(mysql.info.gz) mysql_num_fields
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22.2.3.41 `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 3.22.24 or newer. To pass a
`MYSQL*' argument, you must use `unsigned int mysql_field_count(MYSQL
*mysql)' instead.
Description
...........
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.
`NULL mysql_store_result()' NULL mysql_store_result.
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_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)' is = 0. This will happen only if
something went wrong.
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