Guard clauses in C

Validate at the top and return early, so the body has no nesting left.

int copy_bounded(char *dst, size_t cap, const char *src, size_t *written) {
    if (dst == NULL || src == NULL || cap == 0) {
        return 0;
    }
    size_t n = strlen(src);
    if (n + 1 > cap) {
        return 0;
    }
    memcpy(dst, src, n + 1);
    if (written != NULL) {
        *written = n;
    }
    return 1;
}

How it works

1. A NULL check at the entrance beats a crash deep inside.
2. Early returns keep the happy path at one indent level.
3. The checks double as documentation of the contract.

Keywords and builtins used here

• NULL
• char
• const
• copy_bounded
• if
• int
• return
• size_t

The run, in numbers

Lines

14

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264

Tokens

94

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Type this snippet

Step 2 of 4 in Signatures, step 2 of 11 in APIs, errors & testing.

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