CODEWITHSUNDEEP
c++cpointers
xuma202
xuma202

Reputation: 1084

Increment pointer returned by function

Hey I was experimenting a bit with C/C++ and pointers while reading stuff here

I made myself a function to return a pointer to the int at some place in a global array.

int vals[] = { 5, 1, 45 };

int *  setValue(int k) {
    return &vals[k];
}

However I was able to do this

int* j = setValue(0);
j++;
*j = 7;

to manipulate the array

but that:

*(++setValue(0)) = 42;

din't work. Notice however *setValue(0) = 42; works

From what I understand I call the function and get some pointer I increment it to make it point to the 2nd element in my array. Lastly I deference the pointer and assign a new value to the integer it pointed to.

I find C++ pointers and references can be somewhat confusing but maybe someone can explain me this behavior.

EDIT: This question is NOT a duplicate of Increment, preincrement and postincrement

because it is not about pre- vs. post-increment but rather about increment on pointers that are the return of a function.

EDIT2:

Tweaking the function

int **  setValue(int k) {
    int* x = &vals[k];
    return &x;
}

You can use

*(++(*setValue(1))) = 42;

Upvotes: 3

Views: 807

Answers (1)

Eregrith
Eregrith

Reputation: 4366

You can't call a unary operator (++) on something that is not a variable. setValue(0) is treated as a value.

So,

*(setValue(0)++) = 42;

should be

*(setValue(0) + 1) = 42;

Upvotes: 5

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