HP-UX Reference (11i v3 07/02) - 3 Library Functions A-M (vol 6)

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fread(3S) fread(3S)

NAME

fread(), fwrite() - buffered binary input/output to a stream ﬁle

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);

Obsolescent Interfaces

size_t fread_unlocked(

void *ptr, size_t size, size_t nitems, FILE *stream);

size_t fwrite_unlocked(

const void *ptr, size_t size, size_t nitems, FILE *stream);

DESCRIPTION

fread() copies, into an array pointed to by ptr,uptonitems 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 appending bytes if an end-of-ﬁle or error condition is encountered while reading stream,or

if nitems items have been read.

fread() leaves the ﬁle pointer in stream, if deﬁned, pointing to the byte

following the last byte read if there is one. fread() does not change the contents of stream.

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.

The argument size is typically

sizeof(*ptr) where the pseudo-function

sizeof speciﬁes the length of

an item pointed to by ptr.

Obsolescent Interfaces

fread_unlocked()

and fwrite_unlocked() buffered binary input/output to a stream ﬁle.

APPLICATION USAGE

After

fread() or fwrite() is applied to a stream, the stream becomes byte-oriented (see orienta-

tion(5)).

RETURN VALUE

fread(), fwrite(), fread_unlocked()

, and fwrite_unlocked() return the number of items

read or written. If size or nitems is 0, no characters are read or written and 0 is returned.

The value returned will be less than nitems only if a read error or end-of-ﬁle is encountered.

When the ﬁle corresponding to an open stream gets extended after the end-of-ﬁle is reached, any subse-

quent calls to

fread() will succeed and the end-of-ﬁle indicator will remain set. However, in the

UNIX2003 standards environment (see standards(5)), this function will return zero and the end-of-ﬁle indi-

cator will remain set.

The ferror() or feof() functions must be used to distinguish between an error condition and an end-

of-ﬁle condition.

ERRORS

Refer to getc(3S) for a description of errors returned by fread().

Refer to putc(3S) for a description of errors returned by fwrite().

WARNINGS

fread_unlocked() and fwrite_unlocked()

are obsolescent interfaces supported only for compa-

tibility with existing DCE applications. New multithreaded applications should use

fread() and

fwrite().