Access function pointer defined in a structure?

Question

Write a program to access the function "foo" using the structure structure2.

typedef struct
{
   int *a;
   char (*fptr)(char*);
}structure1;

typedef struct
{
   int x;
   structure1 *ptr;
}structure2;

char foo(char * c)
{
---
---
---
}

Answer 1

• Create an object of type structure2
• Assign to it the address of an object of type structure1 (this can be done in quite a few ways)
• Assign foo to the above allocated structure1 object's fptr member

• Call foo using:

  structure2 s2;
  // allocate 
  char c = 42;
  s2.ptr->fptr(&c);  // if this
  

Example:

typedef struct
{
   int *a;
   char (*fptr)(char*);
}structure1;

typedef struct
{
   int x;
   structure1 *ptr;
}structure2;

char foo(char * c)
{
return 'c';
}

int main()
{
 structure1 s1;
 structure2 s2;
 s1.fptr = foo;
 s2.ptr = &s1; 
 char c = 'c';
 printf("%c\n", s2.ptr->fptr(&c));
return 0;
}

Answer 2

structure2 *s2 = (structure2*)malloc(sizeof(structure2));
s2->ptr = (structure1*)malloc(sizeof(structure1));
s2->ptr->fptr = foo;
char x = 'a';
s2->ptr->fptr(&x);