Difference between `int* const& x` and `int* const x` in C++

user_15465454 0
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I've read of the differences between passing by value, passing by reference, and passing (a pointer) by constant reference, yet I'm don't understand the difference between the latter, and just passing a constant pointer. As an example, what is the difference between

int PI = 3;

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

int main() {

}

and

int PI = 3;

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

int main() {

}

Both of these cause the same error: assignment of read-only parameter 'x'.

pointers reference c++
1 Answers

If you're clear on passing variables by value and by reference, then try breaking down complex types into parts to help make sense of what's going on:

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;
}
user_84518140
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