指针复习

int *fun()
{
    int a = 10;
    return &a;  //函数调用完毕，a释放
}
int main(int argc,char *argv[]) {
   
    int* p = NULL;
    p = fun();
    *p = 100;  //操作野指针指向的内存，容易报错
   
    system("pause");
    return 0;
}

int *fun()
{
    static int a = 10; //函数调用完毕，a不释放
    return &a;
}
int main(int argc,char *argv[]) {
    int* p = NULL;
    p = fun();
    *p = 100;
    printf("p=%d\n", *p);
   
    system("pause");
    return 0;
}

void fun(int *tmp)
{
    tmp = (int *)malloc(sizeof(int));//堆区分配空间，将地址传递给tmp
    *tmp = 100;//将堆区的地址里面的值修改为100
}
int main(int argc,char *argv[]) {
    int* p = NULL;
    fun(p);//值传递，形参修改不会影响实参
    printf("p=%d\n",*p);//err，操作空指针指向的内存
   
    system("pause");
    return 0;
}
void fun(int *tmp)
{
       *tmp = 100;
}
int main(int argc,char *argv[]) {
    int* p = NULL;
    p = (int*)malloc(sizeof(int));
    fun(p);//值传递
    printf("p=%d\n",*p);//成功打印
   
    system("pause");
    return 0;
}

void *fun()
{
    int* tmp = NULL;
    tmp = (int*)malloc(sizeof(int));
    *tmp = 100;
    return tmp;//返回堆区地址，函数调用完毕，不释放
}
int main(int argc,char *argv[]) {
   int* p = NULL;
   p=fun();//值传递
    printf("p=%d\n",*p);
    if (p != NULL)
    {
        free(p);
        p = NULL;
    }
   
    system("pause");
    return 0;
}

void fun(int **tmp)
{
    *tmp = (int*)malloc(sizeof(int));
    **tmp = 100;
}
int main(int argc,char *argv[]) {
    int* p = NULL;
    fun(&p);
    printf("*p=%d\n", *p);
   
    system("pause");
    return 0;
}