двоичный вход (binary input)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
fread — binary input
Синопсис (Synopsis)
#include <stdio.h>
size_t fread(void *restrict ptr, size_t size, size_t nitems,
FILE *restrict stream);
Описание (Description)
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 POSIX.1‐2017 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 of unsigned 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.
The fread() function may mark the last data access timestamp of
the file associated with stream for update. The last data access
timestamp shall be marked for update by the first successful
execution of fgetc(), fgets(), fread(), fscanf(), getc(),
getchar(), getdelim(), getline(), gets(), or scanf() using stream
that returns data not supplied by a prior call to ungetc().
Возвращаемое значение (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, and
errno shall be set to indicate the error.
Ошибки (Error)
Refer to fgetc(3p).
The following sections are informative.
Примеры (Examples)
Reading from a Stream
The following example transfers a single 100-byte fixed length
record from the fp stream into the array pointed to by buf.
#include <stdio.h>
...
size_t elements_read;
char buf[100];
FILE *fp;
...
elements_read = fread(buf, sizeof(buf), 1, fp);
...
If a read error occurs, elements_read will be zero but the number
of bytes read from the stream could be anything from zero to
sizeof(buf)-1.
The following example reads multiple single-byte elements 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, 1, sizeof(buf), fp);
...
If a read error occurs, bytes_read will contain the number of
bytes read from the stream.
Использование в приложениях (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.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
Section 2.5, Standard I/O Streams, feof(3p), ferror(3p),
fgetc(3p), fopen(3p), fscanf(3p), getc(3p), gets(3p)
The Base Definitions volume of POSIX.1‐2017, stdio.h(0p)
