1          451.00

Someone cleverly suggested to use mysql_affected_rows() function.

Since it can be used when an update statement is issued, I tried to understand how it works but to no avail.

Here's the code I use:

memset(query, 0, 200);
            strcat(query, "UPDATE Sconti SET ");
            strcat(query, "Sconto = '");
            strcat(query, nuovo_sconto);
            strcat(query, "' WHERE For_Sconti ='");
            strcat(query, For_Sconti);
            strcat(query, "' AND Cat_Sconti='");
            strcat(query, Cat_Sconti);
            strcat(query, "';");
            if ( (mysql_affected_rows()) == 0 )
            printf("Warning you tried to modify non existent record\n" );

This is the error message I get:

2.0.c: In function ‘modifica_sconto’:
2.0.c:330: error: too few arguments to function ‘mysql_affected_rows’

Can someone help get out of trouble?

Any help will be highly appreciated.

---

1. You have generated the update statement, but you are not executing it. You need to execute your update statement using mysql_query()

2. You need to pass your mysql connection handle structure (MYSQL *) as a parameter to mysql_affected_rows()

   char *stmt = "UPDATE products SET cost=cost*1.25 WHERE group=10"; mysql_query(&mysql,stmt); printf("%ld products updated", (long) mysql_affected_rows(&mysql));

References :

1. http://dev.mysql.com/doc/refman/5.0/en/mysql-affected-rows.html