PRB: Constant String Is Eliminated by the C++ Compiler

• The Microsoft C/C++ Compiler (CL.EXE) included with: - 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, versions 1.0, 2.0, 2.1, 4.0, 4.1,

       4.2, 5.0
  

SYMPTOMS

The Microsoft C/C++ versions 7.0 and later compilers eliminate unreferenced constant strings. This happens only with C++ source, not C source. The string is declared in the source file, but is not included in the resulting object module.

CAUSE

In C++, const variables have internal linkage. This is different from the way that C handles const variables.

In this case, because the C++ compiler can process only one source file at a time, the string is eliminated if it is not referenced in the file in which it is declared, even if it is referenced from another file.

RESOLUTION

The solution is to declare the const string as "extern". This provides external linkage, telling the compiler that the string may be used in another module, and not to assume that it is an unreferenced symbol; for example

   const char sz[] = "\"the string\"";

   extern const char sz[] = "\"the string"\";

MORE INFORMATION

While this behavior is not a bug in the compiler, the effects of this optimization may cause unexpected results. If a string is declared and initialized in one module, and referenced only in another module, the string will be eliminated from the first module. This means that the other file will not have access to the information used in the initialization of the string.

For more information on internal and external linkage, see section 2.4 of the ""C++ Language Reference"" supplied with C/C++ version 7.0 and Visual C++, or refer to the online help supplied with Visual C++.