Q38189: SDK C Documentation Incorrect for memcpy

Article: Q38189
Product(s): See article
Version(s): 4.50   | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | docerr | mspl13_c
Last Modified: 18-NOV-1988

Page 339 of the "Microsoft Operating System/2 Software Development
Kit/ Microsoft C Optimizing Compiler Run-Time Library Reference"
incorrectly states that the memcpy function ensures proper copying of
source bytes to the destination if both regions overlap. Microsoft C
Optimizing Compiler Versions 4.50 or later do not guarantee that
source bytes in the overlapping area are copied before being
overwritten.

The memcpy function in Version 4.00 of the Microsoft C compiler
ensures that copying worked for overlapping regions. Starting with the
Microsoft C Compiler Version 4.50, this was no longer true. The OS/2
SDK was first released with C Version 4.50 without the new Microsoft C
run-time library reference documentation. When the OS/2 SDK package
was updated to C Versions 5.00 and 5.10, the old Microsoft C run-time
library reference was not updated. The separate retail packages of the
Microsoft C Optimizing Compiler Versions 5.00 and 5.10 has the new C
run-time library reference.

The change was made because ANSI requires that the memmove function,
not the memcpy function, be used to copy overlapping regions. Because
no memmove function exists in the Microsoft C Compiler Version 4.00,
and Microsoft follows ANSI standards, the function memcpy included
overlapping checking. The added memmove function in C Version 5.00
prompted the change in the memcpy function. The memmove was added to
handle overlapping regions while memcpy (the old handler of overlapped
regions) was implemented as the "fast" copy.

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