CODEWITHSUNDEEP
c++11initializationstdvector
srking
srking

Reputation: 4732

C++11 efficient vector member initialization?

What is the best way to initialize a vector member object in C++11? Will the compiler optimize away the copy in foo or will bar be more efficient?

#include <vector>
using namespace std;

// C++11 style
struct foo
{
        vector<int> vec = vector<int>(256);
};

// traditional
struct bar
{
        bar() : vec(256) {}
        vector<int> vec;
};

Upvotes: 1

Views: 128

Answers (1)

Aaron McDaid
Aaron McDaid

Reputation: 27133

In C++11 there probably isn't much difference between them. For example foo does not copy a large vector. The right hand side of the = is an rvalue and will be moved to the left hand side. The only difference is the creation (and quick removal) of the 0-element vector within foo. But that'll take up no time.

But, both C++11 and C++03 allow optimizations ('elision') to skip the assignment in foo. Therefore they can both be very efficient in both standards.

Upvotes: 1

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