How to use int point to struct in c

Question

i use int8_t* to point the struct,and i can use cout to print the "num" data, but how to print the "b" data?

here is my code

struct A_T{
    int num;
    char *b;
};
int main()
{
    A_T *a=new A_T();
    a->num=10;
    a->b="aaa";
    int8_t *p;
    p=(int8_t*)a;
    cout<<a->num<<endl;
    cout<<*p<<endl;
    return 0;
}

cout<<*p<<endl can print the "num" data is 10, but when i use cout<<*(p+1)<<endl to print "b" data, it prints nothing.

can you help me ?

thank you

Why? Why not just use `a` to print the struct. In any case you probably need to investigate the `offsetof` macro. — john, Jun 30 '20 at 06:28
@tianyu Then change those methods so they don't use integer pointers. — john, Jun 30 '20 at 06:34
@tianyu john's answer is good and if you want to know why `*p` doesn't seem to print anything: https://stackoverflow.com/questions/7587782/why-is-stdcout-not-printing-the-correct-value-for-my-int8-t-number — Lukas-T, Jun 30 '20 at 06:37
Instead of `a->num = 10;` try `a->num = 3000;`. You'll see that `std::cout << *p` **doesn't** print the value of `num`. — Pete Becker, Jun 30 '20 at 13:46

score 4 · Answer 1 · answered Jun 30 '20 at 06:34

4

It's painful but this might work for you

#include <stddef.h>

cout << *(char**)(p + offsetof(A_T, b)) << '\n';

answered Jun 30 '20 at 06:34

john

85,011
4
57
81

score 1 · Accepted Answer · answered Jun 30 '20 at 06:38

1

You could use from this 'cout << ((A_T *)p)->b<<endl;' instraction inorderto access member b of struct.

answered Jun 30 '20 at 06:38

Farhad Sarvari

1,051
7
13

How to use int point to struct in c

2 Answers2