{"id":7348,"date":"2022-12-20T19:37:46","date_gmt":"2022-12-20T22:37:46","guid":{"rendered":"http:\/\/lode.uno\/linux-man\/index.php\/2022\/12\/20\/fread-man3\/"},"modified":"2022-12-20T19:37:46","modified_gmt":"2022-12-20T22:37:46","slug":"fread-man3","status":"publish","type":"post","link":"https:\/\/lode.uno\/linux-man\/2022\/12\/20\/fread-man3\/","title":{"rendered":"FREAD (man3)"},"content":{"rendered":"

FREAD<\/h1>\n

NAME<\/a>
SYNOPSIS<\/a>
DESCRIPTION<\/a>
RETURN VALUE<\/a>
ATTRIBUTES<\/a>
CONFORMING TO<\/a>
EXAMPLES<\/a>
SEE ALSO<\/a>
COLOPHON<\/a> <\/p>\n

\n

NAME <\/a> <\/h2>\n

fread, fwrite \u2212 binary stream input\/output<\/p>\n

SYNOPSIS <\/a> <\/h2>\n

#include <\/b><\/p>\n

size_t fread(void *<\/b>ptr<\/i>, size_t<\/b> size<\/i>, size_t<\/b> nmemb<\/i>, FILE *<\/b>stream<\/i>);<\/b><\/p>\n

size_t fwrite(const void *<\/b>ptr<\/i>, size_t<\/b> size<\/i>, size_t<\/b> nmemb<\/i>,
FILE *<\/b>stream<\/i>);<\/b><\/p>\n

DESCRIPTION <\/a> <\/h2>\n

The function fread<\/b>() reads nmemb<\/i> items of data, each size<\/i> bytes long, from the stream pointed to by stream<\/i>, storing them at the location given by ptr<\/i>.<\/p>\n

The function fwrite<\/b>() writes nmemb<\/i> items of data, each size<\/i> bytes long, to the stream pointed to by stream<\/i>, obtaining them from the location given by ptr<\/i>.<\/p>\n

For nonlocking counterparts, see unlocked_stdio<\/b>(3).<\/p>\n

RETURN VALUE <\/a> <\/h2>\n

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

The file position indicator for the stream is advanced by the number of bytes successfully read or written.<\/p>\n

fread<\/b>() does not distinguish between end-of-file and error, and callers must use feof<\/b>(3) and ferror<\/b>(3) to determine which occurred.<\/p>\n

ATTRIBUTES <\/a> <\/h2>\n

For an explanation of the terms used in this section, see attributes<\/b>(7).<\/p>\n\n\n\n
<\/td>\n <\/td>\n <\/td>\n<\/td>\n<\/td>\n <\/td>\n<\/tr>\n
<\/td>\n<\/td>\n <\/td>\n<\/td>\n<\/td>\n <\/td>\n<\/tr>\n<\/table>\n

\"Image<\/p>\n

CONFORMING TO <\/a> <\/h2>\n

POSIX.1-2001, POSIX.1-2008, C89.<\/p>\n

EXAMPLES <\/a> <\/h2>\n

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

$ .\/a.out<\/b>
ELF magic: 0x7f454c46
Class: 0x02<\/p>\n

Program source<\/b>
#include
#include <\/p>\n

#define ARRAY_SIZE(arr) (sizeof(arr) \/ sizeof((arr)[0]))<\/p>\n

int
main(void)
{
FILE *fp = fopen(“\/bin\/sh”, “rb”);
if (!fp) {
perror(“fopen”);
return EXIT_FAILURE;
}<\/p>\n

unsigned char buffer[4];<\/p>\n

size_t ret = fread(buffer, ARRAY_SIZE(buffer), sizeof(*buffer), fp);
if (ret != sizeof(*buffer)) {
fprintf(stderr, “fread() failed: %zun”, ret);
exit(EXIT_FAILURE);
}<\/p>\n

printf(“ELF magic: %#04x%02x%02x%02xn”, buffer[0], buffer[1],
buffer[2], buffer[3]);<\/p>\n

ret = fread(buffer, 1, 1, fp);
if (ret != 1) {
fprintf(stderr, “fread() failed: %zun”, ret);
exit(EXIT_FAILURE);
}<\/p>\n

printf(“Class: %#04xn”, buffer[0]);<\/p>\n

fclose(fp);<\/p>\n

exit(EXIT_SUCCESS);
}<\/p>\n

SEE ALSO <\/a> <\/h2>\n

read<\/b>(2), write<\/b>(2), feof<\/b>(3), ferror<\/b>(3), unlocked_stdio<\/b>(3)<\/p>\n

COLOPHON <\/a> <\/h2>\n

This page is part of release 5.10 of the Linux man-pages<\/i> project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https:\/\/www.kernel.org\/doc\/man\u2212pages\/.<\/p>\n

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