Function parameter in c++
-
void f(int i) {}-- this function expects to get one int parameter and returns nothing. -
void f(int *i){}-- this one is waiting for a pointer, I understand. -
void f(int &i){}-- what does this function expect at the input?
2 answers
In short, we can say the following.
The parameter of this function is
Void f(int &i){}
Defines a so-called lvalue reference.
This function definition allows you to change the argument passed to the function, since the function is not passed a copy of the argument value, but the argument is passed by reference. For example,
#include <iostream>
void g( int i )
{
i += 10;
}
void h( int &i )
{
i += 10;
}
int main()
{
int i = 0;
std::cout << "Before call g( i ) i = " << i << '\n';
g( i );
std::cout << "After call g( i ) i = " << i << '\n';
std::cout << '\n';
std::cout << "Before call h( i ) i = " << i << '\n';
h( i );
std::cout << "After call h( i ) i = " << i << '\n';
return 0;
}
Program output to the console
Before call g( i ) i = 0
After call g( i ) i = 0
Before call h( i ) i = 0
After call h( i ) i = 10
That is, the function g deals with a copy of the value of the variable i. The original one itself the i variable declared in main does not change.
On the other hand, the function h modifies the original variable i, since it is passed to the function by reference.
Keep in mind that you can also declare a function parameter as
int &&i
This is a so-called rvalue reference designed for working with temporary objects.
Consider such a program.
#include <iostream>
void f( int && )
{
std::cout << "void f( int && )\n";
}
void f( int * )
{
std::cout << "void f( int * )\n";
}
void f( int & )
{
std::cout << "void f( int & )\n";
}
int main()
{
int i = 0;
f( 0 );
f( i );
f( &i );
return 0;
}
Its output to the console:
void f( int && )
void f( int & )
void f( int * )
Short answer: this function expects an lvalue of type int. Parameter-link i will be bound to the lvalue that you pass as an argument.
Long answer: Read the literature on references in C++. References in C++ are a basic property of the C++ language and are too broad a topic to attempt to cover in a single answer.
What is the difference between references and pointers in C++