Detailed explanation of the passing methods of C++ function parameters: passing by value and passing by reference

C Parameter passing methods are divided into value passing and reference passing. Passing by value creates a copy of the function parameters without affecting the original variables; passing by reference directly operates the original variables. The choice depends on your needs: protect the original variable using pass by value, modify the original variable or improve efficiency using pass by reference.

#C Detailed explanation of the passing methods of function parameters: value passing and reference passing

In C, function parameters can be passed in two ways Methods of passing: passing by value and passing by reference. Understanding the difference between these two passing methods is crucial because it affects the behavior of the function and the arguments passed.

Pass by value

In pass by value, a copy of the function parameters is passed to the function. This means that any changes passed into the function will not be reflected in the original variables passed in the calling function.

Advantages:

• Protect original variables from accidental modification
• Easy to reason about function behavior

Example:

void printValue(int x) {
  x *= 2;  // 修改副本
}

int main() {
  int a = 5;
  printValue(a);  // 传递 a 的副本
  std::cout << a << std::endl;  // 输出 5，表明原始变量没有被修改
}

Pass by reference

In pass by reference, the reference of the parameter is passed to the function. This means that any changes made to the parameters passed into the function will be reflected in the original variables passed in the calling function.

Advantages:

• Reduce data copies and improve efficiency
• You can modify the original variables in the calling function

Example:

void printAndDoubleValue(int& x) {
  std::cout << x << std::endl;  // 输出原始变量
  x *= 2;  // 修改原始变量
}

int main() {
  int a = 5;
  printAndDoubleValue(a);  // 传递 a 的引用
  std::cout << a << std::endl;  // 输出 10，表明原始变量被修改为副本的两倍
}

Which delivery method to choose?

The choice of passing method depends on the specific situation:

• Use passing by value if you need to protect the original variable or avoid unnecessary copies.
• If you need to modify the original variables in the calling function or improve efficiency, please use reference passing.

Practical case

Suppose we have a function that needs to change the case of the input string. We can use pass by value to ensure that the input string is not modified, or pass by reference to directly modify the original string:

// 值传递（输入字符串保持不变）
void printLowercase(const std::string& input) {
  std::cout << input.toLower() << std::endl;
}

// 引用传递（修改原始字符串）
void printUppercase(std::string& input) {
  input.toUpper();
}

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