What is the difference between C++ function declaration and definition?

The function declaration informs the compiler of the existence of the function, does not contain implementation, and is used for type checking. The function definition provides the actual implementation, including the function body. Key distinguishing features include: purpose, location, role. Understanding the differences is critical to writing efficient and maintainable C code.

C Function declaration and definition: difference and practice

In C, function declaration and definition are two key concepts, Play different roles in program development. Understanding the difference between them is important to writing efficient and maintainable code.

Function declaration

A function declaration tells the compiler that the function exists, but it does not contain the actual implementation of the function. It specifies the function's name, parameter list, and return type. For example:

// 函数声明
int add(int a, int b);

A function declaration allows the compiler to type-check a function call even if it has not been defined yet.

Function definition

Function definition provides the actual implementation of the function. It contains the function body, which contains the actual logic of the function. For example:

// 函数定义
int add(int a, int b) {
  return a + b;
}

Function declarations and definitions can be separated in different files in the source code. This is called a function prototype.

Practical case

Consider a program that calculates the area of ​​a circle. We can calculate the area using a function as follows:

// 函数声明
double calculateArea(double radius);

// 函数定义
double calculateArea(double radius) {
  return 3.14159 * radius * radius;
}

In this example, the calculateArea function is declared to accept a parameter of type double and return a result of type double. Function definitions provide the actual calculation logic.

Summary of differences

#By understanding the difference between function declaration and definition, you can write more efficient C code and improve the readability and maintainability of your code .

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