Lære Move Constructors | Implementing Move Operations

A move constructor enables an object to take ownership of resources from a temporary (rvalue) object, avoiding expensive deep copies. Its signature uses an rvalue reference.

main.cpp


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#include <iostream>
#include <cstring>

class StringHolder {
public:
    char* data;

    // Constructor
    StringHolder(const char* str)
    {
        data = new char[std::strlen(str) + 1];
        std::strcpy(data, str);
        std::cout << "Constructed: " << data << std::endl;
    }

    // Move constructor
    StringHolder(StringHolder&& other) noexcept
    {
        data = other.data;
        other.data = nullptr;
        std::cout << "Move constructed." << std::endl;
    }

    // Destructor
    ~StringHolder()
    {
        if (data)
            std::cout << "Destroyed: " << data << std::endl;
            delete[] data;
        else
            std::cout << "Destroyed: nullptr" << std::endl;
    }
};

int main()
{
    StringHolder a("hello");
    StringHolder b(std::move(a));
}

In the example above, the move constructor transfers the resource pointer and nulls out the source, ensuring only one object manages the resource.

A move constructor is called when an object is initialized from a temporary (rvalue) of the same type, such as when returning a local object from a function or using std::move.

After the move, the source object should be left in a valid but unspecified state. Typically, pointers are set to nullptr.

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