Numeriske fejl

madsen666>>

Som du selv er inde på så skal du bruge exceptions til dit for mår altså :


var
  d,e : Double;
begin
  d := 7;
  try
    e:= d/0
  execpt
    ShowMessage(\'NAR !! Det kan man da ikke\');
  end;
end;

Jens B

Hov borrisholt,
det var da vist ikke C++, hva.... :-)

så prøver vi da abre i C++ i stedet ...

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  double d,e;
  d = 7;
  try
  {
  e = d/0;
  }
  catch(...)
  {
    ShowMessage(\"Nar !! Det kan man da ikke\");
  }
}


Jens B

Tak! Det var lige hvad der skulle til :)

Så ved du også hvordan man gøre i Delphi :-)

Jens B

Syntes nok det mindede mig om pascal.... =8-)

Troede lige, at det virkede, men det gør det ikke. Prøv følgende program:

#include <iostream>

void main(){
  double a=1.2;
  double b=0;
  double c;
  try{
    c=a/b;
  }catch(...){
    cout << \"Caught you!!!\\n\";
  }
  cout << c << \"\\n\";
}

Jeg får som output:

[madsen@batman Dilaton]$ g++ tst.cpp
[madsen@batman Dilaton]$ ./a.out
inf

Altså ingen exception :( Hvorfor det? Og hvordan laver man egnetligt noget der svarer til:

if (a==inf || a==nan){
  cout << \"No way\\n\";
}

Ovenstående virker dog fint hvis jeg selv smider en exception med \"throw\"....

Her et lille C - eksempel der håndter fejl vha. setjmp og longjmp.

#include <stdio.h>
#include <signal.h>
#include <setjmp.h>
#include <stdlib.h>
#include <float.h>
#include <math.h>
#include <string.h>

jmp_buf mark;              /* Address for long jump to jump to */
int    fperr;            /* Global error number */

void __cdecl fphandler( int sig, int num );  /* Prototypes */
void fpcheck( void );

void main( void )
{
  double n1, n2, r;
  int jmpret;
  /* Unmask all floating-point exceptions. */
    _control87( 0, _MCW_EM );
  /* Set up floating-point error handler. The compiler
    * will generate a warning because it expects
    * signal-handling functions to take only one argument.
    */
    if( signal( SIGFPE, fphandler ) == SIG_ERR )

  {
      fprintf( stderr, \"Couldn\'t set SIGFPE\\n\" );
      abort();  }

  /* Save stack environment for return in case of error. First
    * time through, jmpret is 0, so true conditional is executed.
    * If an error occurs, jmpret will be set to -1 and false
    * conditional will be executed.
    */
  jmpret = setjmp( mark );
  if( jmpret == 0 )
  {
      printf( \"Test for invalid operation - \" );
      printf( \"enter two numbers: \" );
      scanf( \"%lf %lf\", &n1, &n2 );
      r = n1 / n2;
      /* This won\'t be reached if error occurs. */
      printf( \"\\n\\n%4.3g / %4.3g = %4.3g\\n\", n1, n2, r );

      r = n1 * n2;
      /* This won\'t be reached if error occurs. */
      printf( \"\\n\\n%4.3g * %4.3g = %4.3g\\n\", n1, n2, r );
  }
  else
      fpcheck();
}
/* fphandler handles SIGFPE (floating-point error) interrupt. Note
* that this prototype accepts two arguments and that the
* prototype for signal in the run-time library expects a signal
* handler to have only one argument.
*
* The second argument in this signal handler allows processing of
* _FPE_INVALID, _FPE_OVERFLOW, _FPE_UNDERFLOW, and
* _FPE_ZERODIVIDE, all of which are Microsoft-specific symbols
* that augment the information provided by SIGFPE. The compiler
* will generate a warning, which is harmless and expected.

*/
void fphandler( int sig, int num )
{
  /* Set global for outside check since we don\'t want
    * to do I/O in the handler.
    */
  fperr = num;
  /* Initialize floating-point package. */
  _fpreset();
  /* Restore calling environment and jump back to setjmp. Return
    * -1 so that setjmp will return false for conditional test.
    */
  longjmp( mark, -1 );
}
void fpcheck( void )
{
  char fpstr[30];
  switch( fperr )
  {
  case _FPE_INVALID:
      strcpy( fpstr, \"Invalid number\" );
      break;
  case _FPE_OVERFLOW:
      strcpy( fpstr, \"Overflow\" );

      break;
  case _FPE_UNDERFLOW:
      strcpy( fpstr, \"Underflow\" );
      break;
  case _FPE_ZERODIVIDE:
      strcpy( fpstr, \"Divide by zero\" );
      break;
  default:
      strcpy( fpstr, \"Other floating point error\" );
      break;
  }
  printf( \"Error %d: %s\\n\", fperr, fpstr );
}