I need help trying to sort out a declaration for a system call to Linux but I'm not sure how to handle the situation where the function can return either a function pointer or a SIG_ERR value, which happens to be -1.

The man page for the "signal" system call provides the following information...

>  #include <signal.h>
>  typedef void (*sighandler_t)(int);
>  sighandler_t signal(int signum, sighandler_t handler);
...
>RETURN VALUE
>The signal() function returns the previous value of the signal handler,
>or SIG_ERR on error.

The following is my attempt at a solution which works fine if I don't use the enum type SIG_ERR to check for a return error condition from signal(...)

typedef void function(int) sighandler_t;
enum : sighandler_t
{
  SIG_ERR = (sighandler_t)-1, /* Error return.   */
  SIG_DFL = (sighandler_t)0,  /* Default action. */
  SIG_IGN = (sighandler_t)1   /* Ignore signal.  */
}
extern (C)
{
 void function(int) signal(int signum, void function(int) sighandler_t);
}

With the above declarations the following code fragment seems to work as expected.
signal(SIGINT, exit_program);

where the function exit_program(int) is declared as...
extern (C)
{
   void exit_program(int signum)
   {
      // some code
   }
}

but the next code fragment generates a compiler error...

sighandler_t rval;
rval = signal(SIGINT, exit_program);

main.d(50): cannot implicitly convert void(C *)(int) to sighandler_t

but I thought the typedef gave me a type sighandler_t of void(C *)(int) or have I totally missed something?

Any suggestions 'cause I'm really not sure what I'm doing here!

Simon J Mackenzie

Need to put the typedef for sighandler_t inside an extern (C).

"Simon J Mackenzie" <project.d@smackoz.fastmail.fm> wrote in message news:bfbt85$3094$1@digitaldaemon.com...
> I need help trying to sort out a declaration for a system call to Linux but I'm not sure how to handle the situation where the function can return either a function pointer or a SIG_ERR value, which happens to
be -1.
>
> The man page for the "signal" system call provides the following information...
>
>  >  #include <signal.h>
>  >  typedef void (*sighandler_t)(int);
>  >  sighandler_t signal(int signum, sighandler_t handler);
> ...
>  >RETURN VALUE
>  >The signal() function returns the previous value of the signal handler,
>  >or SIG_ERR on error.
>
> The following is my attempt at a solution which works fine if I don't use the enum type SIG_ERR to check for a return error condition from signal(...)
>
> typedef void function(int) sighandler_t;
> enum : sighandler_t
> {
>    SIG_ERR = (sighandler_t)-1, /* Error return.   */
>    SIG_DFL = (sighandler_t)0,  /* Default action. */
>    SIG_IGN = (sighandler_t)1   /* Ignore signal.  */
> }
> extern (C)
> {
>   void function(int) signal(int signum, void function(int) sighandler_t);
> }
>
> With the above declarations the following code fragment seems to work as
> expected.
> signal(SIGINT, exit_program);
>
> where the function exit_program(int) is declared as...
> extern (C)
> {
>     void exit_program(int signum)
>     {
>        // some code
>     }
> }
>
> but the next code fragment generates a compiler error...
>
> sighandler_t rval;
> rval = signal(SIGINT, exit_program);
>
> main.d(50): cannot implicitly convert void(C *)(int) to sighandler_t
>
> but I thought the typedef gave me a type sighandler_t of void(C *)(int)
> or have I totally missed something?
>
> Any suggestions 'cause I'm really not sure what I'm doing here!
>
> Simon J Mackenzie
>