Question

Hi I want to format float numbers such that it will be displayed as follows:

decimal.fraction

where decimal = max 11 digits and
fraction = max 9 digits

and if no fraction part it should display not fraction and for more than 11 digits in decimal part representation will be in scientific form.

Can anyone help me ?

Answer 1

I don’t think there’s an internal format like this. You need to format it yourself (not tested):

void fprintf_float(FILE* f, double value) {
   if (-1e11 < value && value < 1e11) {
     double d = fabs(value);
     const char* sign = d > 0 ? "" : "-";
     double ipart, fpart;
     char fpartstr[16];
     int pos;
     fpart = modf(d, &ipart);
     snprintf(fpartstr, 16, "%.9f", fpart);
     for (pos = 10 /*strlen(fpartstr)-1*/; pos > 0; -- pos)
       if (fpartstr[pos] != '0' && fpartstr[pos] != '.')
         break;
     fpartstr[pos+1] = '\0';
     fprintf(f, "%s%.11g%s", sign, ipart, fpartstr+1);
   } else {
     fprintf(f, "%.10e", value);
   }
}