c - 在 C 中处理 SIGINT

Question

我正在尝试在 C 代码中处理 SIGINT，但得到以下输出，但我不确定原因

COMMAND->hello
COMMAND->world
COMMAND->test
COMMAND->^CI don't know! 
error reading the command: Interrupted system call

这是我的代码:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <signal.h>
#include <string.h>

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


//The function used to handle the signal:
void handle_SIGINT(){
    printf("I don't know! \n");
    fflush(stdout);
}

/**
 * setup() reads in the next command line, separating it into distinct tokens
 * using whitespace as delimiters. setup() sets the args parameter as a 
 * null-terminated string.
 */

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 */

    //Setup the signal handler
    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 */

    /* 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. */

     //The fork
     pid_t pid = fork();

     //If it is the child, execute the code
     if(pid == 0){
            execvp(inputBuffer, args);
            exit(0);
        }
    if(background == 0){
        wait(NULL);
    }

    }
}

我希望能够返回“命令行”并继续检查输入。

Answer 1

您的程序正在执行您告诉它的操作，即，当读取返回任何类型的错误时退出:

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

start = -1;
if (length == 0)
    exit(0);
if (length < 0){
    perror("error reading the command");
    exit(-1);   // <----- Exit at any kind of error
}

来自read(2)手册页:

On error, -1 is returned, and errno is set appropriately. In this case, it is left unspecified whether the file position (if any) changes.

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

读取后检查错误是否为信号中断(包括errno.h):

length = 0;
while (length <= 0) {
    printf("COMMAND->");
    fflush(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 && errno != EINTR) {
        perror("error reading the command");
        exit(-1);           /* terminate with error code of -1 */
    }
}