Rounding Errors in simple Range/Table output

Question

I get strange rounding errors from MachinePrecision values from Export. From this:

InputForm[Range[99.9997, 100.0003, 0.0001]]

I get:

{99.9997, 99.99980000000001, 99.99990000000001, 100., 100.0001, 100.0002, 
100.0003}

Or (and more importantly) the same happens when I want to write the values in a file (Range and Table produce the same result):

Export["test.txt", Table[x, {x, 99.9997, 100.0003, 0.0001}]]

The file test.txt contains:

99.9997
99.99980000000001
99.99990000000001
100.
100.0001
100.0002
100.00030000000001

If I try to fix this using

Export["test.txt", SetPrecision[99.99980000000001, 6]]

I get:

99.9998000000000075715433922596275806427`6.

and finally this:

Export["test.txt", N[99.99980000000001, 4]]

gives:

99.99980000000001

It sounds like a simple task but I can't figure out an elegant solution (that is not starting to build a string for example). Can you reproduce this behaviour? I'm using Mathematica 10.0.2.0. How can I get only numbers around 100 with 4 digit precision?

Answer 1

Thanks to Mr.Wizard for bringing me on the right track. Here is the shortest workaround I found using NumberForm:

Export["test.txt",Table[ToString@NumberForm[x, 7], {x, 99.9997, 100.0003, 0.0001}]];

This gives:

99.9997
99.9998
99.9999
100.
100.0001
100.0002
100.0003

Or a more general solution:

min = 99.9997; max = 100.0003; step = 0.0001;
Export["test.txt", Table[ToString@NumberForm[x, StringLength@ToString[step, InputForm] + 1] , {x, min, max, step}]];

wich gives the same but determines the precision of step automatically.