在c / c ++中混淆指向结构的指针

Question

I'm trying to remove some confusion with pointer to structures which are used as members in class. I wrote following code, but even though the program compiles it crashes. Could you please say what I'm doing wrong in the following code?

#include<stdio.h>
#include<string.h>

struct a{
    int s;
    int b;
    char*h;
};

class test
{
public:
    a * f;
    void dh();
    void dt();
};

void test::dh()
{
    a d;
    d.s=1;
    d.b=2;
    d.h="ffdf";
    f=&d;
}

void test::dt()
{
    printf("%s %d %d",f->h,f->b,f->s);
}

int main()
{
    test g;
    g.dh();
    g.dt();
    return 0;
}

Answer 1

void test::dh()
{
    a d; <--
    d.s=1;
    d.b=2;
    d.h="ffdf";
    f=&d; <--
}

You're creating a local object, d , and then setting f to the address of this object. Once the function ends, the object goes out of scope and you're left with a dangling pointer.

Answer 2

Your biggest problem is that by the time dh() returns, d is no longer in scope. Instead of ad; in dh() , you need f = new a(); fs=1; fb=2, fh="ffdf"; f = new a(); fs=1; fb=2, fh="ffdf"; .

Answer 3

In test::dh, you assign public pointer f the address of d, which is a local variable. When g.dh(); exits, the address of d is no longer valid, which is why the references to f in g.dt(); fail.