由于指针 (C)，流水线理念不起作用

Question

前段时间我在做一个小程序，我想把它缩短。

这个小程序是关于一个线程创建多个 child 的线程，这些 child 将使用管道按顺序将其标准 output/input 重定向到另一个，除了最后一个 child，谁不会' t 重定向它的标准输出，像这样。

Parent pipe  child1   pipe   child2  pipe   last child
       __             __             __
O-----|__|-----O-----|__|-----O-----|__|-----O -> Stdout

我第一次面对这段代码，我做了一个维度为[n_child][2]的矩阵，并从那个矩阵的每个位置做了一个管道，所以很容易连接每个需要时通过管道传输到每个 child。但现在我只想用 2 个管道尝试它，"playing" 继承。

也许我没有很好地解释自己，所以我认为用我的代码可以更好地理解所有内容，所以我们开始吧。

piping_function(int number_of_child){

    int i;
    int olddesc[2];
    int newdesc[2]; //Here I create the descriptors of the pipes I'll use
    int *olddir;
    int *newdir;
    if(pipe(olddesc)<0 || pipe(newdesc) < 0){  //I create the pipes
        //Error 
    }
    olddir = olddesc;
    newdir = newdesc; //And attach the directions to the array's direction (we will see later why)
    for(i = 0; i < number_of_child; i++){
        chaddr[i] = fork();
        switch(chaddr[i]){
            case -1:
                //Error trace
            case 0:
                dup2(olddesc[0],0); //Here I redirect the pipe who connect the previous child's pipe to the standard input
                if(i != number_of_child - 1)
                    dup2(newdesc[1],1); //And here, except from the last child, I redirect the standard output to the pipe who will connect to the standard input of the next child
                close(olddesc[0]);
                close(newdesc[1]); //I close the descriptors I don't need
                //Several child operations with standard input-output (end up returning 0/1 after the pipeline is connected, so no child will create any child)
            default:
                if(i == 0)
                    dup2(olddesc[1], 1); //I want the standard output of the principal proccess only on the first pipe
                olddir = newdir; //Here I would want the direction of the "old" pipe to be the direction of the "new" pipe, in order to achieve the pipeline
                if(pipe(newdesc)<0)
                    //Error
                break;
        }//End of switch
    }//End of for
    close(olddesc[0]);close(olddesc[1]);close(newdesc[0]);close(newdesc[1]); //I don't need these descriptors anymore, as they must be redirected to the standard's input/output of the process they need.
}//End of function

嗯，这是我的代码。我想我可以看到我正在做的错误，当我让 olddir 成为 newdir 并创建管道时，我正在做 olddir 也是那个新管道，对吗？那么我的问题来了：

有什么方法可以实现这种改变吗？我的意思是，我想要的是将 olddir（谁是 olddesc 的地址，对吗？所以如果我更改该地址，olddesc 的地址也会更改，对吗？）等于 newdir，以便继续我之前创建的管道重定向 "next" child 的标准输出，但我也希望 newdir 成为一个新管道。

我真的不知道我的解释是否正确，我不是母语人士，用其他语言解释这些想法有点困难。随时纠正任何语法错误，我将不胜感激，并提出有关代码的任何问题，因为我可能没有给出我想要的观点。

谢谢。

Answer 1

好吧，我终于做到了，但是改变了观点，不使用任何地址覆盖，只玩迭代，以便始终保持两个管道之一的记录。我并没有真正解决地址问题，但它确实有效，我很满意。

piping_function(int number_of_child){

    int i;
    int olddesc[2];
    int newdesc[2]; //Here I create the descriptors of the pipes I'll use

    //Now we'll start from the last pipe, so we can connect the parent to the first one and not connect the last child's output.
    for(i = number_of_child - 1; i >= 0; i--){
        //Instead of changing addresses, I'll play with the "i"
        if(i%2==0){
            close(newdesc[0]); //We close the last descriptors 
            close(newdesc[1]);
            pipe(newdesc); //And create a new pipe!
        }
        else{
            close(olddesc[0]);
            close(olddesc[1]);
            pipe(oldesc);
        }
        chaddr[i] = fork();
        switch(chaddr[i]){
            case -1:
                //Error trace
            case 0:
                if(i%2==0){
                    dup2(newdesc[0],0); //Here I redirect the pipe who connect the previous child's pipe to the standard input
                    if(i != number_of_child - 1)
                        dup2(olddesc[1],1); //And here, except from the last child, I redirect the standard output to the pipe who will connect to the standard input of the next child
                    close(newdesc[1]);
                    close(olddesc[0]); //I close the descriptors I don't need    
                }
                else{
                    dup2(olddesc[0],0); //Here I redirect the pipe who connect the previous child's pipe to the standard input
                    if(i != number_of_child - 1)
                        dup2(newdesc[1],1); //And here, except from the last child, I redirect the standard output to the pipe who will connect to the standard input of the next child
                    close(olddesc[1]);
                    close(newdesc[0]); //I close the descriptors I don't need
                }
                //Several child operations with standard input-output (end up exiting 0/1 after the pipeline is connected, so no child will create any child)
            default:
                if(i == 0)
                    dup2(newdesc[1], 1); //I want the standard output of the principal proccess only on the first pipe
                break;
        }//End of switch
    }//End of for
    close(olddesc[0]);close(olddesc[1]);close(newdesc[0]);close(newdesc[1]); //I don't need these descriptors anymore, as they must be redirected to the standard's input/output of the process they need.
}//End of function

*编辑：

我认为总是关闭描述符是不好的，即使没有创建任何东西，我看到我在这段代码中以这种方式保留了它们，但为了使其正常工作，我们应该只关闭描述符创建时，每次关闭时都需要一个 if。

由于指针 (C)，流水线理念不起作用

Pipeline idea not working due to pointers (C)

c

redirect

pointers

pipeline

parent-child