How can I declare and define multiple variables in one line using C++?

Question

I always though that if I declare these three variables that they will all have the value 0

int column, row, index = 0;

Bu

Answer 1

When you declare:

int column, row, index = 0;

Only index is set to zero.

However you can do the following:

int column, row, index;
column = index = row = 0;

But personally I prefer the following which has been pointed out.
It's a more readable form in my view.

int column = 0, row = 0, index = 0;

or

int column = 0;
int row = 0;
int index = 0;

Answer 2

When you declare a variable without initializing it, a random number from memory is selected and the variable is initialized to that value.

Answer 3

int column = 0, row = 0, index = 0;

Answer 4

Possible approaches:

• Initialize all local variables with zero.
• Have an array, memset or {0} the array.
• Make it global or static.
• Put them in struct, and memset or have a constructor that would initialize them to zero.

Answer 5

As others have mentioned, from C++17 onwards you can make use of structured bindings for multiple variable assignments.

Combining this with std::array and template argument deduction we can write a function that assigns a value to an arbitrary number of variables without repeating the type or value.

#include <iostream>
#include <array>

template <int N, typename T> auto assign(T value)
{
    std::array<T, N> out;
    out.fill(value);
    return out;
}

int main()
{
    auto [a, b, c] = assign<3>(1);

    for (const auto& v : {a, b, c})
    {
        std::cout << v << std::endl;
    }

    return 0;
}

Demo

Answer 6

int column(0), row(0), index(0);

Note that this form will work with custom types too, especially when their constructors take more than one argument.