Is there a difference between assigning a value to a variable using the equal operator or using curly braces?

Question

I saw a code where a programmer used curly braces to initialize a variable

int var{ 5 };

instead of using the assignment operator

int var = 5;

I know assigning a value to lhs variable using curly braces is a C++11 syntax. Is there any difference between using the two?

Thank you for replies.

Answer 1

They are different kinds of initialization:

T a{b};   // list initialization
T a = b;  // copy initialization
T a(b);   // direct initialization

There is no difference for ints but there can definitely be differences for other types. For instance, copy initialization might fail if your constructor is explicit, whereas the other two would succeed. List initialization disallows narrowing conversions, but for the other two those are fine.

Answer 2

As far as I know, there is no difference in the two for integers. The {} syntax was made to(however, not limited to, because it is also used for initializer_list) prevent programmers from triggering http://en.wikipedia.org/wiki/Most_vexing_parse, and so instead of std::vector<int> v() to initialize v you write std::vector<int> v{};.

The {} has different behaviours depending on the usage, it can be a call to constructor, a initializer list and even a list of values to initialize members of user-defined class in order of definition.

Example of the last:

class Q{
public:
    int a;
    int b;
    float f;
};

int main()
{
    Q q{2, 5, 3.25f};
}