Binary search with returned index in STL?

Question

I need a binary search function.

I couldn\'t find any function in the standard library that will return the index of the found item, and if it wasn\'t found,

Answer 1

int a = 0, b = n-1;
while (a <= b) {
    int k = (a+b)/2;
    if (array[k] == x) 
    {
        // x found at index k
    }
    if (array[k] < x) a = k+1;
    else b = k-1;
}