作者yueayase (scrya)
看板LinuxDev
标题[问题] dup2()的问题
时间Fri Dec 24 22:26:29 2010
以下的程式会看某执行档的输出结果是否正确,
所以用了redirect的机制:
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <fstream>
#include <iostream>
#include <string>
using namespace std;
int main()
{
pid_t pid;
int infildes, judgefildes;
string command, exename, infilename, outfilename, judgefilename;
fstream outfile, judgefile;
while(cin >> exename >> infilename >> outfilename)
{
command = "./" + exename;
judgefilename = "_" + outfilename;
judgefile.open(judgefilename.c_str(),fstream::in|fstream::out|fstream::trunc);
judgefile.close();
pid = fork();
if(pid < 0){
cerr << "fork failed\n";
return 1;
}
else if(pid == 0){
infildes = open(infilename.c_str(),O_RDONLY);
judgefildes = open(judgefilename.c_str(),O_RDWR);
/* 好奇的地方 */
close(0);
dup2(infildes,0);
close(infildes);
close(1);
dup2(judgefildes,1);
close(judgefildes);
execlp(command.c_str(),exename.c_str(),0);
}
else{
string outfile_content, judgefile_content;
/* 好奇的地方 */
outfile.open(outfilename.c_str(),fstream::in);
judgefile.open(judgefilename.c_str(),fstream::in);
while(!outfile.eof()) outfile_content += outfile.get();
while(!judgefile.eof()) judgefile_content += judgefile.get();
if(outfile_content != judgefile_content)
cout << "WRONG-ANSWER" << endl;
else
cout << "CORRECT!" << endl;
outfile.close();
judgefile.close();
}
}
return 0;
}
只是我觉得很有趣的地方是:在child process的部分用了重导,使stdout的结果
会存入档案中,那麽在parent process的地方,judgefile所要开启的档案或是
stdout的串流会不会受到child process的影响,而导致parent process的
stdout或是在开启judgefile的时候,发生一些串流的错误(找错地方)
希望能得到解答(我觉得缓冲区的buffer会被复制,所以好像不会有影响)
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