#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);
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).
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.
| Interface | Attribute | Value |
| fread(), fwrite() | Thread safety | MT-Safe |
$ ./a.out ELF magic: 0x7f454c46 Class: 0x02
#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);