tim tim - 1 year ago 110
C++ Question

Difference between function arguments declared with & and * in C++

I typed the following example:

#include <iostream>
double f(double* x, double* y)
std::cout << "val x: " << *x << "\n";
std::cout << "val y: " << *y << "\n";
return *x * *y;
double f2(double &x, double &y)
std::cout << "val x: " << x << "\n";
std::cout << "val y: " << y << "\n";
return x * y;
int main()
double a, b;
a = 2;
b = 3;
std::cout << f(&a, &b) << "\n";
std::cout << f2(a, b) << "\n";
return 0;

In the function
I declare x and y as pointers of which I can get the value by using
. When calling
I need to pass the address of my passed arguments, that is why I pass
&a, &b
is the same except the definition is different.

Now my question is: Are they both really the same concerning memory management? Both not making any copy of the passed value but instead passing a reference?
I wonder about
because I couldn't read out the address of
so I know more about x and y in
(there I know address AND value).

Thanks in advance!

Edit: Okay thanks, after doing some more research, I found a quite useful topic:

Pointer vs. Reference
There's also a link to google coding guidelines http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Reference_Arguments which is quite
I feel (as I understood now, it's a form of subject taste) to make more clear

Answer Source

f2 is taking it's arguments by reference, which is essentially an alias for the arguments you pass. The difference between pointer and reference is that a reference cannot be NULL. With the f you need to pass the address (using & operator) of the parameters you're passing to the pointer, where when you pass by reference you just pass the parameters and the alias is created.

Passing by const reference (const double& ref) is preferred when you are not going to change the arguments inside the function, and when you are going to change them, use non-const reference.

Pointers are mostly used when you need to be able to pass NULL to your parameters, obviously you'd need to check then inside your function if the pointer was not NULL before using it.

Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download