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

• The Microsoft C/C++ Compiler (CL.EXE)
  • Microsoft C/C++ for MS-DOS, version 7.0
  • Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52
  • Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 4.1, 4.2, 5.0, 6.0

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++.

Additional query words: 8.00 8.00c 9.00 9.10 L2029

Keywords : kbCompiler kbCPPonly kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC410 kbVC420 kbVC500 kbVC600
Version : MS-DOS:7.0;WINDOWS:1.0,1.5,1.51,1.52;WINDOWS NT:1.0,2.0,2.1,4.0,4.1,4.2,5.0
Platform : MS-DOS NT WINDOWS
Issue type : kbprb