BUG: sizeof Used in Comparison Does Not Generate C4018

• The C/C++ Compiler (CL.EXE), included with:
  • Microsoft C for MS-DOS, versions 6.0, 6.0a, 6.0ax
  • Microsoft C/C++ for MS-DOS
  • Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5
  • Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0, 4.1, 4.2, 5.0, 6.0

SYMPTOMS

According to ANSI specifications, the sizeof macro returns the unsigned integer size of a particular data type or variable.

When the sizeof macro is used in a comparison with an integer variable, the compiler should, but does not, generate the following warning:

warning C4018: 'op' : signed/unsigned mismatch

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

The following sample code can be used to demonstrate the problem. The C4018 warning is produced for the statement in function3, but not for the statements in function1 and function2.

Sample Code

/* Compile options needed: /W4
*/ 

int i;
unsigned u;

int function1(void)
{
   return(i > sizeof(i));
}

int function2(void)
{
   return(i > (unsigned) sizeof(i));
}

int function3(void)
{
   u = sizeof(i);
   return(i > u);
} 

Additional query words: kbVC400bug 6.00 6.00a 6.00ax 7.00 8.00 8.00c 9.00

Keywords : kbCompiler kbVC100bug kbVC150bug kbVC200bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600bug
Version : winnt:1.0,2.0,4.0,4.1,4.2,5.0,6.0
Platform : winnt
Issue type : kbbug