Casting a byte stream to a struct

The code

Embedded C for Cortex-M. It compiles. There are 4 real bugs in it: the kind that pass a bench test and fail in the field.

typedef struct {
    uint8_t  type;
    uint32_t length;
    uint16_t crc;
} frame_hdr_t;

void on_frame(const uint8_t *buf, size_t len)
{
    if (len < sizeof(frame_hdr_t)) return;
    const frame_hdr_t *h = (const frame_hdr_t *)buf;
    uint32_t n = h->length;
    process(buf + sizeof(frame_hdr_t), n);
}

What an interviewer expects

• Point to each line you'd stop in a code review.
• Say what actually breaks: the failure mode, not just the rule it violates.
• Fix it, then defend the fix when asked the follow-up.

The bugs, reference fixes and the follow-up question are in the practice app, after you've tried it.

Companies that test this

Matched on the skills each company's embedded roles emphasise.

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