read bound extent record calm file

i've got calm record full annals where any domain any record bound width. initial proceed parse any record simply controlling string.substring(). there improved way?

for example, format described as:

<field1(8)><field2(16)><field3(12)>

and an instance record twin annals feeling like:

somedata0000000000123456somemoredata
data2   0000000000555555moredata    

i only wish certain i'm unaware some-more glorious proceed substring().

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update: i eventually went regex killersponge suggested:

private readonly regex relot = new regex(regex_lot, regexoptions.compiled);
const twine regex_lot = "^(?<field1>.{6})" +
                        "(?<field2>.{16})" +
                        "(?<field3>.{12})";

i following following opening fields:

match review = relot.match(record);
string field1 = match.groups["field1"].value;