Question

我在处理“CTRL-C”信号时遇到了一些问题，我需要的是handle_SIGINT只输出一次，然后让它返回到setup函数中的读取，但我不知道如何要解决这个问题。有人告诉我在length = read call周围添加一个循环，因为read是一个阻塞调用。我只是对如何处理这些信号感到困惑。无论如何，我目前的输出是：

COMMAND->test
COMMAND->test2
COMMAND->test3
COMMAND->test4
COMMAND->^CFound your CTRL-C
Found your CTRL-C
COMMAND->Found your CTRL-C
COMMAND->Found your CTRL-C
COMMAND->error reading the command: Interrupted system call
^Z
Suspended


#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>

#define MAX_LINE 80 /* 80 chars per line, per command, should be enough. */

void handle_SIGINT()
{
  printf("Found your CTRL-C\n");
}

void setup(char inputBuffer[], char *args[],int *background)
{
    int length, /* # of characters in the command line */
         i,      /* loop index for accessing inputBuffer array */
         start,  /* index where beginning of next command parameter is */
        ct;     /* index of where to place the next parameter into args[] */

     ct = 0;

     /* read what the user enters on the command line */
     length = read(STDIN_FILENO, inputBuffer, MAX_LINE);  

     start = -1;
     if (length == 0)
        exit(0);            /* ^d was entered, end of user command stream */
     if (length < 0){
        perror("error reading the command");
    exit(-1);           /* terminate with error code of -1 */
    }

     /* examine every character in the inputBuffer */
     for (i = 0; i < length; i++) { 
        switch (inputBuffer[i]){
        case ' ':
        case '\t' :               /* argument separators */
            if(start != -1){
                args[ct] = &inputBuffer[start];    /* set up pointer */
                ct++;
            }
            inputBuffer[i] = '\0'; /* add a null char; make a C string */
            start = -1;
            break;

        case '\n':                 /* should be the final char examined */
            if (start != -1){
                args[ct] = &inputBuffer[start];     
                ct++;
            }
            inputBuffer[i] = '\0';
            args[ct] = NULL; /* no more arguments to this command */
            break;

        case '&':
            *background = 1;
            inputBuffer[i] = '\0';
            break;

        default :             /* some other character */
            if (start == -1)
                start = i;
    } 
    }    
    args[ct] = NULL; /* just in case the input line was > 80 */
} 

int main(void)
{
    char inputBuffer[MAX_LINE]; /* buffer to hold the command entered */
    int background;             /* equals 1 if a command is followed by '&' */
    char *args[MAX_LINE/2+1];/* command line (of 80) has max of 40 arguments */

    struct sigaction handler;
    handler.sa_handler = handle_SIGINT;
    sigaction(SIGINT, &handler, NULL);

    while (1){            /* Program terminates normally inside setup */
        background = 0;
    printf("COMMAND->");
        fflush(0);
        setup(inputBuffer, args, &background);       /* get next command */

        int pid;

    pid = fork(); /* for a child process */

    if (pid < 0) { /* check if error occurred with child process */
      fprintf(stderr, "Fork Failed");
      return 1;
    } else if (pid == 0) { /* child process */
      execvp(args[0], args);
    } else {
      if (background == 0){ /* check if the parent should wait */
        //wait(args);
        waitpid(pid, NULL, 0);
      }
    }

    /* the steps are:
      (1) fork a child process using fork()
      (2) the child process will invoke execvp()
      (3) if background == 0, the parent will wait, 
        otherwise returns to the setup() function. */
    }
}

Answer 1

当read（）返回-1时，检查errno - 如果是EINTR，则返回执行再次读取。 EINTR表示阻塞系统调用（在我们的例子中是read（））被信号中断，因此您可以安全地返回执行一次读取

   EINTR  The call was interrupted by a signal before any data was read; see signal(7).

从另一方面来看，在很多情况下按CTRL + C表示用户想要终止程序，因此退出该程序是预期的行为。

Answer 2

告诉程序在打印消息后忽略handle_SIGINT中的SIGINT信号。

void handle_SIGINT()
{
  printf("Found your CTRL-C\n");
  signal(SIGINT, SIG_IGN);
}

Answer 3

这是您应该使用sigaction()编写的：

struct sigaction new_handler,old_handler;

new_handler.sa_handler=handle_SIGINT;
sigemptyset(&new_handler.sa_mask);
new_handler.sa_flags=0;

sigaction(SIGINT,NULL, &old_handler);
if(old_handler.sa_handler != SIG_IGN)
   sigaction(SIGINT, &new_handler,NULL);

Answer 4

作为建议，尽量让你的程序尽可能便携，我的意思是，在我看来，你可以用ANSI C编写大量的程序。

考虑使用fgets（）而不是read（），并且不要依赖行为，即使这种行为已被充分记录为bimda指出它。

void setup(char inputBuffer[], char *args[],int *background)
{
    char *ret; 
    int length; /* # of characters in the command line */
    int i;      /* loop index for accessing inputBuffer array */
    int start=-1;  /* index where beginning of next command parameter is */
    int ct=0;     /* index of where to place the next parameter into args[] */


     /* read what the user enters on the command line */
     ret = fgets(inputBuffer, MAX_LINE, stdin);  

     if(!ret)
        exit(0);            /* ^d was entered, end of user command stream */

    /* examine every character in the inputBuffer */
    for (i = 0; inputBuffer[i]; i++) {
            ...
    }
    ...
}

和作为patater的C-c部分说：

void handle_SIGINT()
{
    printf("Found your CTRL-C\n");
    signal(SIGINT, SIG_IGN);
}

〜$ man signal

也许这不是你需要的，但这只是我的拙见。

Answer 5

正如其他人所说，我只是添加一个while循环：

while((length = read(STDIN_FILENO, inputBuffer, MAX_LINE) == -1);

在我的简单shell程序中需要帮助处理“CTRL-C”信号

5 个答案: