Problems writing some chars to files with fprintf

I'm trying to write to files with fprintf, here are some examples:

Code:

---

FILE *fp;

fp = fopen("teste.txt", "w")

fprintf(fp, "# Author: %s\n", author);

---

however, if author, for instance, has some chars like á ò ê or even €, the text file will not be saved correctly. Why?

Easy to fix? How?

works for me using VC++ 6.0

Code:

---

#include <stdio.h>

int main(int argc, char* argv[])
{
        FILE* fp = fopen("myfile.txt","w");
        fprintf(fp,"%s\n","á ò ê or even €,  ");
        fclose(fp);
        return 0;
}

---

below also works

Code:

---

        char author[] = "á ò ê or even €,  ";
        fprintf(fp,"%s\n",author);

---

After testing this a bit more I found something...
First, I'm compiling this on linux using gcc of course...

Files with special chars saved in .txt extension -> work fines, they are text files

Files with special chars saved in other extension -> file is not a text file but if I open it in a text editor I see all the text just as I see when I save it with .txt extension

Files with or without special chars -> work fine and they are text files

so the, problem is, when I save a file with those special chars with a different extension than .txt, however, I need it to be just text (and it is) but to save it in a different extension. that seems to be my problem.

When I go the file properties, I see there on the mime type: application/octet-stream instead of text/plain.

no one knows why? It would be nice if I could fix this in the next 12 hours, I'll then have to present the whole project to my teachers...