Question

Regular Expressions

Write a regular expression for numeric constants in C. These are octal, decimal, or hexadecimal integers, or decimal or hexadecimal floating-point values. An octal integer begins with 0, and may contain only the digits 0-7. A hexadecimal integer begins with 0x or 0X, and may contain the digits 0-9 and a/A-f/F. A decimal floating-point value has a fractional portion (beginning with a dot) or an exponent (beginning with E or e). Unlike a decimal integer, it is allowed to start with 0. A hexadecimal floating-point value has an optional fractional portion and a mandatory exponent (beginning with P or p). In either decimal or hexadecimal, there may be digits to the left of the dot, the right of the dot, or both, and the exponent itself is given in decimal, with an optional leading + or - sign. An integer may end with an optional U or u (indicating ”unsigned”), and/or L or l (indicating ”long”) or LL or ll (indicating ”long long”). A floating-point value may end with an optional F or f (indicating ”float” – single precision) or L or l (indicating ”long” – double precision). A decimal floating point number may start with an optional + or − sign.

Answer 1

Regular Expressions for numeric constans in C.

Octal Integer
0[0-7]*([Uu](L|l|LL|ll)?|(L|l|LL|ll)[Uu]?)?

Decimal Integer
[1-9][0-9]*([Uu](L|l|LL|ll)?|(L|l|LL|ll)[Uu]?)?

Hexadecimal Integer
0[Xx][0-9a-fA-F]+([Uu](L|l|LL|ll)?|(L|l|LL|ll)[Uu]?)?

Decimal Floating point numbers
([0-9]*\.[0-9]+|[0-9]+\.)([Ee][-+]?[0-9]+)?[flFL]?[0-9]+([Ee][-+]?[0-9]+)[flFL]?

Hexa decimal Floating point numbers 
0[Xx]([0-9a-fA-F]*\.[0-9a-fA-F]+|[0-9a-fA-F]+\.?)[Pp][-+]?[0-9]+[flFL]?

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