C99:处理由`pow()`(溢出或复数)引发的异常的推荐方法是什么？

Question

执行

double result = pow(base, exponent);

任意base和exponent

可能导致尝试计算太大或太复杂的值.

例如base=-2,exponent=.5(-2的平方根)

如果我只是检查,如果result==NAN还是result==HUGE_VAL？

该代码是否符合C99和跨平台？

Answer 1

捕获 SIGFPE 并大声死亡。有比崩溃的程序更糟糕的事情：悄悄地给出错误的答案。

下面的示例代码取自有关 SIGFPE 的随机站点

/* 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);
}