c++ - C++中 `int* const& x`和 `int* const x`的区别

Question

我已经阅读了按值传递、按引用传递和按常量引用传递(指针)之间的区别，但我不明白后者与仅传递常量指针之间的区别。举个例子，有什么区别

int PI = 3;

int* getArg(int* const& x){
    x = Π
    return x;
}

int main() {

}

和

int PI = 3;

int* getArg(int* const x){
    x = Π
    return x;
}

int main() {

}

这两个导致相同的 error: assignment of read-only parameter 'x' .

Answer 1

如果您很清楚按值和按引用传递变量，那么请尝试将复杂类型分解为多个部分，以帮助理解发生了什么:

using PointerToInt = int*;
using ConstPointerToInt = PointerToInt const;

int* getArg_v1(ConstPointerToInt x) {
    x = Π  // it's const by value so you're not allowed to change it
    return x;
}

int* getArg_v2(ConstPointerToInt& x) {
    x = Π  // it's const by reference so you're not allowed to change it
    return x;
}