(mysql.info) mysql-num-fields

 
 22.2.3.46 `mysql_num_fields()'
 ..............................
 
 `unsigned int mysql_num_fields(MYSQL_RES *result)'
 
 To pass a `MYSQL*' argument instead, use `unsigned int
 mysql_field_count(MYSQL *mysql)'.
 
 *Description*
 
 Returns the number of columns in a result set.
 
 Note that you can get the number of columns either from a pointer to a
 result set or to a connection handle. You would use the connection
 handle if `mysql_store_result()' or `mysql_use_result()' returned
 `NULL' (and thus you have no result set pointer). In this case, you can
 call `mysql_field_count()' to determine whether `mysql_store_result()'
 should have produced a non-empty result. This allows the client program
 to take proper action without knowing whether the query was a `SELECT'
 (or `SELECT'-like) statement. The example shown here illustrates how
 this may be done.
 
 See  null-mysql-store-result.
 
 *Return Values*
 
 An unsigned integer representing the number of columns in a result set.
 
 *Errors*
 
 None.
 
 *Example*
 
      MYSQL_RES *result;
      unsigned int num_fields;
      unsigned int num_rows;
 
      if (mysql_query(&mysql,query_string))
      {
          // error
      }
      else // query succeeded, process any data returned by it
      {
          result = mysql_store_result(&mysql);
          if (result)  // there are rows
          {
              num_fields = mysql_num_fields(result);
              // retrieve rows, then call mysql_free_result(result)
          }
          else  // mysql_store_result() returned nothing; should it have?
          {
              if (mysql_errno(&mysql))
              {
                 fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
              }
              else if (mysql_field_count(&mysql) == 0)
              {
                  // query does not return data
                  // (it was not a SELECT)
                  num_rows = mysql_affected_rows(&mysql);
              }
          }
      }
 
 An alternative (if you know that your query should have returned a
 result set) is to replace the `mysql_errno(&mysql)' call with a check
 whether `mysql_field_count(&mysql)' is = 0. This happens only if
 something went wrong.
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