Why we cannot initialize the member variable of a class in C++

Question

It's giving error:

#include <iostream>
using std::cout;

class stud
{
    int a = 0; // error??

public:
    void display();
};

int main()
{
    // ...
}

Answer 1

(The cause)

Non-static data member with a default member initializer is supported since C++11.

--

(The fix)

These days, many compilers support C++11.

For Visual Studio IDE users (like myself): On project properties: C/C++ > Language > C++ Language Standard: Set to C++11 or above. In Visual Studio 2017 C++11 is supported at baseline.

For other than Visual Studio IDE users, search the topic: "How to enable C++11" for your compiler.

Answer 2

It is possible to do this from C++11 onwards.

Through a default member initializer, which is simply a brace or equals initializer included in the member declaration, which is used if the member is omitted in the member initializer list.

class S
{
    int n = 7;
    std::string s{'a', 'b', 'c'};
    S() // copy-initializes n, list-initializes s
    { }
};