Question

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Intitialzing an array in a C++ class and modifiable lvalue problem

As seen in this question, it’s possible to give a ctor to a struct to make it members get default values. How would you proceed to give a default value to every element of an array inside a struct.

struct foo
{
   int array[ 10 ];
   int simpleInt;
   foo() : simpleInt(0) {}; // only initialize the int...
}

Is there some way to make this in one line similar to how you would do to initialize an int?

Answer 1

Thew new C++ standard has a way to do this:

struct foo
{
   int array[ 10 ];
   int simpleInt;
   foo() : array{1,2,3,4,5,6,7,8,9,10}, simpleInt(0) {};
};

test: https://ideone.com/enBUu

If your compiler does not support this syntax yet, you can always assign to each element of the array:

struct foo
{
   int array[ 10 ];
   int simpleInt;
   foo() : simpleInt(0)
   {
        for(int i=0; i<10; ++i)
            array[i] = i;
   }
};

EDIT: one-liner solutions in pre-2011 C++ require different container types, such as C++ vector (which is preferred anyway) or boost array, which can be boost.assign‘ed

#include <boost/assign/list_of.hpp>
#include <boost/array.hpp>
struct foo
{
    boost::array<int, 10> array;
    int simpleInt;
    foo() : array(boost::assign::list_of(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)),
            simpleInt(0) {};
};