1FREAD(P) POSIX Programmer's Manual FREAD(P)
2
6 fread - binary input
7
9 #include <stdio.h>
10 size_t fread(void *restrict ptr, size_t size, size_t nitems,
12 FILE *restrict stream);
13
16 The fread() function shall read into the array pointed to by ptr up to
17 nitems elements whose size is specified by size in bytes, from the
18 stream pointed to by stream. For each object, size calls shall be made
19 to the fgetc() function and the results stored, in the order read, in
20 an array of unsigned char exactly overlaying the object. The file posi‐
21 tion indicator for the stream (if defined) shall be advanced by the
22 number of bytes successfully read. If an error occurs, the resulting
23 value of the file position indicator for the stream is unspecified. If
24 a partial element is read, its value is unspecified.
25 The fread() function may mark the st_atime field of the file associated
27 with stream for update. The st_atime field shall be marked for update
28 by the first successful execution of fgetc(), fgets(), fgetwc(),
29 fgetws(), fread(), fscanf(), getc(), getchar(), gets(), or scanf()
30 using stream that returns data not supplied by a prior call to ungetc()
31 or ungetwc().
32
34 Upon successful completion, fread() shall return the number of elements
35 successfully read which is less than nitems only if a read error or
36 end-of-file is encountered. If size or nitems is 0, fread() shall
37 return 0 and the contents of the array and the state of the stream
38 remain unchanged. Otherwise, if a read error occurs, the error indica‐
39 tor for the stream shall be set, and errno shall be set to indicate
40 the error.
41
43 Refer to fgetc() .
44 The following sections are informative.
46
48 Reading from a Stream
49 The following example reads a single element from the fp stream into
50 the array pointed to by buf.
51 #include <stdio.h>
54 ...
55 size_t bytes_read;
56 char buf[100];
57 FILE *fp;
58 ...
59 bytes_read = fread(buf, sizeof(buf), 1, fp);
60 ...
61
63 The ferror() or feof() functions must be used to distinguish between an
64 error condition and an end-of-file condition.
65 Because of possible differences in element length and byte ordering,
67 files written using fwrite() are application-dependent, and possibly
68 cannot be read using fread() by a different application or by the same
69 application on a different processor.
70
72 None.
73
75 None.
76
78 feof() , ferror() , fgetc() , fopen() , getc() , gets() , scanf() , the
79 Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>
80
82 Portions of this text are reprinted and reproduced in electronic form
83 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
84 -- Portable Operating System Interface (POSIX), The Open Group Base
85 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
86 Electrical and Electronics Engineers, Inc and The Open Group. In the
87 event of any discrepancy between this version and the original IEEE and
88 The Open Group Standard, the original IEEE and The Open Group Standard
89 is the referee document. The original Standard can be obtained online
90 at http://www.opengroup.org/unix/online.html .
91IEEE/The Open Group 2003 FREAD(P)