向量之间有什么区别 <int> （）与向量 <int> {} vs NULL vs size = 0？

Question

I want to return an empty vector at the end of my function. Does the following all equivalent? How to understand each of them?

return vector<int>();
return vector<int>{};
return NULL;

The following is my understanding:

1. vector<int>() means creating an empty vector object, which is uninitialized so it's NULL.

2. vector<int>{} means creating an empty vector, which has a size 0.

Is there a difference between size 0 and NULL? Thanks a lot~

Answer 1

The first two are both doing value initialization , and are the same.

NULL is the old backward-compatible symbolic constant for null pointers . C++ doesn't have the concept of "null" values. Unless you return a pointer, it's invalid.

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Regarding NULL , in C++ before the C++11 standard you should really be using 0 for null pointers. And since the C++11 standard you should be using the nullptr literal.