Multiply vector elements by a scalar value using STL

Question

Hi I want to (multiply,add,etc) vector by scalar value for example myv1 * 3 , I know I can do a function with a forloop , but is there a way of doing this using STL function? Something like the {Algorithm.h :: transform function }?

Answer 1

Yes, using std::transform:

std::transform(myv1.begin(), myv1.end(), myv1.begin(),                std::bind(std::multiplies<T>(), std::placeholders::_1, 3)); 

Before C++17 you could use std::bind1st(), which was deprecated in C++11.

std::transform(myv1.begin(), myv1.end(), myv1.begin(),                std::bind1st(std::multiplies<T>(), 3)); 

For the placeholders;

#include <functional>  

Answer 2

If you can use a valarray instead of a vector, it has builtin operators for doing a scalar multiplication.

v *= 3; 

If you have to use a vector, you can indeed use transform to do the job:

transform(v.begin(), v.end(), v.begin(), _1 * 3); 

(assuming you have something similar to Boost.Lambda that allows you to easily create anonymous function objects like _1 * 3 :-P)