CODEWITHSUNDEEP
c++
C. Binair
C. Binair

Reputation: 451

Why can't I give constant reference of a pointer as function argument

Why does c++ not compile the following?

void func(const int *&pp) 
{ 
    //Do stuff
} 

int main()
{
    int var =23;
    int* ptr_to_var = &var;
    func(ptr_to_var);
}

To clarify I want to pass a pointer as reference to a function, but the pointer should not be changed in the function hence the const.

The compile warning I get is:

error: invalid initialization of reference of type 'const int*&' from expression of type 'int*'

I could do something like this:

void func(int **pp) 
{ 
    //Do stuff
}

But this doesn't give me the exact behavior I would want as now I can actually change the location where the pointer points to, i.e. I miss the const key word.

If you would then do:

void func(const int **pp) 
{ 
    //Do stuff
}

This doesn't compile either and I'm actually not sure that if it would compile it would actually do what I want.

Upvotes: 1

Views: 82

Answers (1)

eerorika
eerorika

Reputation: 238311

Why does c++ not compile the following?

void func(const int *&pp) 
{ 
    //Do stuff
}

This is well-formed, and any standard conforming compiler will compile it.

The compile warning I get is:

error: invalid initialization of reference of type 'const int*&' from expression of type 'int*'

The error message isn't very clear, but I think it is trying to say that you tried to initialise the reference with an rvalue. References to non-const lvalues cannot be bound to rvalues.

If you would then do:

void func(const int **pp) 
{ 
    //Do stuff
}

This doesn't compile either

This is also well-formed, and a standard conforming compiler must accept it.

You can see both examples succesfully compiling here.

Upvotes: 3

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