PRB: Compiler Lacks Warnings for Options Incompatible with /u

• The Microsoft 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, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52 - Microsoft Visual C++ 32-bit Edition, version 1.0, 2.0, 2.1, 4.0, 5.0

SYMPTOMS

In the Microsoft C/C++ compiler, the /u compiler option turns off the definition of all predefined identifiers. Therefore, other compiler options that implicitly define identifiers are incompatible with /u. Nevertheless, no warnings or errors are generated if an option incompatible with /u is specified.

For example, the /J option changes the default char type from signed char to unsigned char and implicitly defines the macro _CHAR_UNSIGNED. If both /u and /J are specified on the same command line, the default char type for that translation unit will be unsigned char but _CHAR_UNSIGNED will not be defined. Moreover, the compiler issues no warning, not even at warning level 4, that /u will undefine those macros defined by /J.

CAUSE

This is expected behavior. The /U (undefine) option turns off the definition of an single identifier already defined for the preprocessor. The /u option turns off every defined identifier. Both the /U and /u options apply to predefined names and user defined ones.