有人能告诉我这段代码有什么问题吗?
简单来说,它创建了输入和输出管道,并分叉执行了sort
程序。父进程读取字典/usr/share/dict/words
并将其写入到管道,该管道dup2()
到sort
的标准输入中,同样地,父进程从管道中读取输出并将其打印到终端(父进程的标准输出)。或者至少应该是这样发生的。
回溯显示,父进程在第130行上的read()
处停顿(带有'XXX'注释)。就像sort
没有意识到文件末尾一样,但关闭pipeIn
的写端应该“信号”这一点,对吧?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, char** argv)
{
int pipeIn[2];
int pipeOut[2];
if ((pipe(pipeIn)) == -1)
{
perror("pipe");
exit(EXIT_FAILURE);
}
if ((pipe(pipeOut)) == -1)
{
perror("pipe");
exit(EXIT_FAILURE);
}
pid_t child = fork();
if (child == 0)
{
// This is child!
if ((dup2(pipeIn[0], STDIN_FILENO)) == -1)
{
perror("dup2");
exit(EXIT_FAILURE);
}
if ((dup2(pipeOut[1], STDOUT_FILENO)) == -1)
{
perror("dup2");
exit(EXIT_FAILURE);
}
if ((dup2(pipeOut[1], STDERR_FILENO)) == -1)
{
perror("dup2");
exit(EXIT_FAILURE);
}
if ((close(pipeIn[0])) == -1)
{
perror("close");
exit(EXIT_FAILURE);
}
if ((close(pipeOut[1])) == -1)
{
perror("close");
exit(EXIT_FAILURE);
}
if ((execlp("sort", "-r", NULL)) == -1)
{
perror("execlp");
exit(EXIT_FAILURE);
}
}
else if (child == -1)
{
perror("fork");
exit(EXIT_FAILURE);
}
else
{
// This is parent!
if ((close(pipeIn[0])) == -1)
{
perror("close");
exit(EXIT_FAILURE);
}
if ((close(pipeOut[1])) == -1)
{
perror("close");
exit(EXIT_FAILURE);
}
int dict = open("/usr/share/dict/words", O_RDONLY);
if (dict == -1)
{
perror("open");
exit(EXIT_FAILURE);
}
char buf[1024];
int count;
while ((count = read(dict, buf, sizeof(char) * 1024)) > 0)
{
putchar('.');
if ((write(pipeIn[1], buf, count)) == -1)
{
perror("write 1");
exit(EXIT_FAILURE);
}
}
if (count == -1)
{
perror("read");
exit(EXIT_FAILURE);
}
if ((close(dict)) == -1)
{
perror("close");
exit(EXIT_FAILURE);
}
if ((close(pipeIn[1])) == -1)
{
perror("close");
exit(EXIT_FAILURE);
}
while ((count = read(pipeOut[0], buf, sizeof(char) * 1024)) > 0) // XXX
{
putchar('!');
if ((write(STDOUT_FILENO, buf, count)) == -1)
{
perror("write 2");
exit(EXIT_FAILURE);
}
}
if (count == -1)
{
perror("read");
exit(EXIT_FAILURE);
}
if ((close(pipeOut[0])) == -1)
{
perror("close");
exit(EXIT_FAILURE);
}
}
return EXIT_SUCCESS;
}
感谢您的任何输入(请原谅双关语)。
sort
的标准错误发送到管道中;您应该将其保持在与调用进程的标准错误相同的位置(很可能是终端)。 - Jonathan Leffler