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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);
}
}
}
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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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