A brief list of definitions and calls of c language functions

The C language function definition includes the specified return value type, function name, parameter list and function body. To call a function, just add the parameter with the function name. Parameter passing is passed by value by default, except pointer parameters. Function prototype declares function information to improve readability. Recursive function calls itself and requires a termination condition. Performance optimization can reduce function call overhead using inline functions or macro definitions.

C language functions: definitions and calls, details that you may not know

Many beginners think that the definition and call of C functions are simple, aren’t it just int func(int a){...} and func(5); ;? That's right, it's the case, but the devil is hidden in the details. In this article, let’s dig deeper and take a look at the unknown "secrets" of C language functions. After reading it, you will not only be able to master function definitions and calls, but also to a higher level in performance optimization and code elegance.

Let’s start with the most basic ones. A C function is essentially a reusable block of code. It receives input (parameter), processes it, and returns the result (return value). To define a function, you need to specify its return value type, function name, parameter list, and function body. For example:

 <code class="c">int add(int a, int b) { return ab; }</code>

This code defines a function called add that takes two integers a and b as input and returns their sum. Note that int means that the return value type is an integer. If no return value is used, use void .

Function calls are even simpler. Just use the function name and parameters, just like using a built-in function:

 <code class="c">int sum = add(5, 3); // 调用add函数，并将结果赋值给sum</code>

It looks simple, right? But things are much more than that.

The secret of parameter passing

The method of parameter passing determines whether the modification of parameters inside the function will affect variables outside the function. C language uses value passing, which means that the function receives a copy of the parameters, not the parameters themselves. Therefore, modifying the value of the parameter inside the function will not change the value of the external variable of the function.

 <code class="c">void modify(int x) { x = 10; // 修改局部变量x } int main() { int y = 5; modify(y); printf("%d\n", y); // 输出5，y的值没有改变return 0; }</code>

However, pointer parameters are an exception. The pointer passes a memory address, so the value of the original variable can be modified through the pointer inside the function.

 <code class="c">void modify_ptr(int *x) { *x = 10; // 修改x指向的内存中的值} int main() { int y = 5; modify_ptr(&y); printf("%d\n", y); // 输出10，y的值被改变了return 0; }</code>

Understanding pointer parameters is crucial to mastering C language and is also a place where many beginners are prone to make mistakes.

The importance of function prototypes

Before calling a function, the compiler needs to know the function's return value type and parameter list. This is what the function prototype does. A good programming habit is to declare function prototypes in header files, which can improve the readability and maintainability of the code and avoid many potential errors.

 <code class="c">// 在头文件中声明函数原型int add(int a, int b); // 在源文件中定义函数int add(int a, int b) { return ab; }</code>

Recursive functions

A recursive function refers to a function that calls itself within a function. Recursive functions are elegant and concise, but improper use can easily cause stack overflow. Make sure your recursive function has the correct terminating conditions and avoid infinite recursion.

 <code class="c">int factorial(int n) { if (n == 0) { return 1; // 终止条件} else { return n * factorial(n - 1); } }</code>

Performance optimization

Function calls will have some overhead, especially small functions that are frequently called. For programs with high performance requirements, you can consider using inline functions or macro definitions to reduce the overhead of function calls. But remember that inline functions and macro definitions also have some disadvantages, such as code bloating and potential debugging difficulties. Choosing the right optimization method requires weighing the pros and cons based on actual conditions.

In short, the definition and call of C functions seem simple, but they contain rich details and techniques. Only by mastering these details can you write more efficient and elegant C language code. Remember, programming is a practical art. Only by practicing more and thinking more can you become a real master of programming.

The above is the detailed content of A brief list of definitions and calls of c language functions. For more information, please follow other related articles on the PHP Chinese website!