Lära Why Copying Isn’t Always Efficient | Introduction to Move Semantics

Copying objects in C++ can be expensive, especially when dealing with large resources such as dynamically allocated memory or containers. Each copy operation may involve allocating new memory and duplicating the contents, which can significantly impact performance.

main.cpp


              1234567891011121314151617181920212223242526272829303132333435363738394041
            
#include <iostream>
#include <cstring>

class LargeBuffer {
public:
    LargeBuffer(size_t size)
        : size_(size), data_(new char[size]) {
        std::cout << "Constructed LargeBuffer of size " << size_ << std::endl;
        std::memset(data_, 0, size_);
    }

    // Expensive copy constructor
    LargeBuffer(const LargeBuffer& other)
        : size_(other.size_), data_(new char[other.size_]) {
        std::cout << "Copied LargeBuffer of size " << size_ << std::endl;
        std::memcpy(data_, other.data_, size_);
    }

    // Destructor
    ~LargeBuffer() {
        std::cout << "Destroyed LargeBuffer of size " << size_ << std::endl;
        delete[] data_;
    }

    size_t size() const { return size_; }

private:
    size_t size_;
    char* data_;
};

void processBuffer(LargeBuffer buf)
{
    std::cout << "Processing buffer of size " << buf.size() << std::endl;
}

int main()
{
    LargeBuffer buf1(1024 * 1024); // 1 MB buffer
    processBuffer(buf1); // Copies buf1 into the function
}

In the example above, notice how copying the object leads to additional memory allocations and data duplication. This inefficiency becomes more pronounced as the size of the resource grows.

Copying is necessary when you need two independent objects with the same state. For example, when you want to preserve the original while modifying the copy.

Move semantics allow you to transfer resources instead of duplicating them, which is especially useful for temporary objects or when ownership can be transferred.

Var allt tydligt?

Tack för dina kommentarer!

Avsnitt 1. Kapitel 1

Fråga AI

Fråga vad du vill eller prova någon av de föreslagna frågorna för att starta vårt samtal

Svep för att visa menyn