Example of using memmove in place of memcpy

Question

Difference: If there is an overlap, use memmove in place of memcpy

Q: Could you provide a practical scenario of any C lib function where an overlap happens so memmove is used in place of memcpy?

score 3 · Answer 1 · answered Feb 23 '14 at 21:01

3

For example you need to insert an element in the middle of an array (in-place). This requires shifting the elements from the insertion points onwards by one place. This can be done with memmove() but not with memcpy().

answered Feb 23 '14 at 21:01

NPE

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that is an acceptable, general scenario, but do you remember any from a library function? – codey modey Feb 23 '14 at 21:08
@codeymodey: Have a browse of http://code.ohloh.net/search?s=memmove&pp=0&fe=c&mp=1&ml=1&me=1&md=1&ff=1&filterChecked=true -- there's a ton of real-world examples there. – NPE Feb 23 '14 at 21:11
@codeymodey: Here's an example from the Linux kernel: http://code.ohloh.net/file?fid=LACPbnMYI2RxpXmGAuL1H08qbKk&cid=6NGO2C2fa5k&s=memmove&pp=0&fp=306559&fe=c&ff=1&filterChecked=true&mp=0&ml=1&me=1&md=1#L37 – NPE Feb 23 '14 at 21:13

score 3 · Accepted Answer · answered Feb 23 '14 at 21:09

Here's one:

// len => array length, idx => index where we want to remove
void removeAt(int* array, size_t* len, size_t idx)
{
    // copy next values to replace current
    // example: {1, 2, 3, 4} => {1, 3, 4}
    //              ^ remove
    memmove(&array[idx], &array[idx+1], (--(*len) - idx) * sizeof(int));
}

Edit: Regarding this appearing in the implementation of a C stdlib function, that would be a bit more difficult to find, since each implementation can do their own thing, and most stdlib functions require that the arguments do not overlap.

Example of using memmove in place of memcpy

2 Answers2