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mysql_num_fields()
unsigned int mysql_num_fields(MYSQL_RES *result)
or:
unsigned int mysql_num_fields(MYSQL *mysql)
The second form doesn't work on MySQL Version 3.22.24 or newer. To pass a
MYSQL*
argument, you must use
unsigned int mysql_field_count(MYSQL *mysql)
instead.
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 or
not the query was a SELECT
(or SELECT
-like) statement. The
example shown here illustrates how this may be done.
See section NULL mysql_store_result()
.
An unsigned integer representing the number of fields in a result set.
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 if
mysql_field_count(&mysql)
is = 0. This will happen only if something
went wrong.
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