Doubt in pointer to structure

Code:

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static int *p;

void main()
{
    point_update(&p);
    printf("%d",*p);
}

point_update(int **q)
{
  int x = 5;
  *q = &x;
}

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In the above pgm, why *p is giving some junk value?

When control returns from the point_update function, the local variable x no longer exists, hence dereferencing p in main leads to undefined behaviour. Also, to print a pointer, you should be using the %p format specifier, not %d, and you should cast the pointer argument to void*. Oh, and void main should be int main, and you should declare point_update before using it.

In addition to all that laserlight has said, specify the return type of point_update() as well.

Quote:

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Originally Posted by grumpy

In addition to all that laserlight has said, specify the return type of point_update() as well.

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The default return type of a function is int,but it is better to declare it by yourself.
In this case,you should declare it void of course :)

In addition to allthat grumpy and laserlight and std10093 said, you need to have a prototype declared before you call a function that takes a variable number of parameters. In this case, the prototype for the function printf() is in the standard header <stdio.h>

Code:

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#include <stdio.h>
/* ... */

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Quote:

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Originally Posted by std10093

The default return type of a function is int,but it is better to declare it by yourself.
In this case,you should declare it void of course :)

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Actually that is only true with the outdated C standards, like C89-90. The current standard doesn't allow default return types.

Jim

Quote:

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Originally Posted by qny

In addition to allthat grumpy and laserlight and std10093 said, you need to have a prototype declared before you call a function that takes a variable number of parameters. In this case, the prototype for the function printf() is in the standard header <stdio.h>

Code:

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#include <stdio.h>
/* ... */

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Or instead of a prototype,you could define your function before you use it (before main in other words) :)
definition

Code:

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int foo(void)
{
    printf("inside foo\n");
}

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declaration

Code:

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int foo(void);

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The way that gny is more elegant and it is the one i suggest