print double in scientific format with no integer part

Question

A simple problem but I can't get documentation about this kind of format: I want to print a float in a Fortran scientific notation, with its integer part always being zero.

 printf("%0.5E",data); // Gives 2.74600E+02

I want to print it like this:

 .27460E+03

How can I get this result as clean as possible?

Answer 1

If you only care about the integer part being 0 and not really leaving out the 0, i.e. if you're fine with 0.27460E+03 instead of .27460E+03 you could do something similar to this:

#include <stdio.h>
#include <stdlib.h>

void fortran_printf();

int main(void)
{
        double num = 274.600;
        fortran_printf(num);

        exit(EXIT_SUCCESS);
}

void fortran_printf(double num)
{
        int num_e = 0;
        while (num > 1.0) {
                num /= 10;
                num_e++;
        }

        printf("%.5fE+%02d", num, num_e);
}

Otherwise you have to take a detour over strings. Note that the code above is only meant to get you started. It certainly doesn't handle any involved cases.