这种类型的声明在 c++ 中意味着什么？

Question

I can't understand this; please describe it. This is C++ code:

int upper(0), lower(0);

Answer 1

As noted in @dxiv's comment, this is direct initialization of the upper and lower variables. The following syntax is also direct initialization:

int even_lower{0};

when applied to non-class type objects. When applied to objects of class type, it invokes the relevant constructor or conversion operator.

Answer 2

I will try to add all possible ways to assign a variable in here with the difference

1

int upper=0, lower=0;
will assign upper as 0 and lower as 0

2 constructor initialization with single value

int upper(0), lower(0);
will assign upper as 0 and lower as 0

3 constructor initialization with multiple values will initialize a variable with the last value

int upper=(0,1,2,3), lower=(44,55,6,77,-5);
will assign upper as 3 and lower as -5

4 Uniform Initialization takes only single value you can't have multiple values in here

int upper{0}, lower{0};
will assign upper as 0 and lower as 0

5 you can use = in both constructor and uniform initialization for single values

int upper={0}, lower={0};
will assign upper as 0 and lower as 0