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Tip of the Day
Language:
Expertise: Beginner
Feb 21, 2002

Using Pointers as Integers


In the early days of C, pointers were plain integers. Relics of this approach can still be found in vintage APIs and legacy code. For instance, the ANSI C <signal.h> header declares the following typedef name:
 
typedef void(*handler)(int signum);

handler is a pointer to a function that takes int and returns void. It is used as the second parameter of the signal() function:
 
void * signal(int signum, hanlder); // from <signal.h>

Normally, handler points to a user-defined function to be called when a certain signal is raised. However, it may also take two special values: SIG_IGN and SIG_DFL which are in fact integer values (both are defined in <signal.h>). Thus, the pointer handler can represent either a real pointer or a numeric value. This "cuteness" isn
Danny Kalev
 
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