C99: qual è il modo consigliato a gestire le eccezioni sollevate da `pow()` (overflow o numero complesso)

Question

esecuzione

double result = pow(base, exponent); 

con arbitraria base e exponent

può comportare un tentativo di calcolare un valore troppo grande o complesso.

Ad esempio con base=-2, exponent=.5 (radice quadrata di -2)

devo solo controllare se result==NAN o result==HUGE_VAL?

Tale codice deve essere conforme a C99 e multipiattaforma?

Answer 1

Cattura SIGFPE e muore rumorosamente. C'è qualcosa di peggio di un programma in crash: uno che dà tranquillamente risposte sbagliate.

codice di esempio riportato di seguito è tratto from a random site about SIGFPE

/* demo_SIGFPE.c 

    Demonstrate the generation of the SIGFPE signal. 

    Usage: demo_SIGFPE [optstr] 

    The main program executes code the generates a SIGFPE signal. Before doing 
    so, the program optionally ignores and/or blocks SIGFPE. If 'optstr' 
    contains 'i', then SIGFPE is ignored, otherwise it is caught by a handler. 
    If 'optstr' contains 'b', then SIGFPE is blocked before it is delivered. 
    The behavior that occurs when SIGFPE is generated depends on the kernel 
    version (Linux 2.6 is different from Linux 2.4 and earlier). 

    NOTE: Don't compile this program with optimization, as the arithmetic 
    below is likely to be optimized away completely, with the result that 
    we don't get SIGFPE at all. 
*/ 
#define _GNU_SOURCE  /* Get strsignal() declaration from <string.h> */ 
#include <string.h> 
#include <signal.h> 

static void 
sigfpeCatcher(int sig) 
{ 
    printf("Caught signal %d (%s)\n", sig, strsignal(sig)); 
           /* UNSAFE (see Section 21.1.2) */ 
    sleep(1);     /* Slow down execution of handler */ 
} 

int 
main(int argc, char *argv[]) 
{ 
    int x, y; 
    sigset_t blockSet, prevMask; 
    Boolean blocking; 
    struct sigaction sa; 

    /* If no command-line arguments specified, catch SIGFPE, else ignore it */ 

    if (argc > 1 && strchr(argv[1], 'i') != NULL) { 
     printf("Ignoring SIGFPE\n"); 
     if (signal(SIGFPE, SIG_IGN) == SIG_ERR) 
      errExit("signal"); 
    } else { 
     printf("Catching SIGFPE\n"); 
     sigemptyset(&sa.sa_mask); 
     sa.sa_flags = SA_RESTART; 
     sa.sa_handler = sigfpeCatcher; 
     if (sigaction(SIGFPE, &sa, NULL) == -1) 
      errExit("sigaction"); 
    } 

    blocking = argc > 1 && strchr(argv[1], 'b') != NULL; 
    if (blocking) { 
     printf("Blocking SIGFPE\n"); 
     sigemptyset(&blockSet); 
     sigaddset(&blockSet, SIGFPE); 
     if (sigprocmask(SIG_BLOCK, &blockSet, &prevMask) == -1) 
      errExit("sigprocmask"); 
    } 

    printf("About to generate SIGFPE\n"); 
    y = 0; 
    x = 1/y; 
    y = x;  /* Avoid complaints from "gcc -Wunused-but-set-variable" */ 


    if (blocking) { 
     printf("Sleeping before unblocking\n"); 
     sleep(2); 
     printf("Unblocking SIGFPE\n"); 
     if (sigprocmask(SIG_SETMASK, &prevMask, NULL) == -1) 
      errExit("sigprocmask"); 
    } 

    printf("Shouldn't get here!\n"); 
    exit(EXIT_FAILURE); 
}