Possible Cause for Slow Stream I/O

ID: Q46741

5.10 6.00 6.00a 6.00ax 7.00 | 1.00 1.50

MS-DOS                      | WINDOWS
kbprg

The information in this article applies to:

In Microsoft C, the stream level I/O routines inherit their speed and flexibility from the buffering system they use. Upon opening a file with the fopen() function, a file record is created that contains pointers into a stream buffer. This buffer is then allocated (malloc-ed) when the first I/O operation is performed. If there is not enough room in the heap for this buffer allocation, the file operation continues with a buffer size of one character.

A stream I/O routine that takes an excessive amount of time is probably the result of a failure to allocate the 512-byte buffer on the heap (near or far, depending on the memory model). Without this buffer, the I/O routines are extremely slow, requiring disk access for all I/O operations.

Use one of the following two methods to work around this problem:

Additional reference words: kbinf 1.00 1.50 5.10 6.00 6.00a 6.00ax 7.00 KBCategory: kbprg KBSubcategory: CRTIss Keywords : kb16bitonly

Last Reviewed: July 18, 1997