dup2 redirect printf failed?
c, unix
Solution
Because stdio buffers the output, i.e. `printf("%s\n", msg)` does not immediately write to `STDOUT_FILENO`.
Add `fflush(stdout);` before redirecting stdout back.
Problem
My code is as follows: ``` #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <string.h> int main(int argc, char *argv) { int fd; int copy_stdout; char *msg = "a test message for redirect stdout"; //open a test file to write message fd = open("test", O_CREAT | O_RDWR, S_IREAD | S_IWRITE); //copy the original file descriptor copy_stdout = dup(STDOUT_FILENO); //redirect the stdout to fd dup2(fd, STDOUT_FILENO); //must close the fd to complete redirect close(fd); //write the message write(STDOUT_FILENO, msg, strlen(msg)); //redirect back dup2(copy_stdout, STDOUT_FILENO); //print the message to stdout printf("%s\n", msg); return 0; } ``` If I replace the line `write(STDOUT_FILENO, msg, strlen(msg))` with `printf("%s\n", msg)`, the program can not redirect `stdout` to file `test`, what's the reason for this?