Microsoft KB Archive/115852

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PRB: sizeof Returns Nonzero Value for Zero-Sized Array

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Q115852

-- The information in this article applies to: - 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 and 1.5 - Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 4.0 -- SYMPTOMS ======== The sizeof operator will return a nonzero value when asked for the size of a zero-length array of any data type. A zero-sized array is legal only when the array is the last field in a struct or union. This syntax is specific to Microsoft, therefore, the /Ze compiler option (enable Microsoft Extentions) must be used. This behavior is by design. In C, sizeof must return the number of bytes necessary to tile the object in an array. Since each pointer must be unique, the size must be non-zero. MORE INFORMATION ================ The sample below can be used to illustrate this problem. If you use warning level 4 (/W4 option), the following warning message will be reported: warning C4200: nonstandard extension used : zero-sized array in struct/union Sample Code --- /* Compile options needed: none */ #include struct A { int a[0]; }; void main(void) { if( (int)(sizeof(struct A)) != 0 ) printf( "Failed\n" ); else printf( "Passed\n" ); } Additional query words: 7.00 8.00 8.00c 9.00 1.00 1.50 2.00

Keywords : kbCompiler

Issue type : kbprb

Technology : kbVCsearch kbAudDeveloper kbCVCComp