Difference between files written in binary and text mode

Question

What translation occurs when writing to a file that was opened in text mode that does not occur in binary mode? Specifically in MS Visual C.

unsigned char bu         


        

Answer 1

Even though this question was already answered and clearly explained, I think it would be interesting to show the main issue (translation between \n and \r\n) with a simple code example. Note that I'm not addressing the issue of the Crtl-Z character at the end of the file.

#include 
#include 

int main() {
    FILE *f;
    char string[] = "A\nB";
    int len;
    
    len = strlen(string);
    printf("As you'd expect string has %d characters... ", len); /* prints 3*/
    f = fopen("test.txt", "w"); /* Text mode */
    fwrite(string, 1, len, f);  /* On windows "A\r\nB" is writen */
    printf ("but %ld bytes were writen to file", ftell(f)); /* prints 4 on Windows, 3 on Linux*/ 
    fclose(f);
    return 0;
}

If you execute the program on Windows, you will see the following message printed:

As you'd expect string has 3 characters... but 4 bytes were writen to file

Of course you can also open the file with a text editor like Notepad++ and see yourself the characters:

The inverse conversion is performed on Windows when reading the file in text mode.