C++ function return values: types and meanings

C The function returns a value through the return statement. The type and meaning are as follows: Return value type: Specify the data type returned by the function, including basic types, special types (such as void, auto, reference, enumeration), etc. The meaning of the return value: depends on the purpose of the function, common meanings are: error code calculation result object reference Boolean value

C Complete list of function return values: types and meanings

In C, a function can return a value through the return statement. The type and meaning of function return values ​​are important to understanding the code.

Return value type

The return value type of a function can be specified in the function declaration, as follows:

int add(int a, int b);

This declaration indicates that The add function will return a int type value.

Special return value types

In addition to basic data types, C also has the following special return value types:

• void : Indicates that the function does not return any value.
• auto: Let the compiler automatically infer the return value type.
• Smart pointer: A pointer to a dynamically allocated object.
• Reference: Alias ​​pointing to other variables or objects.
• Enumeration type: A custom type that represents a set of predefined constants.

The meaning of the return value

The meaning of the function return value depends on the purpose of the function. Here are some examples of common meanings:

• Error Code: Indicates success or failure of the operation.
• Calculation results: Contains the results of function calculations.
• Object reference: Returns a pointer to an object instance.
• Boolean value: Indicates that the condition is true or false.

Practical case

The following code example shows function return values ​​with different meanings:

// 返回错误代码
int openFile(const char* filename) {
  FILE* file = fopen(filename, "r");
  if (!file) {
    return -1; // 文件打开失败
  }
  return 0; // 文件打开成功
}

// 返回计算结果
int calculateArea(int length, int width) {
  return length * width;
}

// 返回对象引用
Person* createPerson(const char* name, int age) {
  return new Person(name, age);
}

void main() {
  int openResult = openFile("test.txt");
  if (openResult == -1) {
    std::cerr << "文件打开失败\n";
  }
  else {
    std::cout << "文件打开成功\n";
  }

  int area = calculateArea(5, 10);
  std::cout << "面积为：" << area << "\n";

  Person* person = createPerson("John Doe", 30);
  std::cout << "姓名：" << person->name << ", 年龄：" << person->age << "\n";

  // 释放动态分配的内存
  delete person;
}

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