Detailed explanation of C++ function calls: in-depth analysis of parameter passing mechanism

C Function calls have three parameter passing mechanisms: call by value (copy parameter value), call by reference (pass parameter reference, the original variable can be modified), and pointer pass (pass parameter pointer). The selection mechanism needs to consider parameter size, whether the original variables need to be modified, and efficiency.

C Detailed explanation of function calling: In-depth analysis of parameter passing mechanism

In C, function calling involves passing parameters from the caller to the called function. The parameter passing mechanism determines how the called function receives and uses these parameters. There are three main parameter passing mechanisms:

Call by value

• In a call by value, the parameter value is copied into the function.
• The original variable is not affected by any modifications in the function.
• It is very efficient for small data types (such as int, float), but less efficient for large data types (such as arrays).

Sample code:

void swap(int a, int b) {
  int temp = a;
  a = b;
  b = temp;
}

int main() {
  int x = 10;
  int y = 20;
  swap(x, y);
  cout << "x: " << x << ", y: " << y << endl; // 输出：x: 10, y: 20
}

Call by reference

• In the call by reference, parameters References are passed into functions rather than parameter values.
• Function can modify the original variable.
• Calling by reference is more efficient than calling by value.

Sample code:

void swap(int& a, int& b) {
  int temp = a;
  a = b;
  b = temp;
}

int main() {
  int x = 10;
  int y = 20;
  swap(x, y);
  cout << "x: " << x << ", y: " << y << endl; // 输出：x: 20, y: 10
}

Pointer passing

• In pointer passing, the parameter pointer is Neither parameter values ​​nor parameter references are passed into the function.
• Function can modify the original variable or pointer.

Sample code:

void swap(int* p, int* q) {
  int temp = *p;
  *p = *q;
  *q = temp;
}

int main() {
  int x = 10;
  int y = 20;
  swap(&x, &y);
  cout << "x: " << x << ", y: " << y << endl; // 输出：x: 20, y: 10
}

Choose the appropriate parameter passing mechanism

Choose the appropriate parameter passing mechanism depends Depends on the following factors:

• The size and type of parameters
• Whether the original variables need to be modified
• Efficiency considerations

In general , for values ​​that are small and do not need to be modified, you can use call-by-value. For values ​​that need to be modified, you can use call-by-reference or pointer passing. For large data types, pointer passing is usually the best choice.

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