RVO or `std::move` for Return Values in C : When Should I Use Which?

Return Value Optimization or Move?

In C , when returning a value from a function, there are two primary approaches: using Return Value Optimization (RVO) or explicitly using the std::move function. This question explores when to employ each method, using a specific example as a case study.

Example:

Consider the following code snippet that reads data into a SerialBuffer object and returns it:

SerialBuffer read(size_t size) const
{
    SerialBuffer buffer(size);
    read(begin(buffer), end(buffer));

    // Use RVO (first method)
    return buffer;

    // Explicit move (second method)
    // return std::move(buffer);
}

Use RVO:

According to the provided answer, in most cases, it is recommended to use RVO (the first method). RVO allows the compiler to automatically transform what would be a copy operation into a move operation if possible. This optimization can significantly improve performance, especially for large objects. In the example above, the compiler may recognize that the SerialBuffer object can be moved directly into the return statement, eliminating the need for a copy.

Prohibit RVO:

The second method, using std::move, explicitly prevents RVO. This is useful in specific scenarios where RVO is not desired. For instance, if the SerialBuffer class contains shared data or performs cleanup operations in its destructor, using std::move ensures that a proper copy is made instead of a move.

Conclusion:

In general, it is preferable to rely on RVO for return values. The compiler can efficiently determine when to perform a move, resulting in improved performance without the need for explicit coding. In exceptional cases where RVO is not suitable, using std::move can be considered. However, it is important to understand the implications of disabling RVO and handle the object's lifetime accordingly.

The above is the detailed content of RVO or `std::move` for Return Values in C : When Should I Use Which?. For more information, please follow other related articles on the PHP Chinese website!