Reusing String in C++ in function [closed]

Question

As someone whose main language has been Python so far, I have a problem with string reuse.

Here's an example code (simplified):

void function(std::string &basicString) 
{
std::cout << "Function print: " << &basicString << "\n";
}

int main() 
{
std::vector<std::string> x_files;
/*
Does sth, x_files contains some strings
*/

for (std::vector<std::string>::size_type i = 0; i != x_files.size(); i++) {
    std::string temp = x_files[i];
    std::cout << temp << "\n";
    function(temp);
}
return 0;
}

The thing is, as a result I'd like to have this:

my_string
Function print: my_string

Instead, I get this:

my_string
Function print: 0x7cd2346eaf1827cd

0x7cd2346eaf1827cd - not exactly what I get every time, but an example.

Answer 1

std::cout << "Function print: " << &basicString << "\n";

Here you use unary & operator, which is an address-of operator, in other words it gives you a pointer. And since this is not a char pointer, std::cout prints the pointer value, in other words a memory address, as hex.

Solution is simple, remove &:

std::cout << "Function print: " << basicString << "\n";

---

Perhaps you're getting confused about pointers, because if instead of reference you used a pointer, you'd do this:

void function(std::string *basicString) 
{
    std::cout << "Function print: " << *basicString << "\n";
}

Pointers and references are quite similar, but they are not the same, including this difference in how they are declared and used.

---

Finally, you probably want to pass a const reference:

void function(const std::string &basicString)

You should always use const with a reference parameter, unless you intend to modify the original.

Answer 2

C++(like many other) is a context based language. For example, in you given snippet, when you wrote:

void function(std::string &basicString) //here basicString is a lvalue reference to std::string
{

}

In the above snippet, you're defining a function named function that take one parameter whose type is an lvalue reference to a std::string. That is, the & symbol represents an lvalue reference in this context.

On the other hand, when you wrote:

std::cout << "Function print: " << &basicString << "\n";

Here the & symbol means that you're taking the address of the variable to which basicString refers.

Solution

To solve this you just have to remove the & symbol as shown below:

void function(std::string &basicString) //NO NEED TO REMOVE & FROM HERE
{
std::cout << "Function print: " << basicString << "\n"; //REMOVED & FROM HERE
}