In C how do you redirect stdin/stdout/stderr to files when making an execvp() or similar call?

The right way to do it is to replace the file descriptors STDIN_FILENO, STDOUT_FILENO and STDERR_FILENO with the opened files using dup2(). You should also then close the original files in the child process:

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 ...}

Take a look at freopen function.

I had to do something similar with stdout and wrote two functions that do the work for me:

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);}

You can use this when stdin , stdout , stderr are terminal-

//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);