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fshuffle.c
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#include <stdio.h> | |
#include <stdlib.h> | |
#include <string.h> | |
int fswap(FILE *file, off64_t x, off64_t y, size_t size) { | |
unsigned char i[size], o[size]; | |
return fseeko64(file, x * size, SEEK_SET) || fread(i, size, 1, file) != 1 || | |
fseeko64(file, y * size, SEEK_SET) || fread(o, size, 1, file) != 1 || | |
fseeko64(file, y * size, SEEK_SET) || fwrite(i, size, 1, file) != 1 || | |
fseeko64(file, x * size, SEEK_SET) || fwrite(o, size, 1, file) != 1 || | |
|| fflush(file); | |
} | |
int main(int argc, char **argv) { | |
size_t size; | |
if (argc <= 1 || sscanf(argv[1], "%zu", &size) != 1) { | |
puts("Usage: ./app filename"); | |
return EXIT_FAILURE; | |
} | |
FILE *file = fopen(argv[2], "rb+"); | |
if (file == NULL) { | |
puts("Error opening file..."); | |
return EXIT_FAILURE; | |
} | |
off64_t position = 0; | |
for (;;) { | |
unsigned char entry[size]; | |
if (fread(entry, sizeof entry, 1, file) != 1 || fswap(file, position, position ? rand() % position : 0, sizeof entry)) { | |
return ferror(file) ? EXIT_FAILURE : 0; | |
} | |
fwrite(entry, sizeof entry, 1, stdout); | |
position++; | |
} | |
} |
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