Question

我试图使用fork，pipe，dup2和execvp编写无名管道程序。程序应该从命令行获取第一个命令，并分叉子进程。父进程应执行命令并将输出传递给子进程。孩子应该继续下一个命令（令牌是＆＃39; - ＆＃39;而不是常规的管道标志＆＃39; |＆＃39;）并在父母的输入上进行，依此类推，所以每个父节点的输出传递给子节点，直到最后一个应该在主节点和节点上执行的命令。出于某种原因，该程序似乎在打印之前停止在dup2＆＃34; parent2！＆＃34;。提前感谢所有的帮助：）

#include <stdio.h>
#include <dirent.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h> // for open flags
#include <time.h> // for time measurement
#include <assert.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>

#define LINE_MAX 1024

char* buffer[LINE_MAX];


void np_exec(char* cmd, char** argv)
{
int i,len=0,ret_p,ret_c;
int mypipefd[2];

/* count how many args till NULL to know how much space to allocate */
for(i=0;argv[i]!=NULL;i++)
    len++;
if (len == 0)
{
    printf("ERROR_CMD\n");
    exit(EXIT_FAILURE);
}
char* par[len+1];
par[len] = NULL;

/* creat parameters array */
for(i=0;argv[i]!=NULL;i++)
    par[i] = argv[i];

/* creat pipe */
if (pipe(mypipefd)==-1)
{
    printf("ERROR_PIPE: %s\n", strerror(errno));
    exit(EXIT_FAILURE);
}
pid_t cpid;
cpid = fork();
if (cpid == -1)
{
    printf("FORK_ERROR: %s\n", strerror(errno));
    exit(EXIT_FAILURE);
}
/* child process */
else if (cpid==0)
{
    printf("child!\n");//TODO delete
    dup2(mypipefd[0], STDIN_FILENO);
    close(mypipefd[1]);
    if(read(STDIN_FILENO,buffer,LINE_MAX)<0) //read output from pipe.
    {
        printf("READ_ERROR: %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
    printf("child2!\n");//TODO delete
}
/* parent process */
else
{
    printf("parent!\n");//TODO delete
    dup2(mypipefd[1], STDOUT_FILENO);
    printf("parent2!\n");//TODO delete
    close(mypipefd[0]); //Closes read side of pipe
    if (execvp(cmd,par) == -1)
    {
        printf("EXECVP_ERROR: %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
}
}

int main(int argc, char** argv)
{
/* last char is not '-' */
assert(strcmp(argv[argc-1], "-"));

/*The program then parses the arguments,
 * calling the function np_exec for each separate set of arguments except the last,
 *  i.e., list of arguments that end with a minus character.*/
int i;
for (i = 1; i < argc; ++i) {
    if (!strcmp(argv[i], "-")) {
        argv[i] = NULL;
        np_exec(argv[1], &argv[1]);
        /* support milti pipes */
        argv = &argv[i];
        argc -= i;
        i = 0;
    }
}

/* array for the final program in the arguments */
char* args[argc];
args[argc-1] = NULL;

/* let it start from index 0 */
for (i = 1; i < argc; ++i) {
    args[i-1] = argv[i];
}
printf("finish!!!\n");//TODO delete
/* execute the final program in the arguments using execvp */
if (execvp(args[0], args) == -1)
    perror("execvp failed");
return;

}

dup2函数不返回任何值

0 个答案: