C++ Constant structure member initialization

Question

I\'ve a constant struct timespec member in my class. How am I supposed to initialize it?

The only crazy idea I got is to derive my own timespec

Answer 1

Use an initialization list with a helper function:

#include <iostream>
#include <time.h>
#include <stdexcept>

class Foo
{
    private:
        const timespec bar;

    public:
        Foo ( void ) : bar ( build_a_timespec() )
        {

        }
    timespec build_a_timespec() {
      timespec t;

      if(clock_gettime(CLOCK_REALTIME, &t)) {
        throw std::runtime_error("clock_gettime");
      }
      return t;
    }
};


int main() {
    Foo foo;    
    return 0;
}

Answer 2

Use initialization list

class Foo
{
    private:
        const timespec bar;

    public:
        Foo ( void ) :
            bar(100)
        { 

        }
};

If you want to initialize structure with bracers then use them

Foo ( void ) : bar({1, 2})

Answer 3

In C++11, you can initalise an aggregate member in the constructor's initialiser list:

Foo() : bar{1,1} {}

In older versions of the language, you would need a factory function:

Foo() : bar(make_bar()) {}

static timespec make_bar() {timespec bar = {1,1}; return bar;}