Article ID: 50712
Article Last Modified on 12/12/2003
APPLIES TO
- The C Run-Time (CRT), when used with:
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 1.5 Professional Edition
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 2.0 Professional Edition
- Microsoft Visual C++ 2.1
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 5.0 Standard Edition
- Microsoft Visual C++ 6.0 Service Pack 5
This article was previously published under Q50712
SUMMARY
The C run-time routines assume that the direction flag is cleared. If you are using other functions with the C run-time functions, you must ensure that the other functions leave the direction flag alone or restore it to its original condition. Expecting the direction flag to be clear upon entry makes the run-time code faster and more efficient. The direction flag is a CPU flag specific to Intel 80x86 processors. It applies to all assembly instructions that use the REP (repeat) prefix, such as MOVS, MOVSD, MOVSW, etc. Addresses provided to applicable instructions are increased if the direction flag is cleared.
The CRT function, such as the string manipulation and buffer manipulation routines, expect the direction flag to be clear. This is usually the case and is documented in the "Microsoft Macro Assembler Programmer's Guide," for versions 5.0 and 5.1, as follows:
Under DOS, the direction flag will normally be cleared if your program has not changed it.
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Keywords: kbdocerr KB50712