Q120153 - BUG: _read() Returns -1 When Reading Last Byte of a Segment

BUG: _read() Returns -1 When Reading Last Byte of a Segment

Q120153

1.00 1.50 WINDOWS kbprg kbbuglist ---------------------------------------------------------------------- The information in this article applies to: - The C Run-time (CRT) included with: - Microsoft C version 6.0, 6.0a, 6.0ax - Microsoft C/C++ version 7.0 - Microsoft Visual C++ for Windows, versions 1.0 and 1.5 ---------------------------------------------------------------------- SYMPTOMS ======== If you open a file with _open() specifying O_TEXT mode or letting it default to O_TEXT mode and then you call _read() to read to the last byte of a segment, the _read() function returns -1. Though this return value indicates that an error occurred, the information was read correctly. CAUSE ===== The carry flag is unexpectedly set when looking for carriage return, line feed (CR/LF) pairs at 0xFFFF. The Run-Time incorrectly interprets this as an error and returns -1 instead of the number of characters read. STATUS ====== Microsoft has confirmed this to be a bug in the products listed above. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available. MORE INFORMATION ================ The following sample code illustrates the problem: Sample Code ----------- /* Compile options needed: /AL */ #include <stdio.h> #include <fcntl.h> #include <sys\types.h> #include <sys\stat.h> #include <malloc.h> #include <io.h> #include <dos.h> #include <errno.h> int hfIn; int ret_val; char huge* lpcBase; char huge* lpcTest; void main(void) { lpcBase = (char _huge*) halloc(100000L, 1); lpcTest= lpcBase; FP_OFF(lpcTest)= 0xFFFC; // Point to end of the segment. hfIn = open("C:\\config.sys", _O_RDONLY); ret_val = read(hfIn, lpcTest, 4); if (ret_val< 0) { printf ("ret_val = %i indicating Failure Reading to 0xFFFF\n", ret_val); printf ("errno = %d\n", errno); } close(hfIn); } Additional reference words: 6.00 6.00a 6.00ax 7.00 7.00a 1.00 1.50 KBCategory: kbprg kbbuglist KBSubcategory: CRTIss

Keywords : kb16bitonly
Issue type :
Technology : kbVCsearch kbAudDeveloper kbCRT