I decided to see if assigning a reference to a member would make a member a reference. I wrote the following snippet to test it. There's a simple class Wrapper
with an std::string
as a member variable. I take take a const string&
in the constructor and assign it to the public member variable. Later in the main()
method I modify the member variable but the string
I passed to the constructor remains unchanged, how come? I think in Java the variable would have changed, why not in this code snippet? How exactly do references work in this case?
#include <iostream>
#include <string>
using namespace std;
class Wrapper
{
public:
string str;
Wrapper(const string& newStr)
{
str = newStr;
}
};
int main (int argc, char * const argv[])
{
string str = "hello";
cout << str << endl;
Wrapper wrapper(str);
wrapper.str[0] = 'j'; // should change 'hello' to 'jello'
cout << str << endl;
}
To assign a reference in a constructor you need to have a reference member
class A{
std::string& str;
public:
A(std::string& str_)
: str(str_) {}
};
str is now a reference to the value you passed in. Same applies for const refs
class A{
const std::string& str;
public:
A(const std::string& str_)
: str(str_) {}
};
However don't forget that once a reference has been assigned it can not be changed so if assignment requires a change to str then it will have to be a pointer instead.