Microsoft KB Archive/135326

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PRB: _lseek Fails on Different Offset Values

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Q135326

--- The information in this article applies to: - The C Run-time (CRT) included with: - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52 --- SYMPTOMS ======== The Run-Time function _lseek fails on different offset values (number of bytes from origin). For example, in the following sample code, _lseek fails if it seeks to the offset positions 0x1ffff, 0x2ffff, 0x3ffff and so on in a file. CAUSE ===== This behavior occurs when you fail to include the required header file IO.H. This header file contains the prototype for the _lseek function. RESOLUTION ========== Include the header file. STATUS ====== This behavior is by design. MORE INFORMATION ================ If the code is compiled with warning level 3 or higher, the compiler will indicate that the function is not defined. It is a good idea to compile all code with a high warning level to prevent problems like this from happening. Sample Code to Reproduce Behavior - /* Compile options needed: None */ #include #include #include #include #include // #include // Uncomment this line to fix the problem void main { int File; long temp; if ((File = _open("test.dat", O_RDWR | O_BINARY, S_IWRITE)) == -1 ){ printf("File open error \n"); exit(1); } temp = 0x0001fffeL; // This read works if (_lseek(File, temp, SEEK_SET) == -1L) printf("Error reading from position: %lx\n", temp); else printf("Read OK from position: %lx\n",temp); temp = 0x0001ffffL; // This read fails if (_lseek(File, temp, SEEK_SET) == -1L) printf("Error reading from position: %lx\n", temp); else printf("Read OK from position: %lx\n",temp); _close(File); } Additional query words: 8.00 8.00c lseek

Keywords : kb16bitonly kbLangC kbVC

Issue type : kbprb

Technology : kbVCsearch kbAudDeveloper kbCRT