C++ function call performance tuning: impact of parameter passing and return values

C function call performance optimization includes two aspects: parameter passing strategy and return value type optimization. In terms of parameter passing, passing values ​​is suitable for small objects and unmodifiable parameters, while passing references or pointers is suitable for large objects and modifiable parameters, and passing pointers is the fastest. In terms of return value optimization, small values ​​can be returned directly, and large objects should return references or pointers. Choosing the appropriate strategy can improve function call performance.

C Function call performance tuning: The impact of parameter passing and return value

In C, function calls will bring There is a certain performance overhead. The speed of function calls can be affected by parameter passing and return value types.

Parameter passing strategy

There are three parameter passing strategies in C:

1. Pass-by-value : The copy value is passed to the function, and any modification to the passed parameters will not affect the original value. This is a simple but slower way, especially when passing large objects.
2. Pass-by-reference: The function receives a reference to the original value, and modifications within the function will affect the original value. Faster, but requires ensuring variable lifetime throughout the function call.
3. Pass-by-pointer: Similar to passing a reference, the function receives a pointer to the original value. The fastest, but you need to pay attention to the dangling pointer.

Selecting the best strategy

Selecting the best parameter passing strategy depends on the following factors:

• Parameter size :Large objects should be passed by reference or pointer.
• Parameter modifiability: Functions that need to modify parameters should pass a reference or pointer.
• Portability: Passing by reference may have cross-platform compatibility issues.

Example:

The following code snippet compares the difference between passing a value and passing a pointer:

#include <iostream>

int calculate_cube(int value) {  // 传递值
  return value * value * value;
}

int calculate_cube_ptr(int *value) {  // 传递指针
  return *value * *value * *value;
}

int main() {
  int number = 5;
  std::cout << "Value: " << number << "\n";
  int result_value = calculate_cube(number);  // 传递值
  std::cout << "Result_value: " << result_value << "\n";

  std::cout << "Value: " << number << "\n";
  int result_ptr = calculate_cube_ptr(&number);  // 传递指针
  std::cout << "Result_ptr: " << result_ptr << "\n";
}

Run the program and output the results As follows:

Value: 5
Result_value: 125  // number 值未改变
Value: 5
Result_ptr: 125  // number 值已更改

Return value optimization

The return value type can also affect the performance of function calls. Small values ​​can be returned as values, while large objects should be returned as references or pointers.

Example:

The following code snippet compares the impact of the return value:

#include <iostream>
#include <vector>

struct LargeObject {
  int data[100];
};

LargeObject create_object() {  // 返回对象
  LargeObject object;
  return object;
}

LargeObject *create_object_ptr() {  // 返回指针
  LargeObject *object = new LargeObject();
  return object;
}

int main() {
  LargeObject object1 = create_object();  // 返回值
  LargeObject *object2 = create_object_ptr();  // 返回指针
}

Run the program and the output will be as follows:

[Higher runtime and memory usage due to object copy vs. pointer allocation]

Conclusion

The performance of function calls in C can be significantly improved by careful choice of parameter passing and return value types. Understanding the trade-offs of different strategies is critical to effective performance tuning.

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