What are the pointer parameters in the parentheses of the C language function?

The pointer parameters of C language function directly operate the memory area passed by the caller, including pointers to integers, strings, or structures. When using pointer parameters, you need to be careful to modify the memory pointed to by the pointer to avoid errors or memory problems. For double pointers to strings, modifying the pointer itself will lead to pointing to new strings, and memory management needs to be paid attention to. When handling pointer parameters to structures or arrays, you need to carefully check the pointer type and boundaries to avoid out-of-bounds access.

The secret of those pointer parameters in parentheses of C language function

You ask about the pointer parameters in parentheses of C functions? This question is well asked! On the surface, it's just a pointer, but behind it is the essence of C language, which can even make you play with performance optimization and code elegance. In this article, let’s take a look at the details of these pointer parameters, and then talk about the pitfalls I have struck by writing C code over the years, as well as some unique tips to avoid these pitfalls.

First of all, it should be clear that pointer is not a monster in C, it is just a memory address. The pointer in the function parameter means that the function can directly operate the memory area passed in by the caller. This is both its power and its prone to errors.

Let's start with the simplest: int *ptr . This represents a pointer to an integer. When it appears as a function parameter, any modifications to ptr within the function will be directly reflected in the memory provided by the caller. This is completely different from the value-passing parameter. The value-passing parameter is just a copy of it to the function.

 <code class="c">void modify_int(int *ptr) { *ptr = 10; // 直接修改ptr指向的内存的值} int main() { int x = 5; modify_int(&x); // 传递x的地址printf("%d\n", x); // 输出10 return 0; }</code>

Have you seen it? The modify_int function directly changes the value of x in the main function. This is the power of pointer parameters, and it is also the place where it is prone to errors. If you are not careful, you may modify memory that should not be modified, causing the program to crash or unpredictable errors. It's like holding a scalpel, you may accidentally scratch the place you shouldn't.

To be more complicated, consider char **ptr . This guy points to a pointer to a character, that is, a pointer to a string, which is usually used to process string arrays or string pointer arrays.

 <code class="c">void modify_string(char **ptr) { *ptr = "Hello, world!"; // 修改ptr指向的指针，指向新的字符串} int main() { char *str = "Original string"; modify_string(&str); printf("%s\n", str); // 输出"Hello, world!" // 注意：原字符串"Original string"可能在内存中被释放，这取决于你的内存管理策略。 return 0; }</code>

Here, the modify_string function modifies the str pointer itself so that it points to a new string. This is very useful when dealing with dynamically allocated strings, but also requires attention to memory leaks and dangling pointers. Remember, before modifying the pointer, be sure to make sure you fully understand the life cycle of the memory area it points to.

There is another case where the pointer parameter points to a structure or array. This is very common when dealing with complex data structures. At this time, you need to be extra careful about the type and bounds of the pointer, otherwise it will be easy to access over the bounds and cause the program to crash.

In short, the pointer parameters in C language functions are like a double-edged sword. If you use them well, you will get twice the result with half the effort. If you use them poorly, you will get into trouble. Understanding the nature of pointers, carefully checking the type and boundaries of pointers, and developing good coding habits are all the keys to avoiding pitfalls. Remember to be cautious, be cautious! Only in this way can you be at ease in the C world. Finally, practicing more and debugging more is the kingly way.

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