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Top Forums Programming Atomic Read and Write with stdio Post 302452913 by Corona688 on Monday 13th of September 2010 11:18:48 AM
Old 09-13-2010
File I/O is not atomic.
 

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FREAD(3)						   BSD Library Functions Manual 						  FREAD(3)

NAME
fread, fwrite -- binary stream input/output LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <stdio.h> size_t fread(void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream); size_t fwrite(const void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream); DESCRIPTION
The function fread() reads nitems objects, each size bytes long, from the stream pointed to by stream, storing them at the location given by ptr. The function fwrite() writes nitems objects, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr. RETURN VALUES
The functions fread() and fwrite() advance the file position indicator for the stream by the number of bytes read or written. They return the number of objects read or written. If an error occurs, or the end-of-file is reached, the return value is a short object count (or zero). The function fread() does not distinguish between end-of-file and error; callers must use feof(3) and ferror(3) to determine which occurred. The function fwrite() returns a value less than nitems only if a write error has occurred. SEE ALSO
read(2), write(2) STANDARDS
The functions fread() and fwrite() conform to ISO/IEC 9899:1990 (``ISO C90''). BSD
March 8, 1994 BSD
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