Question

长期以来,我一直在寻求解决我的问题,因为这样,我为什么要向你们说:

Consider this piece of code:

static char done = 0;
static void sigHandler(void)
{
    done = 1;
}

int user_input()
{
    return (getchar() ==  q ) ? 0 : 1;
}

int main(void)
{
    signal(SIGTERM, sigHandler);
    signal(SIGINT, sigHandler);
    while (user_input() != 0 && !done)
        usleep(1000);
    printf("exiting
");
    return 0;
}

Expected behavior: The program exits when user inputs q then enter. If CTRL+C is pressed, it is caught by the sigHandler function which sets the flag done to 1 and exits the program.

Observed behavior: The CTRL+C character is eaten by the getchar() call, and the sigHandler function is never executed. When CTRL+C and then enter is pressed, the sigHandler function is called and the program exits.

具有更多经验和知识的人能否帮助我了解这一点?

感谢您的投入:

Answer 1

在那里,可以绕过呼吁而不诉诸于ug(当然还有保罗·R所说的话)。请使用<代码>sigaction() with sa_flags set to 0 undsignal(。

此外,信号(2)手册指出:

Avoid its use: use sigaction(2) instead.

#include <stdio.h>
#include <signal.h>
#include <string.h>
#include <errno.h>

static char done = 0;
static void sigHandler(int signum)
{
    done = 1;
}

int user_input()
{
    return (getchar() ==  q ) ? 0 : 1;
}

int main(void)
{
    struct sigaction sa;
    memset(&sa, 0, sizeof(struct sigaction));
    sa.sa_handler = sigHandler;
    sa.sa_flags = 0;// not SA_RESTART!;

    sigaction(SIGINT, &sa, NULL);
    sigaction(SIGTERM, &sa, NULL);

    while (user_input() != 0 && !done)
        usleep(1000);
    printf("exiting
");
    return 0;
}

Normally, after catching and handling a signal, most (I m not sure if not all) syscalls will be restarted. This way, after handling the sigint signal, your getchar function will continue as if nothing happened. You can change this behavior by calling sigaction with sa_flags=0.

这样,在处理SIGINT之后,getchar 将返回-1<>>/code>和errno将被定为“Interrupted system calls”(我不记得现在的不变名称)。



You would also have to rewrite your user_input() function to handle the case when returning -1.

Answer 2


该守则实际上按预期运作——在你从<条码>用户_投入(<>>条码/代码>返回后,你没有测试<条码>done的旗帜,这就是为什么在控制C之后你需要进入额外特性的原因。

如果你想要放弃对<代码>getchar/code>的呼吁。当你获得控制时,你可能不得不做一些简单的事,例如,使用<条码>> >pjmp/longjmp。

Answer 3

The Ctrl- C nature is fooden by the getchar(>> calls, and the sigHandler function isaban.

Ctrl-C is not eaten by getchar; it results in a signal being delivered and sigHandler being run. This sets done and returns. Only then is getchar called, which eats the newline and after that, done is checked so the program exits.

Btw. 信号手持int case, not void/code>。

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