A brief analysis of the precautions for using C/C++ language structure pointers

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#include <>
#include <>
#include <>

typedef struct Staff_t{
    char* name;
    char sex;
    short age;
    float salary;
    char* date;
} STAFF_T;

void print_msg(STAFF_T const *p); // Example of using structure pointer as function parameters
int main()
{   
    int size;
    
    //STAFF_T sta; // Define a structure    //staff = &sta; // Another type of structure initialization    STAFF_T* staff = NULL; // Define a structure pointer and initialize it to NULL;
    // Apply for memory space for the structure, and casting is required (here is the structure pointer type). Note that malloc successfully returns the number of bytes, and returns NULL if it fails.    staff = (STAFF_T*)malloc(sizeof(STAFF_T)); 
    // Determine whether the application space is successful. Only when the application is successful can it be used. This step is very important and many people are prone to forget it.    if (staff == NULL)
    {
        printf("malloc(STAFF_T) ERROR\n");
        return -1;
    }

    // Here are a few lines of debugging, print out that the memory space occupied by some data types in the 32/64-bit system is different in size    size = sizeof(STAFF_T);
    printf("STAFF_T size = %d\n",size);
    printf("SIZEOF:\n char*:%lu, char:%lu,short:%lu,float:%lu \n",sizeof(char*),sizeof(char),sizeof(short),sizeof(float));

    staff->name = (char*)malloc(20*sizeof(char));
    
    // In C language, both assignment methods below staff->name are OK    staff->name = "duruofei";//strcpy(staff->name, "duruofei");
    staff->sex = 'M';
    staff->age = 29;
    staff->salary = 15000;
    staff->date = (char*)malloc(20*sizeof(char));
    strcpy(staff->date,"2021-12-09");//strcpy(staff->date, "2021-12-09");
    
    // Pass the structure pointer    print_msg(staff); // The parameter is a pointer constant, because here it is just reading the value of staff, and you do not want to modify the content of staff
    // Finally release the pointer and assign it to NULL.  Because the memory address pointed to by the pointer after the pointer is free can be used by other variables, but the pointer itself still points to the original address and can also be used to prevent wild pointers from being    free(staff);
    staff = NULL;

    printf("Hello World\n");

    return 0;
}

/**
 * function: print_msg
 * input: STAFF_T const *
 * ouput: none
 * descreption: print massage
 */
void print_msg(STAFF_T const *p)
{
    // The parameter is a pointer constant, because here it is just reading the value of p, and you do not want to modify the content of p    if (p == NULL) 
    {
        printf("print_msg: p is NULL\n");
    }
    
    printf("Name:%s, Sex:%c, Age:%d, Salary:%0.2f, Date:%s\n",\
            p->name, p->sex, p->age, p->salary, p->date);
}