Callback

In computer science, a callback is a concept, which allow a low level layer to call a function from a higher level layer, when usually, the higher level call the low level layer.

C Example

Here is an example in the C programming language

void counter( void (*cb)(int) )
{
   int i;
   for (i=15; i<20;i++)
   {
       cb(i);
   }
}
/** print number in hexadecimal */
void printHex(int i)
{
   printf("%x\\n",i);
}

/** print number in decimal */
void printDec(int i)
{
   printf("%d\\n",i);
}

int main(void)
{
   void (*fn)(int);
   printf ("decimal:\\n")
   fn = &printDec;
   counter(fn);
   printf ("hexa:\\n")
   fn = &printHex;
   counter(fn);

   return 0
}

Example result

decimal:
15
16
17
18
19
hexa:
f
10
11
12
13
14