Reverse an array with preprocessor - c++

Question

I want to use pre-processor to fill some arrays in some ways. I can use preprocessor only for newly declared arrays. However, I need to change the array p which I declared and used before. Time optimization is very important for my purpose.
#define Reverse(x) {x[63], x[62], x[61], x[60], x[59], x[58], x[57], x[56], x[55], x[54], x[53], x[52], x[51], x[50], x[49], x[48], x[47], x[46], x[45], x[44], x[43], x[42], x[41], x[40], x[39], x[38], x[37], x[36], x[35], x[34], x[33], x[32], x[31], x[30], x[29], x[28], x[27], x[26], x[25], x[24], x[23], x[22], x[21], x[20], x[19], x[18], x[17], x[16], x[15], x[14], x[13], x[12], x[11], x[10], x[9], x[8], x[7], x[6], x[5], x[4], x[3], x[2], x[1], x[0] }
int main()
{
int p[64] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
int q[64] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
//doThings
p= Reverse(q); // line A - Gives error
int s[64] = Reverse(q); // line B - Works properly
//doThings
}
I got this error:
Error 11 error C3079: an initializer-list cannot be used as the right operand of this assignment operator c:\users\ferda\documents\visual studio 2013\projects\consoleapplication3\consoleapplication3\consoleapplication3.cpp 39‌​3 1 ConsoleApplication3

Answer 1

Built in array type does not allow to assign to it another array or use aggregate initialization on already initialized array, you would have to use memcpy or for loop to update it with new values. Your code will compile if you use std::array instead. It provides operator=:
operator= (implicitly declared) overwrites every element of the
array with the corresponding element of another array (public member
function)
http://coliru.stacked-crooked.com/a/8e664210b7f7f73b
i am not sure if this will work as fast as you expect, gcc will generate lots of mov instructions : https://godbolt.org/g/tzUqC3. I suppose it might be faster to use a for loop which will require less cache memory. As always profile your code.