Detailed explanation of memset() function usage

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One 、memset The function prototype

void *memset(void *src, int value, size_t n);

here srs It can be array names , It can also be a pointer to a memory space ;
value For the values to be filled ;
n For the number of bytes to be filled , Usually it is sizeof(s);
Function functions ： Put the pointer variable src Front of the point n Byte memory unit with a “ Integers ” value Replace , Be careful value yes int type .src yes void* Pointer variable of type , So it can be initialized for any type of data .

Two 、 Use steps

1. Add header files and namespaces

The code is as follows （ Example ）：

#include <string.h>
using namespace std;

2. Array initialization

The code is as follows （ Example ）：

    char str[20];
    char *pt = str;
    memset(pt, 0, sizeof(str));  // take str The array is initialized to 0

3. Custom class initialization

In our custom class or structure , It usually defines int,char,double etc. Built in variable , Initialize them sentence by sentence in the constructor as 0 It seems very troublesome , So you can directly memset(this, 0, sizeof *this); Set the memory of the entire object to 0. It can work well in this situation , But the following situations can't be used like this ：

1. Class contains a table of virtual functions ： Will destroy the virtual function table , Exceptions will appear when calling virtual functions later ;
2. Class contains C++ Object of type ： for example , One is defined in the class vector The object of , Because before the code of the constructor body is executed vector Object is initialized , hypothesis vector It allocates memory in its constructor , So we're going to destroy it vector Object's memory .
The code is as follows （ Example ）：

	memset(this,0,sizeof(*this))