(mysql.info) mysql-field-count

 
 22.2.3.22 `mysql_field_count()'
 ...............................
 
 `unsigned int mysql_field_count(MYSQL *mysql)'
 
 *Description*
 
 Returns the number of columns for the most recent query on the
 connection.
 
 The normal use of this function is when `mysql_store_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_field_count(&mysql) == 0)
              {
                  // query does not return data
                  // (it was not a SELECT)
                  num_rows = mysql_affected_rows(&mysql);
              }
              else // mysql_store_result() should have returned data
              {
                  fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
              }
          }
      }
 
 An alternative is to replace the `mysql_field_count(&mysql)' call with
 `mysql_errno(&mysql)'. In this case, you are checking directly for an
 error from `mysql_store_result()' rather than inferring from the value
 of `mysql_field_count()' whether the statement was a `SELECT'.
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