Q50251: /Ol Causes Constant Overflow Warnings c4057 c4056

Article: Q50251
Product(s): See article
Version(s): 5.00 5.10 | 5.10
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 17-JUL-1990

The following small program, when compiled with loop optimization
(/Ol), produces the following warnings on the auto-decrement statement
in the second for loop:

   warning C4057: overflow in constant multiplication
   warning C4056: overflow in constant arithmetic

The warnings occur as a side effect of the optimization of the second
loop. Because the second loop has no functional value, it is optimized
to the loop-terminating conditions by the compiler. The warnings
appear to be benign; the program runs as expected. It is recommended,
however, that if you encounter these errors you generate an assembly
listing of the code and check the loop for correctness. These warnings
do not occur in any version of QuickC, QCL, or QuickAssembler.

Sample Code
-----------

#include<stdio.h>

void main(void)
{
     unsigned char *p1,
                      *start,
                      i,
                      j;

     start = "abcdefgh";
     for(i = 0, p1 = &start[7]; i < 7; i++){
          p1--;
          j = *p1;
     }
     for(i = 0, p1 = &start[7]; i < 7; i++){
          p1--;
     }
}

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