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   fwrite    ( 3 )

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Имя (Name)

fread, fwrite - binary stream input/output

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Синопсис (Synopsis)

#include <stdio.h>

       size_t fread(void *restrict ptr, size_t size, size_t nmemb,
                    FILE *restrict stream);
       size_t fwrite(const void *restrict ptr, size_t size, size_t nmemb,
                    FILE *restrict stream);

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Описание (Description)

The function fread() reads nmemb items of data, each size bytes
       long, from the stream pointed to by stream, storing them at the
       location given by ptr.

       The function fwrite() writes nmemb items of data, each size bytes
       long, to the stream pointed to by stream, obtaining them from the
       location given by ptr.

       For nonlocking counterparts, see unlocked_stdio(3).

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Возвращаемое значение (Return value)

On success, fread() and fwrite() return the number of items read
       or written.  This number equals the number of bytes transferred
       only when size is 1.  If an error occurs, or the end of the file
       is reached, the return value is a short item count (or zero).

       The file position indicator for the stream is advanced by the
       number of bytes successfully read or written.

       fread() does not distinguish between end-of-file and error, and
       callers must use feof(3) and ferror(3) to determine which
       occurred.

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Атрибуты (Attributes)

For an explanation of the terms used in this section, see
       attributes(7).

       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │Interface                             │ Attribute     │ Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │fread(), fwrite()                     │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

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Стандарты (Conforming to)

POSIX.1-2001, POSIX.1-2008, C89.

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Примеры (Examples)

The program below demonstrates the use of fread() by parsing
       /bin/sh ELF executable in binary mode and printing its magic and
       class:

           $ ./a.out
           ELF magic: 0x7f454c46
           Class: 0x02

   Program source

       #include <stdio.h>
       #include <stdlib.h>

       #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))

       int
       main(void)
       {
           FILE *fp = fopen("/bin/sh", "rb");
           if (!fp) {
               perror("fopen");
               return EXIT_FAILURE;
           }

           unsigned char buffer[4];

           size_t ret = fread(buffer, sizeof(*buffer), ARRAY_SIZE(buffer), fp);
           if (ret != ARRAY_SIZE(buffer)) {
               fprintf(stderr, "fread() failed: %zu\n", ret);
               exit(EXIT_FAILURE);
           }

           printf("ELF magic: %#04x%02x%02x%02x\n", buffer[0], buffer[1],
                  buffer[2], buffer[3]);

           ret = fread(buffer, 1, 1, fp);
           if (ret != 1) {
               fprintf(stderr, "fread() failed: %zu\n", ret);
               exit(EXIT_FAILURE);
           }

           printf("Class: %#04x\n", buffer[0]);

           fclose(fp);

           exit(EXIT_SUCCESS);
       }

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Смотри также (See also)

read(2), write(2), feof(3), ferror(3), unlocked_stdio(3)

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