How To Use malloc() and _fmalloc() in an Application (12159)
The information in this article applies to:
- The C Run-Time (CRT), when used with:
- Microsoft C for MS-DOS 5.1
- Microsoft C for MS-DOS 6.0
- Microsoft C for MS-DOS 6.0a
- Microsoft C for MS-DOS 6.0ax
- Microsoft C for OS/2 6.0a
- Microsoft C/C++ for MS-DOS 7.0
- Microsoft Visual C++ for Windows, 16-bit edition 1.0
- Microsoft Visual C++ for Windows, 16-bit edition 1.5
- Microsoft Visual C++, 32-bit Editions 1.0
- Microsoft Visual C++, 32-bit Editions 2.0
- Microsoft Visual C++, 32-bit Editions 4.0
This article was previously published under Q12159 SUMMARY
The text below provides information about using the _fmalloc() and
malloc() functions in an application.
An application can use both the malloc() and _fmalloc() functions
without restriction. Each function separately tracks its memory
allocations. The application must use the free() and _ffree()
functions, respectively, to free memory allocated by these functions.
The malloc() functions do not perform any "garbage collection"
activity to reclaim free memory between allocations. The application
must explicitly free memory when appropriate.
The malloc() functions can fragment memory. However, when an
application frees a block of memory that is adjacent to another block
of free memory, the appropriate free() function consolidates the
blocks to reduce the damage caused by fragmentation.
The _fmalloc() function does not allocate memory that crosses a
segment boundary and fails any allocation request for more than 64K of
memory. To allocate a larger memory block, use the halloc() function
(the huge memory model memory allocation function). Your application
must deal with segment boundaries in a huge memory block.
Windows NT uses a flat 32-bit memory model; every address requires 32
bits. Because Windows NT does not use segments, far and huge versions
of malloc() and free() are not required. Therefore, the C runtime
library that supports Windows NT does not include the _fmalloc(),
_ffree(), halloc(), and _hfree() functions. The elimination of
segments also removes the 64K maximum allocation limit; an application
can request up to 2 GB with malloc().
| Modification Type: | Minor | Last Reviewed: | 7/13/2004 |
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| Keywords: | kbCRT kbhowto KB12159 |
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