# Implement the memcpy() function in C.

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Source: https://www.aced.io/questions/4227/implement-memcpy-function
Source observed: 2026-11-05T00:02:40.324Z
Last checked: 2026-11-05T00:02:40.324+00:00
Indexed: 2026-11-05T20:22:56.639+00:00

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# Implement the `memcpy()` function in C.

This is a Data Structures & Algorithms and Coding interview question associated with the **Software Engineer** role and **Meta**. The page records **1 interview** and says it was last asked **2 years ago**. Detailed company statistics require an [upgrade](https://www.aced.io/upgrade?src=questions).

## Community answers

### Srihitha J.

[Srihitha J.](https://www.aced.io/users/e3c636c2-dc4a-4edb-9b6f-857989170708) — [246 karma](https://www.aced.io/karma); **September 6, 2024**

The answer shown defines `memcpy` with byte-wise copying using `unsigned char` pointers:

```cpp
void* memcpy(void* dest, const void* src, size_t n) {
    unsigned char* uDest = static_cast<unsigned char*>(dest);
    const unsigned char* ucSrc = static_cast<const unsigned char*>(src);
    for (size_t i = 0; i < n; i++) {
        uDest[i] = ucSrc[i];
    }
    return dest;
}
```

The same answer includes a follow-up for byte alignment, copying four bytes at a time and then copying remaining bytes:

```cpp
void* memcpy(void* dest, const void* src, size_t n) {
    unsigned char* uDest = static_cast<unsigned char*>(dest);
    const unsigned char* ucSrc = static_cast<const unsigned char*>(src);

    while (n >= 4) {
        *(reinterpret_cast<unsigned int*>(uDest)) =
            *(reinterpret_cast<const unsigned int*>(ucSrc));
        uDest += 4;
        ucSrc += 4;
        n -= 4;
    }

    // Copy remaining bytes if any
    while (n > 0) {
        *uDest++ = *ucSrc++;
        n--;
    }
    return dest;
}
```

### Kun P.

[Kun P.](https://www.aced.io/users/26c7c17c-5d19-4459-a68c-f5c1756f2240) — [0 karma](https://www.aced.io/karma); **February 24, 2025**

The answer notes that overlapping source and destination ranges require different copy directions:

- If `src` starts before `dst`, start copying from the end.
- If `dst` starts before `src`, start copying from the beginning.

A related comment asks whether the question was for a software engineer virtual or onsite interview and thanks the contributor; it has one more reply.

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