dup2 not switching to file? - c

Question

I'm trying to learn dup2 and switch the stdout to a file rather than terminal. This is the example that works everywhere but not sure why it is not working for me. I don't think I need a fork() because I don't need a different process for execute just the print statement in file.
Where function is called:
int main(int argc, char **argv){
char *something = "hello";
saveHistoryToFile(something);
}
//This is the function. There is a file names history .txt
void saveHistoryToFile(char *history){
int fw = open("history.txt",O_WRONLY | O_APPEND);
dup2(fw, 1);
printf("%s", history);
}
THE ERROR: it prints into terminal not file!

Answer 1

Your code with error checking:
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
int saveHistoryToFile(char *history);
int main(int argc, char **argv){
char *something = "hello";
if(0>saveHistoryToFile(something)) return 1;
if(0>fclose(stdout)) return perror("fclose"),-1;
}
int saveHistoryToFile(char *history){
int fw = open("history.txt",O_WRONLY | O_APPEND /*|O_CREAT, 0640*/ );
if (0>fw) return perror("open"),-1;
if (0>dup2(fw, 1)) return perror("dup2"),-1;
if (0>(printf("%s", history))) return perror("printf"),-1;
}
On a first run, I get "open: No such file or directory" because I do not have "history.txt" in my current directory.
If I add it or uncomment the O_CREAT, 0640, it runs fine on my machine.
Of course, you might run into other problems (e.g, EPERM) but the perrors should give you a hint.