[edited] what does ':' do in following statement ?

Question

What is the use of ':" in c++?
Line no 4/5

See code below
https://code.sololearn.com/c2AJkrtgP9W9/?ref=app

Or

auto msg : messages; //this line

Answer 1

Where is the code?

Answer 2

It's member initializer. It's used to initialize the class members. https://www.sololearn.com/learn/CPlusPlus/1896/

Answer 3

I know , but I am taking about ':' after initializer

Answer 4

That's the syntax of it. member(value)

Saying you have a class:

class A {
private:
int n;
};

You can initialize n in the constructor with:

A(int number): n(number) {}