Safe strncpy Implementation

Medium C Robustness Asked at Cisco

The standard strncpy does not always null-terminate, which is a classic source of buffer overruns. Write a safe variant that always terminates and reports truncation.

Constraints

Signature: `int safe_strcpy(char *dst, size_t dst_size, const char *src)`.
Returns 0 on success, -1 if the source was truncated, -2 on invalid arguments.
dst must always be null-terminated when dst_size > 0.
Must not write more than dst_size bytes.
No libc string functions.
dst_size == 0 must write nothing at all.

Starter codeC

1#include <stddef.h>2 3int safe_strcpy(char *dst, size_t dst_size, const char *src) {4    // TODO5    return -2;6}