Pass by Pointer * or Pass by Reference &?

[Robert]

Hello all,

I am a C programmer learning C++. And I am confused with function Pass
by Pointer * or Pass by Reference &.

Function pass by pointer like:
void func(int * x)
And function pass by referencelike:
void func(int & x)

What's their main difference and be used in what circumstance?

Best regards,
Robert

[E. Robert Tisdale]

Robert wrote:

Another problem is
why reference cannot be able to represent [an invalid] object? cat main.cc #include <iostream>

void f(const int& r) {
if (0 == &r) { // undefined behavior
std::cout << "&r = " << &r << std::endl;
}
else {
std::cout << "r = " << r << std::endl;
}
}

int main(int argc, char* argv[]) {

int* p = 0;
int& r = *p; // undefined behavior
f(r);

return 0;
}
g++ -Wall -ansi -pedantic -o main main.cc
./main

&r = 0

Beware!
A reference *can* represent an invalid object
but the behavior is undefined.