Timestamp of file in c++

i want to check a file to see if its been changed and if it is, then load it again.. for this, i started with the following code which is getting me nowhere...

#include <sys/types.h>
#include <sys/stat.h> 
#include <unistd.h>
#include <iostream>

using namespace std;

int main()
{
    struct stat st;
    int ierr = stat ("readme.txt", &st);
    if (ierr != 0) {
            cout << "error";
    }
    int date = st.st_mtime;
    while(1){
      开发者_C百科      int newdate = st.st_mtime;
            usleep(500000);
            if (newdate==date){
                    cout << "same file.. no change" << endl;
            }
            else if (newdate!=date){
                    cout << "file changed" << endl;
            }
    }
}

all the code does is print same file.. no change continuously.

---

That's because you're calling stat() outside the loop.

The result from stat() is correct at that particular moment. you need to call stat() again each time you want to check it.

---

Well, you stat before the loop. The info you obtain by your initial stat is never updated. Move the call to stat into the while loop.

---

If you are on Linux and writing specifically for that platform you can use inotify to inform you when a file changes rather than continually polling it.

See man inotify to see how to use.

---

yes you have to move stat call in while loop. your while loop should look like this

while(1){
    ierr = stat ("/Volumes/Backup/song.rtf", &st);
    int newdate = st.st_mtime;
    usleep(500000);
    if (newdate==date){
        cout << "same file.. no change" << endl;
    }
    else if (newdate!=date){
        cout << "file changed" << endl;
    }
}