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Pass by reference VS pass by pointer

Whats the difference between two in C++?

25th Feb 2019, 7:03 AM
Abhay Jindal
Abhay Jindal - avatar
2 Answers
+ 9
A reference variable is an alias of an existing variable. int a = 39; int& b = a; // both a and b refer to the same variable. A pointer is a variable which stores the address of another variable, int a = 39; int* b = &a; While both pass-by-reference and pass-by-pointer may be done due the same purpose, i.e. to change the value of the variable passed as a parameter to the function, within the function body, there are some subtle differences, such as the need to dereference a pointer in the function body. void change1(int* a) { *a = 39; // dereference the pointer before altering the value } void change2(int& a) { a = 39; // alter the reference variable } int main() { int a1 = 38, a2 = 38; change1(&a1); // pass address of a1 change2(a2); // pass a2 directly }
25th Feb 2019, 7:24 AM
Fermi
Fermi - avatar
+ 1
A practical recommendation I have read: When you want to change the value you pass, use a pointer; when you just want to read the data, use a reference but make it const. The point was to keep your code maintainable. A call by value looks exactly like a call by reference: f(x) So by just calling the function you can't tell if it has the power to mess around with the original variable or not. A call by pointer looks differently: f(&x) So here you explicitly and knowingly you grant the function the right to modify x.
25th Feb 2019, 9:20 AM
HonFu
HonFu - avatar