[英]c pipes, stdin/stdout and sort
Im trying to write a program that forks and sends sort (linux) some words to sort over stdin since sort without args will use stdin. 我试图写一个程序,分叉和发送sort(linux)一些单词来排序stdin,因为没有args的排序将使用stdin。 Then collect the stdout from sort in the parent to output on parent's stdout.
然后从父级的sort中收集stdout以输出父级的stdout。
Currently my program hangs. 目前我的程序挂起了。 Could anyone lend a hand in explaining to me what is going wrong?
谁能帮我解释一下出了什么问题?
My code: 我的代码:
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
int main(int argc, char *argv[]){
int fi[2];
int fo[2];
int oldstdin;
int oldstdout;
if (pipe(fi) == -1){
exit(EXIT_FAILURE);
}
if (pipe(fo) == -1){
exit(EXIT_FAILURE);
}
oldstdin = dup(STDIN_FILENO); /* Save current sdtin */
oldstdout = dup(STDOUT_FILENO); /* Save current stdout */
close(STDIN_FILENO);
close(STDOUT_FILENO);
if(dup2 (fo[0],STDIN_FILENO) == -1) /* Make the read end of out to be stdin */
exit(EXIT_FAILURE);
if(dup2 (fi[1],STDOUT_FILENO) == -1) /* Make the write end of in to be stdout */
exit(EXIT_FAILURE);
switch(fork()){
case -1:
exit(EXIT_FAILURE);
case 0: /* CHILD */
close(fo[0]);
close(fo[1]);
close(fi[0]);
close(fi[1]);
execlp("sort","sort", (char *)NULL);
default:
break; /* fall through to parent */
}
char input[100];
close(STDIN_FILENO);
close(STDOUT_FILENO);
dup2(oldstdin,STDIN_FILENO);
dup2(oldstdout,STDOUT_FILENO);
close(fo[0]); /* these are used by CHILD */
close(fi[1]); /* "" */
write(fo[1],"dino\nbat\nfish\nzilla\nlizard\0",27);
input[read(fi[0], input,100)] = 0;
printf("%s", input);
}
I don't think sort expects stdin
to be nul-terminated: it wouldn't be if redirected from a file. 我不认为sort期望
stdin
被nul终止:如果从文件重定向则不会。
It does however need to know when the input is complete (and won't emit anything until it is, so your read will block). 但是它确实需要知道输入何时完成(并且在它输出之前不会发出任何内容,因此您的读取将被阻止)。 Try closing
fo[1]
after writing to it. 写完之后尝试关闭
fo[1]
。
Oh, and you can run this under strace -f
to see what's happening, it will show you what both parent and child processes are doing. 哦,你可以在
strace -f
下运行它来看看发生了什么,它会告诉你父进程和子进程正在做什么。
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