【发布时间】：2013-10-23 17:45:22
【问题描述】：
编辑：因此，通过一些额外的调试，EOF 已成功写入管道（我知道这一点，因为我进行了测试以确保 write() 函数在 produceStdin 上返回 0。 但是当 从同一个管道读取时，它说我遇到了 EOF（好）但是 EOF 元素的值等于 255（而不是像它一样的 -1通常是）。有谁知道为什么会这样？？？
我正在尝试编写这个程序，但是当我遇到来自标准输入的 EOF 时，它并没有将 -1 写入管道。无论出于何种原因，当试图通过管道传递 EOF 时，垃圾都会被写入，因此所有后续进程都会陷入无限循环。
除了在printOut() 函数中打印数组之外的所有打印语句都是我尝试调试它（由于分叉而无法使用调试器）
另外：其中一些 cmets 被回收，所以如果您看到提到“缓冲区”，那是因为 这是以前使用缓冲区而不是管道编程的。
代码如下：
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#define MAX_CHARS 81 //80 chars + null-terminator
#define NUM_CHILDREN 3
void produceStdin(int writePipe);
void child1(int readPipe, int writePipe);
void child2(int readPipe, int writePipe);
void printOut(int readPipe);
int main(int argc, char const *argv[])
{
int i,pipe1[2],pipe2[2],pipe3[2];
pid_t childPid;
if(pipe(pipe1)==-1||pipe(pipe2)==-1||pipe(pipe3)==-1)
{
fprintf(stderr, "Error in creating pipe");
}
//despite what it looks like only four children are being forked,
// all to the same parent. The children get called to their respective
//functions where they get terminated before getting to fork themselves.
for(i=0;i<NUM_CHILDREN;i++)
{
childPid=fork();
switch (childPid) {
case -1:
perror("fork() failed. Aborting.");
exit(EXIT_FAILURE);
case 0:
switch (i) {
case 0:
close(pipe1[0]); //close pipe1 read (since we're reading from stdin)
close(pipe2[0]); //close pipe2
close(pipe2[1]);
printf("right before calling stdin i=%d\n",i);
produceStdin(pipe1[1]); //write to pipe1
break;
case 1:
close(pipe1[1]); //close pipe1 write
close(pipe2[0]); //close pipe2 read
close(pipe3[0]); //close pipe3
close(pipe3[1]);
printf("right before calling child1 i=%d\n",i);
child1(pipe1[0], pipe2[1]); //read from pipe1, write to pipe2
break;
case 2:
close(pipe1[0]); //close pipe1
close(pipe1[1]);
close(pipe2[1]); //close pipe2 write
close(pipe3[0]); //close pipe3 read
printf("right before calling child2 i=%d\n",i);
child2(pipe2[0], pipe3[1]); //read from pipe2, write to pipe3
break;
default:
break;
}
default:
if(i==2)
{
close(pipe1[1]); //close pipe1
close(pipe1[0]);
close(pipe2[1]); //close pipe2
close(pipe2[0]);
close(pipe3[1]); //close pipe3 write
printOut(pipe3[0]); //read from pipe3 read
}
break;
}
}
return 0;
}
void produceStdin(int writePipe)
{
int c=0;
while(c!=EOF)
{
c=fgetc(stdin);
write(writePipe, &c, sizeof(char)); //writing EOF here is where the problem starts I believe
}
printf("Got EOF in ProdStdin\n");
printf("EOF has a value of: %d",c);
exit(0);
}
void child1(int readPipe, int writePipe)
{
int c=0;
while(c!=EOF)
{
read(readPipe,&c,sizeof(char));
// printf("Child1 got a char from pipe1: %c\n",c);
if(c=='\n')
{
c=' '; //test for newline
}
write(writePipe, &c, sizeof(char));
}
exit(0);
}
void child2(int readPipe, int writePipe)
{
int c=0;
int c2=0;
while(c!=EOF && c2!=EOF)
{
read(readPipe, &c, sizeof(char));
// printf("Child2 got a char from pipe2: %c\n",c);
if(c=='*')
{
read(readPipe, &c2, sizeof(char)); //if c is a * remove another char
if(c2=='*')
{
c='^'; //if c2 is a * then put a ^ on buffer3
write(writePipe,&c,sizeof(char));
}
else
{
write(writePipe,&c,sizeof(char));
write(writePipe,&c2,sizeof(char));
}
}
else
{
write(writePipe,&c,sizeof(char));
}
}
exit(0);
}
void printOut(int readPipe)
{
int c=0,numChars=0;
char output[MAX_CHARS];
while (c!=EOF)
{
read(readPipe, &c, sizeof(char));
// printf("PrintOut got a char from pipe3: %c\nnumChars= %d\n",c,numChars);
if (numChars==MAX_CHARS-2)
{
printf("%s\n",output);
memset(output, '\0', sizeof(char)*MAX_CHARS);
numChars=0;
}
output[numChars]=c;
numChars++;
}
printf("ABOUT TO EXIT PRINTOUT()\n");
exit(0);
}
【问题讨论】：
标签： c operating-system pipe eof