C99：什麼是處理通過`POW引發的異常（）`

Question

執行

double result = pow(base, exponent); 

任意base和exponent

可能會導致在試圖計算（溢出或複數）的recomended方式價值太大或太複雜。

例如與base=-2，exponent=.5（-2的平方根）

我應該檢查是否result==NAN或result==HUGE_VAL？

該代碼是否符合C99和跨平臺？

Answer 1

抓住SIGFPE並嘶嘶作響。有一些比墜毀的程序更糟糕：一個悄悄地給出不正確的答案。下面

示例代碼採取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); 
}