Question

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Extra leading zeros when printing float using printf?

I’m trying to get the output of this C program to have placeholder zeros, as the output of this program will be used as input for another program. Right now, I’m using the following print line.

fprintf(fp1, "06 BR%d%d   %3.4f%3.4f%3.4f\n",i,d,X,Y,Z);

i = index for the loop
d = index for a second loop
X = double for a Cartesian system
Y = double for a Cartesian system
Z = double for a Cartesian system

Right now the output looks like this:

06 BR12   1.00001.00001.0000

I want it to be like the following:

06 BR0102   001.0000001.0000001.000

I know that I could just add placeholding zeros manually (if i<10, add a placeholder, etc.) but is there a more efficient way to output a placeholder zero than simply adding them in if-statements?

Thank you in advance.

Answer 1

You can zero pad with %08.4f, for example. Note that the first number is the entire field width, not just the number of places you want before the decimal. In your example, the 3 in %3.4 has no effect. If you want your last number to only have three decimal places, you’ll want %07.3f for that one.

The %d formats are easier – in your case, just %02d should do it.