Quick introduction to reverse engineering for beginners

1.18 Pointers to functions
Pointer to function, as any other pointer, is just an address of function beginning in its code segment.
It is often used in callbacks 62 .
Well-known examples are:
∙ qsort() 63 , atexit() 64 from the standard C library;
∙ signals in *NIX OS 65 ;
∙ thread starting: CreateThread() (win32), pthread_create() (POSIX);
∙ a lot of win32 functions, for example EnumChildWindows() 66 .
So, qsort() function is a C/C++ standard library quicksort implemenation. The functions is able to
sort anything, any types of data, if you have a function for two elements comparison and qsort() is able to
call it.
The comparison function can be defined as:
int (*compare)(const void *, const void *)
Let’s use slightly modified example I found here:
/* ex3 Sorting ints with qsort */
#include
#include
int comp(const void * _a, const void * _b)
{
const int *a=(const int *)_a;
const int *b=(const int *)_b;
}
if (*a==*b)
return 0;
else
if (*a < *b)
return -1;
else
return 1;
int main(int argc, char* argv[])
{
int numbers[10]={1892,45,200,-98,4087,5,-12345,1087,88,-100000};
int i;
}
/* Sort the array */
qsort(numbers,10,sizeof(int),comp) ;
for (i=0;i