Lære Move Semantics and std::move | Smart Pointers and Memory Management

Move semantics are a powerful feature in modern C++ that allow you to transfer resources from one object to another without unnecessary copying. This is achieved using rvalue references, which are a type of reference that can bind to temporary objects (also known as rvalues). The std::move utility is used to cast an object to an rvalue reference, signaling that the resources of the object can be moved rather than copied. This is especially useful for classes that manage dynamic memory or other resources, as it enables efficient transfer of ownership, avoiding redundant allocations and deallocations.

main.cpp


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#include <iostream>
#include <string>

int main()
{
    std::string original = "Hello, World!";
    std::string moved_to = std::move(original);

    std::cout << "moved_to: " << moved_to << std::endl;
    std::cout << "original (after move): " << original << std::endl;
}

While this simple example demonstrates moving a string, the real power of move semantics becomes clear when used in user-defined classes that manage dynamic resources. Implementing move constructors and move assignment operators can significantly improve performance by reusing existing allocations instead of duplicating them.

main.cpp


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#include <iostream>

class Buffer {
public:
    Buffer(size_t size) : size_(size), data_(new int[size]) {
        std::cout << "Allocated " << size_ << " ints\n";
    }

    // Move constructor
    Buffer(Buffer&& other) noexcept 
        : size_(other.size_), data_(other.data_) {
        other.data_ = nullptr; // Transfer ownership
        std::cout << "Moved buffer\n";
    }

    ~Buffer() { delete[] data_; }

private:
    size_t size_;
    int* data_;
};

int main()
{
    Buffer buf1(10);
    Buffer buf2 = std::move(buf1); // Move, not copy
}

This example shows how resources can be efficiently transferred using a move constructor. After the move, buf1 no longer owns its data, preventing double deletion while avoiding unnecessary copying.

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main.cpp


              1234567891011
            
#include <iostream>
#include <string>

int main()
{
    std::string original = "Hello, World!";
    std::string moved_to = std::move(original);

    std::cout << "moved_to: " << moved_to << std::endl;
    std::cout << "original (after move): " << original << std::endl;
}

main.cpp


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#include <iostream>

class Buffer {
public:
    Buffer(size_t size) : size_(size), data_(new int[size]) {
        std::cout << "Allocated " << size_ << " ints\n";
    }

    // Move constructor
    Buffer(Buffer&& other) noexcept 
        : size_(other.size_), data_(other.data_) {
        other.data_ = nullptr; // Transfer ownership
        std::cout << "Moved buffer\n";
    }

    ~Buffer() { delete[] data_; }

private:
    size_t size_;
    int* data_;
};

int main()
{
    Buffer buf1(10);
    Buffer buf2 = std::move(buf1); // Move, not copy
}

Var alt klart?

Tak for dine kommentarer!

Sektion 2. Kapitel 2