MySQL C API: check if a field exists -

i'm new mysql programming on c. need check if user exists in table. how can using c api? here's i've got, isn't working:

if (mysql_query(con, "select * users username='user3'"))    {       finish_with_error(con);   }         mysql_res *result = mysql_store_result(con);   if (result == null)    {       finish_with_error(con);   }   int count = mysql_field_count(con);   printf("%d\n", count ); 

for interested, wrote using comments, , ended using.

if (mysql_query(con, "select field table username='user1'"))  {     finish_with_error(con); }  mysql_res *result = mysql_store_result(con);  if (result == null)  {     finish_with_error(con); }    mysql_row row; mysql_field *field;  if (row = mysql_fetch_row(result)) {     printf("%s\n", row[0]);     db_pwd = row[0]; }