Read a fixed-size record

Challenge

Your job

#include <stdint.h>
#include <stddef.h>
int read_record(const uint8_t *buf, size_t n, size_t recsize, int idx, unsigned char *out);

Copy the idx-th recsize-byte record from buf into out. Return 0 on success, or -1 on NULL, recsize == 0, negative idx, or a record that runs past n.

Hints

1. The record starts at idx * recsize.
2. Verify start + recsize <= n before copying.

Why this matters

Binary formats (databases, MFT, packet logs) are arrays of fixed-size records; reading record N is just bounds-checked indexing.

Starter code

#include <stdint.h>
#include <stddef.h>
int read_record(const uint8_t *buf, size_t n, size_t recsize, int idx, unsigned char *out) {
    /* TODO */
    (void)buf; (void)n; (void)recsize; (void)idx; (void)out;
    return -1;
}

Common mistakes

Integer overflow on idx×recsize (guard with the bound check). Off-by-one letting the last record read past n.

Edge cases to handle

Last valid record. idx one past the end. recsize 0.

Complexity

O(recsize).

Background lessons

• Binary files
• fread for binary I/O