Question

我编写了一个程序（包含来自SO的代码）printenv | sort | less，现在我应该实现错误处理。怎么办？程序应该优雅地失败，例如在传递错误的参数时。

#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
struct command
{
    const char **argv;
};
/* Helper function that spawns processes */
int spawn_proc (int in, int out, struct command *cmd) {
    pid_t pid;
    if ((pid = fork ()) == 0) {
        if (in != 0) {
            dup2 (in, 0);
            close (in);
        }
        if (out != 1) {
            dup2 (out, 1);
            close (out);
        }
        return execvp (cmd->argv [0], (char * const *)cmd->argv);
    }
    return pid;
}
/* Helper function that forks pipes */
int fork_pipes (int n, struct command *cmd) {
    int i;
    int in, fd [2];
    for (i = 0; i < n - 1; ++i) {
        pipe (fd);
        spawn_proc (in, fd [1], cmd + i);
        close (fd [1]);
        in = fd [0];
    }
    dup2 (in, 0);
    return execvp (cmd [i].argv [0], (char * const *)cmd [i].argv);
}

int main (int argc, char ** argv) {
    int i;
    if (argc == 1) { /* There were no arguments */
        const char *printenv[] = { "printenv", 0};
        const char *sort[] = { "sort", 0 };
        const char *less[] = { "less", 0 };
        struct command cmd [] = { {printenv}, {sort}, {less} };
        return fork_pipes (3, cmd);
    }
    if (argc > 1) { /* I'd like an argument */

        if (strncmp(argv[1], "cd", 2) && strncmp(argv[1], "exit", 2)) {
            char *tmp;
            int len = 1;
            for( i=1; i<argc; i++)
            {
                len += strlen(argv[i]) + 2;
            }
            tmp = (char*) malloc(len);
            tmp[0] = '\0';
            int pos = 0;
            for( i=1; i<argc; i++)
            {
                pos += sprintf(tmp+pos, "%s%s", (i==1?"":"|"), argv[i]);
            }
            const char *printenv[] = { "printenv", 0};
            const char *grep[] = { "grep", "-E", tmp, NULL};
            const char *sort[] = { "sort", 0 };
            const char *less[] = { "less", 0 };
            struct command cmd [] = { {printenv}, {grep}, {sort}, {less} };
            return fork_pipes (4, cmd);
            free(tmp);
        } else if (! strncmp(argv[1], "cd", 2)) { /* change directory */
            printf("change directory to %s\n" , argv[2]);
            chdir(argv[2]);
        } else if (! strncmp(argv[1], "exit", 2)) { /* change directory */
            printf("exit\n");
            exit(0);
        }
    }
    exit(0);
}

Answer 1

坦白地说，通过你的程序并在事后修复所有那些丢失错误处理的错误会有点痛苦。从一开始就编写正确的代码会好得多！此外，你有更多的错误，而不仅仅是错过错误处理。我没有扫描你的所有代码，但乍一看我已经看到一个未初始化的局部变量的使用（in中的fork_pipes在设置之前使用）。任何启用了警告的合适编译器都会抓住它。

作为对您的问题的直接回答，您只需要查看能够返回错误的每个系统调用或库函数调用，看看您是否正在检查它们，并添加检查还没有。 fork，malloc，dup2 - 一切。

我的程序应如何处理错误？

1 个答案: