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.Dd $Mdocdate: May 1 2014 $
.Dt FREAD 3
.Os
.Sh NAME
.Nm fread ,
.Nm fwrite
.Nd binary stream input/output
.Sh SYNOPSIS
.In stdio.h
.Ft size_t
.Fn fread "void *ptr" "size_t size" "size_t nmemb" "FILE *stream"
.Ft size_t
.Fn fwrite "const void *ptr" "size_t size" "size_t nmemb" "FILE *stream"
.Sh DESCRIPTION
The function
.Fn fread
reads
.Fa nmemb
objects, each
.Fa size
bytes long, from the stream pointed to by
.Fa stream ,
storing them at the location given by
.Fa ptr .
.Pp
The function
.Fn fwrite
writes
.Fa nmemb
objects, each
.Fa size
bytes long, to the stream pointed to by
.Fa stream ,
obtaining them from the location given by
.Fa ptr .
.Sh RETURN VALUES
The functions
.Fn fread
and
.Fn 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
.Fa size
or
.Fa nmemb
is 0,
.Fn fread
and
.Fn fwrite
return 0 with no change made to the
.Fa stream .
If the product of
.Fa size
and
.Fa nemb
results in integer overflow, 0 is returned and errno
is set to
.Er EOVERFLOW .
If an error occurs, or the end-of-file is reached,
the return value is a short object count (or zero).
.Pp
The function
.Fn fread
does not distinguish between end-of-file and error, and callers
must use
.Xr feof 3
and
.Xr ferror 3
to determine which occurred.
The function
.Fn fwrite
returns a value less than
.Fa nmemb
only if a write error has occurred.
.Sh SEE ALSO
.Xr read 2 ,
.Xr write 2
.Sh STANDARDS
The functions
.Fn fread
and
.Fn fwrite
conform to
.St -ansiC .
.Sh HISTORY
The functions
.Fn fread
and
.Fn fwrite
first appeared in
.At v7 .