如何為另一個程序運行命令usig sys調用“ execvp”

Question

我寫了一個comp.out，它接受2個主argv參數並在文件之間進行比較。 主機必須返回值1,2,3，其中3表示相同，2表示幾乎相同，1表示不相同。 exmp：在另一個程序中，我試圖應用我編寫的“ comp.out”。./comp.out /home/demo/code/1.txt /home/demo/code/2.txt 問題是我需要知道它的返回狀態並使其工作。 我注意到我在execvp命令中收到了“ -1”。 這是我到目前為止編寫的代碼。

那么如何執行“ comp.out”命令？

感謝您的幫手！

void compareOutputFiles(char *path, char *arg2) {
    pid_t   runner;
    char *cmd [] = {"./comp.out",path, arg2, NULL};
    int status;
    int savedFD     = dup(0);
    int dirchange   = chdir(path);
    int fdin, fdout;

    strcat(path, "/output.txt");
    cmd[1] = path;
    fdin    = open(path,O_RDONLY);


    dup2(fdin,  0);


    if ((runner = fork()) < 0) {perror("could not make fork");}
    else if (runner == 0) {
                execvp(cmd[0],cmd); ->>>>>>>>>>>>returns -1
                exit(0);
    } else if (runner != 0) {
        waitpid(runner,&status,0);
        printf("return val :%d\n", (status));

    }
    dup2(savedFD, 0);
    close(fdin);
} 

Answer 1

根據man waitpid說法，您傳遞給status的參數未完全設置為子進程的返回碼，而是可以由各種宏檢查的值，包括

   WIFEXITED(status)
          returns true if the child terminated normally, that is, by calling exit(3) or _exit(2), or by returning from main().

   WEXITSTATUS(status)
          returns  the  exit status of the child.  This consists of the least significant 8 bits of the status argument that the child specified in a call to exit(3) or _exit(2) or as
          the argument for a return statement in main().  This macro should be employed only if WIFEXITED returned true.

因此您的代碼應該看起來像這樣：

waitpid(runner,&status,0);
printf("status: %d\n", (status));
//probably exit here or return error if child died
printf("finished normally: %d\n", WIFEXITED(status));
printf("return code: %d\n", WEXITSTATUS(status));