CODEWITHSUNDEEP
c++
Harry
Harry

Reputation: 3032

std::move(std::string) not making passed argument to empty state

I'm bit confused why the std::move(std::string) not making the passed std::string argument to an empty state (I mean std::string size as 0 and its internal buffer to point to nullptr after call to std::move(std::string)). This is a sample code

#include <iostream>
#include <string>

void print(std::string& str) {
    std::cout << "lref\n";
    std::cout << str << "\n" << std::endl;
}

void print(const std::string& str) {
    std::cout << "const lref\n";
    std::cout << str << "\n" << std::endl;
}

void print(std::string&& str) {
    std::cout << "rref\n";
    std::cout << str << "\n" << std::endl;
}

int main() {
    std::string str_a = "Hello, ";
    std::string str_b = "world!";
    
    print(str_a);
    print(str_b);
    print(str_a + str_b);
    
    print(std::move(str_a));
    print(str_a); // was expecting str_a to be empty but still prints Hello, 
    
    return 0;
}

Upvotes: 2

Views: 767

Answers (1)

alex_noname
alex_noname

Reputation: 32233

std::move is not moving anything. It cast its argument to an rvalue-reference. To actually move you need to pass str as rvalue-reference to move constructor(or move assignment) of another string as below.

std::string new_str(std::move(str));
print(str);

Upvotes: 5

Related Questions