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28.7.7.48 mysql_num_fields()
unsigned int mysql_num_fields(MYSQL_RES
*result)
To pass a MYSQL*
argument instead, use
unsigned int mysql_field_count(MYSQL *mysql)
.
Description
Returns the number of columns in a result set.
You can get the number of columns either from a pointer to a
result set or to a connection handler. You would use the
connection handler 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 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_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 whether
mysql_field_count(&mysql)
returns 0. This happens only if something went wrong.
Document created the 26/06/2006, last modified the 26/10/2018
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