Performance comparison of lvalue and rvalue parameter passing in C++ functions

Performance difference between lvalue and rvalue parameter passing. Lvalue parameter passing has copy overhead and reduces performance, especially for large objects. Rvalue parameter passing avoids copy overhead and improves performance, especially for temporary objects or literals.

C Performance comparison of lvalue and rvalue parameter passing

In C, function parameter passing can use lvalue Or rvalue way. An lvalue reference (lvalue parameter) represents a reference to an existing object, while an rvalue reference (rvalue parameter) represents a reference to a temporary object or literal.

Performance impact

For lvalue parameters, a copy of the actual parameter will be passed to the function when the function is called. This involves the overhead of making copies, which may reduce performance, especially for large objects.

Rvalue parameters, on the other hand, avoid making copies and instead pass the actual parameters themselves to the function. This eliminates copy overhead and improves performance, especially when dealing with temporary objects or literals.

Practical case

The following code demonstrates the performance difference between lvalue and rvalue parameter passing:

#include <iostream>

// 左值参数函数
void left_value_func(int& lvalue) {
  lvalue++;
}

// 右值参数函数
void right_value_func(int&& rvalue) {
  rvalue++;
}

int main() {
  // 左值参数
  int lvalue = 10;

  // 右值参数
  int rvalue = 20;

  left_value_func(lvalue);  // 调用左值参数函数
  right_value_func(rvalue);  // 调用右值参数函数

  std::cout << "左值参数: " << lvalue << std::endl;
  std::cout << "右值参数: " << rvalue << std::endl;

  return 0;
}

Output:

左值参数: 11
右值参数: 21

In this example, the lvalue argument passes a copy of an existing variable, while the rvalue argument passes the temporary variable itself. It turns out that rvalue parameter function calls are faster because the overhead of making copies is avoided.

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