1FREAD(3P) POSIX Programmer's Manual FREAD(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 fread - binary input
13
15 #include <stdio.h>
16 size_t fread(void *restrict ptr, size_t size, size_t nitems,
18 FILE *restrict stream);
19
22 The fread() function shall read into the array pointed to by ptr up to
23 nitems elements whose size is specified by size in bytes, from the
24 stream pointed to by stream. For each object, size calls shall be made
25 to the fgetc() function and the results stored, in the order read, in
26 an array of unsigned char exactly overlaying the object. The file posi‐
27 tion indicator for the stream (if defined) shall be advanced by the
28 number of bytes successfully read. If an error occurs, the resulting
29 value of the file position indicator for the stream is unspecified. If
30 a partial element is read, its value is unspecified.
31 The fread() function may mark the st_atime field of the file associated
33 with stream for update. The st_atime field shall be marked for update
34 by the first successful execution of fgetc(), fgets(), fgetwc(),
35 fgetws(), fread(), fscanf(), getc(), getchar(), gets(), or scanf()
36 using stream that returns data not supplied by a prior call to ungetc()
37 or ungetwc().
38
40 Upon successful completion, fread() shall return the number of elements
41 successfully read which is less than nitems only if a read error or
42 end-of-file is encountered. If size or nitems is 0, fread() shall
43 return 0 and the contents of the array and the state of the stream
44 remain unchanged. Otherwise, if a read error occurs, the error indica‐
45 tor for the stream shall be set, and errno shall be set to indicate
46 the error.
47
49 Refer to fgetc().
50 The following sections are informative.
52
54 Reading from a Stream
55 The following example reads a single element from the fp stream into
56 the array pointed to by buf.
57 #include <stdio.h>
60 ...
61 size_t bytes_read;
62 char buf[100];
63 FILE *fp;
64 ...
65 bytes_read = fread(buf, sizeof(buf), 1, fp);
66 ...
67
69 The ferror() or feof() functions must be used to distinguish between an
70 error condition and an end-of-file condition.
71 Because of possible differences in element length and byte ordering,
73 files written using fwrite() are application-dependent, and possibly
74 cannot be read using fread() by a different application or by the same
75 application on a different processor.
76
78 None.
79
81 None.
82
84 feof(), ferror(), fgetc(), fopen(), getc(), gets(), scanf(), the Base
85 Definitions volume of IEEE Std 1003.1-2001, <stdio.h>
86
88 Portions of this text are reprinted and reproduced in electronic form
89 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
90 -- Portable Operating System Interface (POSIX), The Open Group Base
91 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
92 Electrical and Electronics Engineers, Inc and The Open Group. In the
93 event of any discrepancy between this version and the original IEEE and
94 The Open Group Standard, the original IEEE and The Open Group Standard
95 is the referee document. The original Standard can be obtained online
96 at http://www.opengroup.org/unix/online.html .
97IEEE/The Open Group 2003 FREAD(3P)