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Some wired problem with floats

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Version numbers are not floating-point numbers.

The probem you're having is that the decimal value 0.09 does not have a finite binary representation. No matter whether your data file format is text or binary (though I assume it's binary) you should use integers for version numbers, for the same reason you'd use an integer for index numbers.

There are many ways to store version numbers. It's largely up to you, but you may find, for example, that two integers, for the major and minor version numbers, will be sufficient. In a binary format, you can store these as one byte each, or as the upper and lower four bits of one byte.

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Use strings. Or if you want to keep the ability to sort version numbers correctly, store it as a set of 2 or 3 integers. But you may want to pad the integers with zeroes, as something like 1.02 will come out as just 1.2. You can use the setw and setfill functions which are included with the <iomanip> header.

int v0 = 1;
int v1 = 2;
int v2 = 45;
cout << "Version: " << v0 << "." << setw(2) << setfill('0') << v1 << "." << setw(4) << v2 << endl;

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