unsigned int mysql_field_count(MYSQL
*mysql)
If you are using a version of MySQL earlier than Version
3.22.24, you should use unsigned int
mysql_num_fields(MYSQL *mysql)
instead.
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.
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
.
Ésta es una traducción del manual de referencia de MySQL, que puede encontrarse en dev.mysql.com. El manual de referencia original de MySQL está escrito en inglés, y esta traducción no necesariamente está tan actualizada como la versión original. Para cualquier sugerencia sobre la traducción y para señalar errores de cualquier tipo, no dude en dirigirse a mysql-es@vespito.com.