C language entry pointer summary

Several Right and Wrong Ways of Pointer in C Language

Error 1,

void Swap(int a, int b)//未传指针
{
    
    
 int tmp = a;
 a = b;
 b = tmp;
}

In this way, in the code that calls the function to exchange, it can be seen that it is only a simple exchange of the respective stored addresses. No pointer is passed!

Error 2,

void Swap(int* p1, int* p2)//未解引用
{
    
    
 int* tmp = p1;
 p1 = p2;
 p2 = tmp;
}

Although the addresses of a and b are passed in in this way, the corresponding addresses are not operated. No dereference!

Error 3.

void Swap(int* p1, int* p2)//有野指针 tmp的值未初始化
{
    
    
 int* tmp;
 *tmp = *p1;
 *p1 = *p2;
 *p2 = *tmp;
}

This method uses pointer transfer and dereference, but the value of tmp is not initialized!

The right way

void Swap(int* p1, int* p2)
{
    
    
 int tmp;
 tmp = *p1;
 *p1 = *p2;
 *p2 = tmp;
}

to sum up

1. If a function wants to modify the value of another function, it must pass pointers and dereference.
2. Wild pointers and dangling pointers: addresses without access rights.
3. Null pointers (NULL): the current pointer is invalid