27.7.6.22 mysql_field_count()
unsigned int mysql_field_count(MYSQL *mysql)
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 nonempty result. This enables 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.
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
.