写入管道总是失败

Question

I am trying to communicate between 2 processes by trying to read data from text file into first pipe and read it on the other one but the write function always fails:

Main:

int main(int argc, char* argv[])
{
    int readerPip[2], writerPip[2], reader, writer;

    if (pipe(readerPip))
    {
      fprintf (stderr, "Pipe failed.\n");
      return EXIT_FAILURE;
    }

    if(pipe(writerPip))
    {
      fprintf (stderr, "Pipe failed.\n");
      return EXIT_FAILURE;
    }

    close(readerPip[1]); // closing reader writing side pipe for main thread
    reader = fork();
    if (reader < 0)
    {
        perror("Cannot fork()");
        exit(EXIT_FAILURE);
    }
    else if (reader == 0)
    {
        do_reader(readerPip);
    }

    wait(NULL);
    close(writerPip[0]); // closing writer reader side pipe for main thread
    do_father(readerPip, writerPip);
    close(readerPip[0]); // closing reader reader side pipe for main thread
    close(writerPip[1]); // closing writer writing side pipe for main thread
    writer = fork();

    if (writer < 0)
    {
        perror("Cannot fork()");
        exit(EXIT_FAILURE);
    }
    else if (writer == 0)
    {
        do_writer(writerPip);
    }

    return 1;
}// main

do_Reader:

void do_reader(int readerPipe[])
{
    char stringCommand[17];
    long long unsigned command;

    close(readerPipe[0]);
    while (1)
    {
        scanf("%s", stringCommand);
        command = convertStringToPolygon(stringCommand);

        if ((command & 0xFFFFFFFF) == 0xFFFFFFFF)
        {
            break;
        }

        if (write(readerPipe[1], stringCommand, strlen(stringCommand) ) == -1)
        {
            printf("writing falied");
        }
        else
        {
            printf("success");
        }

        printf("\n");
    }

    close(readerPipe[1]);
    exit(0);
}

do_father

void do_father(int readerPipe[], int writerPipe[])
{
    long long unsigned nbytes;
    char currentPolygon[17];
    currentPolygon[16] = '\0';
    while (1)
    {
        nbytes = read(readerPipe[0], currentPolygon, sizeof(currentPolygon));
        if (nbytes == 0)
        {
            printf("done");
            break;
        }

        manageProgram(readerPipe, writerPipe,        convertStringToCommand(currentPolygon));
    }
}

do_writer

void do_writer(int pip[])
{
    close(pip[1]);
    long long unsigned command, nbytes;

    while (1)
    {
    nbytes = read(pip[0], &command, sizeof(command));
        if (nbytes == 0)
        {
            break;
        }
        if ((((command & THIRD_BIT_MASK) != FALSE) || ((command & FORTH_BIT_MASK) 
!= FALSE) ||
            ((command & FIFTH_BIT_MASK) != FALSE)) != FALSE)
            generateOutputDependsOnBits(command);
    }

    close(pip[0]);
    exit(0);
}

the rest of the code does not matter since writing for the reader pipe does not working. the text file looks like this:

3a 0000050000050505 3e 003cc40000c43c3c ba 000088ec9c32ce32 f8 cc 3a 000085ec9a32cd32 4c 8c 5c ac fd FFFFFFFFFFFFFFFF

Answer 1

You close readpipe[1] in main ( before the fork ) and close readpipe[0] in do_reader , so both sides of the pipe are closed in the child.

Move the close(readpipe[1]) in main farther down (eg before the wait ).

But, you may not want to wait there. You may want to do it after do_father as this would rely upon the kernel pipe buffers being large enough to hold all the data the child sends to the parent before the parent even tries to get the first byte.