i encountered to this function

void reverseArray(int *a,int n)
{
for(int i=0,j=n-1;i<j;i  ,j--)
{
a[i]^=a[j]^=a[i]^=a[j];
}
}

which is reversing a given array but I can't wrap my mind around how does this reverse an array, isn't Xor operator only returns the non-common bits. so what's the logic behind this to reverse the given array.

CodePudding user response：

a ^= b ^= a ^= b; is a fancy way to swap two numbers, known as XOR swap.

You should prefer a much more readable std::swap, or (in C) a temporary variable.

CodePudding user response：

The purpose of the expression a^=b^=a^=b is to exchange the values of a and b. It becomes more clear if we split it up (where a_0 and b_0 are the original values of a and b):

1. First assignment, a^=b makes a_1=(a_0^b_0).
2. Second assignment, b^=a makes b_1=(b_0^a_1)=(b_0^(a_0^b_0))=a_0
3. Third assignment, a^=b makes a_2=(a_1^b_1)=((a_0^b_0)^a_0)=b_0

Thus we end up with a having the original value of b and vice versa.

While the expression a^=b^=a^=b may work it is actually undefined behavior because the C standard does not specify the order of assignments. Instead, it must be sequenced explicitly: a^=b; b^=a; a^=b;.