structures and pointers

Question

#include<stdio.h>
struct game{
    int level;
    int score;
    struct player{
        char *name;
    } g2;
} g1;

int main(){
    printf("%d %d %s",g1.level,g1.score,g1.g2.name);
}

 

What will output when you compile and run the above code?

(a) Garbage_value garbage_value garbage_value

(b) 0 0 (null)

(c) Run time error

(d) Compiler error

can anyone tell me whats th answer??

and shoul'nt it give the error for g1.g2.name because name is a charcter pointer we are trying to access it before giving it some memory or initializing it with a value..??(as before accessing pointers,you should initialize them as far as i know,otherwise we get an error)

Comments

0 0 (null)

Answer 1

Any global/static variable in C is initialized to 0. So, output will be

0 0

For the final one, we are giving name the value 0 and printing it as string. So, this is like printing th string from address 0, which should cause undefined behaviour - can even crash and give segmentation fault.

If we move the structure definition to be inside main as shown below, then the first 2 values are garbage and 3rd one might cause access to invalid memory location depending on the garbage value pointed to by name.

    #include<stdio.h>
    int main(){
        struct game{
        int level;
        int score;
        struct player{
            char *name;
        } g2;
    } g1;
        printf("%d %d %s",g1.level,g1.score,g1.g2.name);
    }

Comments

@Arjun

in this question, $\color{red}{\text{name}}$ is a global character pointer ==> initialized to memory location 0.

sir, i have a doubt that

Normally OS present in the DISK( Non-volatile memory ), When we power on the computer, BIOS will load the OS in to the RAM ( which is volatile but faster than Disk ).

Now what i am thinking is $\color{blue}{\text{'' Exactly Where in the RAM, the OS is loaded ?}  \\ \text{( i mean to ask from which memory location, OS is loaded? ) "}}$

i am thinking it is  " always at memory location 0 to some value, OS present " --- if this is the case then accessing the location which is pointed by $\color{red}{\text{name}}$ pointer should be always lead to segmentation fault ===> abnormal termination ===> run time error !

if OS, is not loaded at memory location 0, then we can load a process at memory location 0?

if any process can load at 0, then by coincide this program may authorize to access the location 0, right?

and i also have a conceptual doubt that, " we have to recognize all the global variables at compile time "

is we assign a memory address to them at compile time ? i hope yes, but it is relative address but not absolute address, right ?

---

I don't think it is "0" but must be a fixed location. Also in a VM system, only the VA matters for the OS or CPU.

Address for global variables - yes, they are relative with respect to the program load address.

---

ok, sir, thank you !