Detailed explanation of C++ function calls: The art of return value processing

C Return value processing in function calls involves: Return value type: Define the type of return data, including primitive types and reference types. Return value semantics: determines how the function handles return values, including passing by value (returning a copy) and passing by reference (returning a reference). Practical case: illustrates the usage scenarios and implementation methods of value passing and reference passing.

Detailed explanation of C function calls: The art of return value processing

Introduction

Function calls are the key to C programming The core concept of function return value is crucial to the correctness and efficiency of the program. This article will delve into the processing of function return values, covering return value types, return value semantics, and practical cases.

Return value type

The return value type of a function defines the type of data it returns. C supports a variety of return value types, including primitive types (such as int, float), class types, and void (meaning that the function returns no value).

Return value semantics

Return value semantics determine how a function handles its return value after it is called. There are two main return value semantics:

• Value passing: The function returns a copy of the returned value to the caller.
• Passing by reference: The function returns a reference pointing to the returned value, and the caller's manipulation of the reference will directly modify the returned value.

Value passing

By default, both function parameters and return values ​​are passed by value. This means that modifications to parameters or return values ​​inside a function do not affect external variables.

Passing by reference

Passing by reference can be achieved by using a reference as the return value type. Passing by reference is more efficient than passing by value because the caller does not need to create a copy of the returned value.

Practical Case

Case 1: Value Passing

int square(int x) {
  return x * x;
}

int main() {
  int y = square(5);
  cout << "y = " << y << endl; // 输出：y = 25
  return 0;
}

Case 2: Reference Passing

int& square(int& x) {
  x *= x;
  return x;
}

int main() {
  int z = 5;
  square(z); // z 被修改为 25
  cout << "z = " << z << endl; // 输出：z = 25
  return 0;
}

Conclusion

The correct handling of function return values ​​is crucial to ensuring the correctness and efficiency of the program. By understanding return value types and return value semantics, programmers can optimize their code and take full advantage of the power provided by the C language.

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