Looking through the scan.l

Recently I was browsing the scan.l source code for changes since PostgreSQL 9.0 version. I always do so for new minor and major releases because I use PostgreSQL grammar in my project.

Well if you’ll look closer you may find that flex is switched to 8bit mode:

%option 8bit

But then you may find such declarations:

dolq_start [A-Za-z\200-\377_]
dolq_cont [A-Za-z\200-\377_0-9]
...
ident_start [A-Za-z\200-\377_]
ident_cont [A-Za-z\200-\377_0-9\$]
...

When I first saw these lines they blew my mind. Because from the school times I was sure that 8bit has maximum value of 255. But thanks God, there is a lot of information about flex all over internet. And suddenly, it turned out that flex uses octal notation by default. This means
'\123'
the character with octal value 123

There is also a way to use hexadecimal notation:
'\x2a'
the character with hexadecimal value 2a

So the next time you’ll see such declarations don’t be confused. So conceived! :)

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Posted in Coding

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