管道上的寫入操作始終是失敗的

Question

我對管道和併發性有點新，並且幾個小時一直對此問題感到沮喪。我很難理解爲什麼這個write操作在我的管道上不斷失敗。我試圖讓子進程通過父進程接收的管道寫入數據。我當前的代碼是這樣的：

#include <unistd.h> 
#include <stdio.h> 
#include <stdlib.h> 
#define MAXSIZE 4096 

int main() { 
    pid_t status; 
    int fd[2]; //The array of file descriptors 

    if (pipe(fd) == -1) { 
     printf("Error piping"); 
    } 

    status = fork(); //Begin the fork process 
    switch (status) { 
     case -1: 
      perror("Error forking"); 
      break; 
     case 0: 
      //Child process 
      close(fd[0]); //Only send data 
      char some_string[15] = "hi there"; 
      if (write(fd[1], some_string, MAXSIZE) == -1) { 
       printf("Error writing to the pipe"); 
      } 
      close(fd[1]); //Close write end 
      exit(1); 
     default: 
      close(fd[1]); //Only receive data 
      char readed[500] = ""; 
      while(read(fd[0], readed, MAXSIZE) != 0) { 
       printf("read this %s\n", readed); 
      } 
      printf("Done reading"); 
      close(fd[0]); 
      break; 
    } 
    return 1; 
} 

不過，我不斷收到消息「錯誤寫入管道」，這意味着write操作失敗的子進程。另一個有趣的事情是，如果我將some_string更改爲字符串文字，此代碼可正常工作，但它永遠不會終止，相反，父進程中的read操作將從STDIN讀取！我不明白爲什麼會發生這種情況，當父母執行時，我們是否有殭屍小孩，所以管道「死亡」？或者，也許父進程終止，我們有一個孤兒？我該如何避免這種情況，以及如何解釋字符串文字中的奇怪行爲呢？任何見解？

Answer 1

您告訴write()讀取數組超出範圍的數據，並允許read()將讀取的數據寫入陣列的超出範圍。這非常糟糕。

只寫入有效數據並限制讀取的長度不會導致超出範圍的訪問。

試試這個：

#include <unistd.h> 
#include <sys/types.h> /* add this to use pid_t */ 
#include <sys/wait.h> /* add this to use wait() */ 
#include <stdio.h> 
#include <stdlib.h> 
/* remove unused MAXSIZE */ 

int main() { 
    pid_t status; 
    int fd[2]; //The array of file descriptors 
    int st; /* variable for receiving the status */ 

    if (pipe(fd) == -1) { 
     printf("Error piping"); 
     return 1; /* return 1 when the execution failed */ 
    } 

    status = fork(); //Begin the fork process 
    switch (status) { 
     case -1: 
      perror("Error forking"); 
      return 1; /* return 1 when the execution failed */ 
      break; 
     case 0: 
      //Child process 
      close(fd[0]); //Only send data 
      char some_string[15] = "hi there"; 
      if (write(fd[1], some_string, sizeof(some_string)) == -1) { 
       printf("Error writing to the pipe"); 
      } 
      close(fd[1]); //Close write end 
      exit(0); /* return 0 if the execution finished successfully */ 
     default: 
      close(fd[1]); //Only receive data 
      char readed[500] = ""; 
      while(read(fd[0], readed, sizeof(readed) - 1) != 0) { /* -1 for reserving space for terminating null-character */ 
       printf("read this %s\n", readed); 
      } 
      printf("Done reading"); 
      close(fd[0]); 
      wait(&st); /* wait for the child process to exit and release the data of the process */ 
      break; 
    } 
    return 0; /* return 0 if the execution finished successfully */ 
}