FREAD(3S)FREAD(3S)NAME
fread, fwrite - binary input/output
SYNOPSIS
#include <stdio.h>
size_t fread (void *ptr, size_t size, size_t nitems, FILE *stream);
size_t fwrite (const void *ptr, size_t size, size_t nitems, FILE
*stream);
DESCRIPTION
fread copies, into an array pointed to by ptr, up to nitems items of data
from the named input stream, where an item of data is a sequence of bytes
(not necessarily terminated by a null byte) of length size. fread stops
reading bytes if an end-of-file or error condition is encountered while
reading stream, or if nitems items have been read. The file pointer
associated with stream is positioned following the last byte read, which
may be at end-of-file. fread does not change the contents of stream.
fread returns the number of items read.
fwrite appends at most nitems items of data from the array pointed to by
ptr to the named output stream. fwrite stops appending when it has
appended nitems items of data or if an error condition is encountered on
stream. fwrite does not change the contents of the array pointed to by
ptr. fwrite increments the data-printer in the stream by the number of
bytes written. If an error occurs, the resulting value of the file-
position indicator for the stream is indeterminate. fwrite returns the
number of items written.
ferror(3S) may be used to determine if an error occurred in an fread or
fwrite call. The ferror(3S) or feof(3S) routines should be used to
distinguish between an error condition and end-of-file condition.
The argument size is typically sizeof(*ptr) where the C operator sizeof
is used to determine the length of an item pointed to by ptr.
SEE ALSOexit(2), fcntl(2), lseek(2), read(2), write(2), abort(3C), fclose(3S),
fopen(3S), ferror(3S), getc(3S), gets(3S), printf(3S), putc(3S),
puts(3S), scanf(3S), stdio(3S).
NOTE
To use these functions with direct I/O (see fcntl(2)), it is necessary to
arrange that the buffers be correctly aligned before any I/O is done.
One way to do this is:
char *caBuffer11;
caBuffer11 = memalign(dioinfo.d_mem, 8+100 * dioinfo.d_miniosz);
setbuffer(fpOutFile,caBuffer11,8+100 * dioinfo.d_miniosz);
where the dioinfo structure has been filled in by the F_DIOINFO fcntl
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FREAD(3S)FREAD(3S)
request.
DIAGNOSTICS
Both fread and fwrite always return a nonnegative integer indicating the
number of items read or written. This will be equal to nitems unless an
error occurred, the value of size is zero, or fread or fwrite detect that
a request has been made to read (or write) more data than is addressable.
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