25.2.3.20. mysql_fetch_lengths()
unsigned long *mysql_fetch_lengths(MYSQL_RES
*result)
Description
Returns the lengths of the columns of the current row within a
result set. If you plan to copy field values, this length
information is also useful for optimization, because you can
avoid calling strlen(). In addition, if the
result set contains binary data, you
must use this function to
determine the size of the data, because
strlen() returns incorrect results for any
field containing null characters.
The length for empty columns and for columns containing
NULL values is zero. To see how to
distinguish these two cases, see the description for
mysql_fetch_row().
Return Values
An array of unsigned long integers representing the size of
each column (not including any terminating null characters).
NULL if an error occurred.
Errors
mysql_fetch_lengths() is valid only for the
current row of the result set. It returns
NULL if you call it before calling
mysql_fetch_row() or after retrieving all
rows in the result.
Example
MYSQL_ROW row;
unsigned long *lengths;
unsigned int num_fields;
unsigned int i;
row = mysql_fetch_row(result);
if (row)
{
num_fields = mysql_num_fields(result);
lengths = mysql_fetch_lengths(result);
for(i = 0; i < num_fields; i++)
{
printf("Column %u is %lu bytes in length.\n", i, lengths[i]);
}
}
