C - putting current date in a filename

I have 4 values: A,B,C,D. After doing a set of computations with those values, I want my code to output the results in a file of the form ABCD_MM.DD.YY.txt, to keep track of when it was done.

I'm not quite sure on the best way to do this in C. I have a "working" version using itoa(), which isn't a standard C function and will go (and has gone) unrecognized on machines other than mine when compiling.

This is th开发者_如何学JAVAe code I have for doing this, could someone help with a better (and universally accepted) way? The char array name was defined with a global scope.

void setFileName(){  

    time_t now;

    struct tm *today;  
    char date[9];

    //get current date  
    time(&now);  
    today = localtime(&now);

    //print it in DD.MM.YY format.
    strftime(date, 15, "%d.%m.%Y", today);

    char buff[20];
    char vars[20];

    //put together a string of the form:
    //"ABCD_DD.MM.YY.txt"
    strcpy(vars, itoa(A, buff, 20));
    strcat(vars, itoa(B, buff, 20));
    strcat(vars, itoa(C, buff, 20));
    strcat(vars, itoa(D, buff, 20));

    strcpy(name, vars);
    strcat(name, "_");
    strcat(name, date);
    strcat(name, ".txt");
}

---

char filename [ FILENAME_MAX ];
snprintf(filename, FILENAME_MAX, "%d%d%d%d_%s.txt", A, B, C, D, date);