fread (original) (raw)

The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

A newer edition of this document exists here

NAME

fread - binary input

SYNOPSIS

`#include <stdio.h>

size_t fread(void *restrict

ptr, size_t size, size_t nitems,
FILE *restrict stream);
`

DESCRIPTION

[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers to the ISO C standard.

The fread() function shall read into the array pointed to by ptr up to nitems elements whose size is specified by size in bytes, from the stream pointed to by stream. For each object, size calls shall be made to the fgetc() function and the results stored, in the order read, in an array ofunsigned char exactly overlaying the object. The file position indicator for the stream (if defined) shall be advanced by the number of bytes successfully read. If an error occurs, the resulting value of the file position indicator for the stream is unspecified. If a partial element is read, its value is unspecified.

[CX] The_fread_() function may mark the st_atime field of the file associated with stream for update. The_st_atime_ field shall be marked for update by the first successful execution of fgetc(), fgets(), fgetwc(), fgetws(), fread(), fscanf(), getc(), getchar(), gets(), or scanf() using stream that returns data not supplied by a prior call to ungetc() or ungetwc().

RETURN VALUE

Upon successful completion, fread() shall return the number of elements successfully read which is less than_nitems_ only if a read error or end-of-file is encountered. If size or nitems is 0, fread() shall return 0 and the contents of the array and the state of the stream remain unchanged. Otherwise, if a read error occurs, the error indicator for the stream shall be set, [CX] and errno shall be set to indicate the error.

ERRORS

Refer to fgetc().

The following sections are informative.

EXAMPLES

Reading from a Stream

The following example reads a single element from the fp stream into the array pointed to by buf.

#include <stdio.h> ... size_t bytes_read; char buf[100]; FILE *fp; ... bytes_read = fread(buf, sizeof(buf), 1, fp); ...

APPLICATION USAGE

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

Because of possible differences in element length and byte ordering, files written using fwrite() are application-dependent, and possibly cannot be read using fread() by a different application or by the same application on a different processor.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

feof(), ferror(), fgetc(), fopen(), getc(), gets(), scanf(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 6

Extensions beyond the ISO C standard are marked.

The following changes are made for alignment with the ISO/IEC 9899:1999 standard:

• The fread() prototype is updated.
• The DESCRIPTION is updated to describe how the bytes from a call to fgetc() are stored.

End of informative text.

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