Linux 在 C 中，如何在进行 execvp() 或类似调用时将 stdin/stdout/stderr 重定向到文件？
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In C how do you redirect stdin/stdout/stderr to files when making an execvp() or similar call?
提问by Matt
I have the following code:
我有以下代码：
pid_t pid = fork();
if (pid == -1)
{
// ...
}
else if (pid == 0)
{
stdin = someopenfile;
stdout = someotherfile;
stderr = somethirdopenfile;
execvp(args[0], args);
// handle error ...
}
else
{
// ...
}
The problem is, the input/output of the execvp()call is still the console, rather than the files. Clearly I am doing something wrong, what is the right way to do this?
问题是，execvp()调用的输入/输出仍然是控制台，而不是文件。显然我做错了什么，这样做的正确方法是什么？
采纳答案by caf
The right way to do it is to replace the file descriptors STDIN_FILENO, STDOUT_FILENOand STDERR_FILENOwith the opened files using dup2(). You should also then close the original files in the child process:
正确的做法是替换文件描述符STDIN_FILENO，STDOUT_FILENO并STDERR_FILENO使用dup2(). 您还应该关闭子进程中的原始文件：
else if (pid == 0)
{
dup2(fileno(someopenfile), STDIN_FILENO);
dup2(fileno(someotherfile), STDOUT_FILENO);
dup2(fileno(somethirdopenfile), STDERR_FILENO);
fclose(someopenfile);
fclose(someotheropenfile);
fclose(somethirdopenfile);
execvp(args[0], args);
// handle error ...
}
回答by Hyman
Take a look at freopenfunction.
看看freopen功能。
I had to do something similar with stdoutand wrote two functions that do the work for me:
我不得不做类似的事情，stdout并编写了两个为我完成工作的函数：
static int fd;
static fpos_t pos;
void switchStdout(const char *newStream)
{
fflush(stdout);
fgetpos(stdout, &pos);
fd = dup(fileno(stdout));
freopen(newStream, "w", stdout);
}
void revertStdout()
{
fflush(stdout);
dup2(fd, fileno(stdout));
close(fd);
clearerr(stdout);
fsetpos(stdout, &pos);
}
回答by alhelal
You can use this when stdin , stdout , stderr are terminal-
当 stdin 、 stdout 、 stderr 是终端时，您可以使用它
//change stdin,stdout,stderr
freopen("new_stdin","r",stdin);
freopen("new_stdout","r",stdout);
freopen("new_stderr","r",stderr);
//----do something;
//reset stdin,stdout,stderr
freopen("/dev/tty","r",stdin);
freopen("/dev/tty","r",stdout);
freopen("/dev/tty","r",stderr);
