Q131060 - PRB: Wrong Result from Expression with Mixed Types & Sizeof

PRB: Wrong Result from Expression with Mixed Types & Sizeof

Q131060

1.50 1.51 1.52 WINDOWS kbtool kbprb --------------------------------------------------------------------- The information in this article applies to: The Microsoft C/C++ Compiler (CL.EXE), included with: - Microsoft Visual C++ for Windows, versions 1.5, 1.51, and 1.52 --------------------------------------------------------------------- SYMPTOMS ======== Expressions that use the sizeof operator and values of more than one type can generate the wrong result. RESOLUTION ========== Avoid mixed-mode expressions containing the sizeof operator. STATUS ====== This behavior is by design. It is in compliance with the rules of ANSI C. The result type of the sizeof operator is size_t, which is defined in STDDEF.H to be unsigned int. Promoting the int to unsigned int causes the problem. MORE INFORMATION ================ When compiled with one of the products listed above, the following sample code displays this result: Failed: x = 65532 The expected result is this: x = -4 Sample Code to Demonstrate Behavior ----------------------------------- /* Compile options needed: none */ #include <stdio.h> void main(void) { long x; //Work-around: comment this line and uncomment the next line x = -1*sizeof(long); //x = -1*(int)sizeof(long); if (x != -4) printf("Failed: "); printf("x = %ld\n",x); } Additional reference words: 1.50 8.00c calculation no32bit KBCategory: kbtool kbprb KBSubcategory: CPPiss

Keywords : kb16bitonly kbCompiler kbCPPonly kbVC
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Technology : kbVCsearch kbAudDeveloper kbCVCComp