Optimal way to convert an int into a char array

Question

What is the best method (performance) to put an int into a char array? This is my current code:

data[0] = length & 0xff;
data[1] = (length >> 8)  & 0xff;
data[2] = (length >> 16) & 0xff;
data[3] = (length >> 24) & 0xff;

data is a char array (shared ptr) and length is the int.

Answer 1

Are you looking for memcpy

char x[20];
int a;
memcpy(&a,x,sizeof(int));

Your solution is also good as it is endian safe.

On a side note:-

Although there is no such guarantee that sizeof(int)==4 for any particular implementation.

Answer 2

Just use reinterpret_cast. Use the data array as if it were an int pointer.

    char data[sizeof(int)];
    *reinterpret_cast<int*>(data) = length;

BTW memcpy is much slower than this, because it copies byte by byte using a loop.
In the case of an integer, this will just be a straightforward assignment.