问题
As seen on ideone:
cout << string(50, 'x'); // xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
cout << string{50, 'x'}; // 2x
WAT??
I have figured out that 50 is ASCII '2', so:
cout << static_cast<int>('2'); // 50
cout << static_cast<char>(50); // 2
But that's as far as I've got.
Does this lead to a solid argument against C++11 initializers?
回答1:
When you do string { 50, 'x' } you're essentially initializing the string with a list of characters.
On the other hand, string(50, 'x') calls a 2 argument constructor, which is defined to repeat the character x 50 times. The reason why string { 50, 'x' } doesn't pick the constructor is that it could be ambiguous. What if you had a three parameter constructor as well? If the type has an initializer_list constructor, it will be picked when you use { ... } for initialization.
Basically you need to be aware of the constructors your type has. The initializer_list constructor will always have a precedence to avoid ambiguity.
来源：https://stackoverflow.com/questions/27063811/c11-string50-x-versus-string50-x