I am trying to write a JSON string parser in JFlex, so far I have
string = \"((\\(\"|\\|\/|b|f|n|r|t|u[0-9a-fA-F]{4})) | [^\"\\])*\"
which I thought captured the specs (http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf). I have tested it on the control characters and standard characters and symbols, but for some reason it does not accept £ or ( or ) or ¬. Please can someone let me know what is causing this behaviour?
Perhaps you are running in JLex compatability mode? If so, please see the following from the official JFlex User's Manual. It seems that it will use 7bit character codes for input by default, whereas what you want is 16bit (unicode).
You can fix this by adding the line %unicode after the first %%.
Input Character sets
%7bit
Causes the generated scanner to use an 7 bit input character set (character codes 0-127). If an input character with a code greater than 127 is encountered in an input at runtime, the scanner will throw an ArrayIndexOutofBoundsException. Not only because of this, you should consider using the %unicode directive. See also Encodings for information about character encodings. This is the default in JLex compatibility mode.
%full
%8bit
Both options cause the generated scanner to use an 8 bit input character set (character codes 0-255). If an input character with a code greater than 255 is encountered in an input at runtime, the scanner will throw an ArrayIndexOutofBoundsException. Note that even if your platform uses only one byte per character, the Unicode value of a character may still be greater than 255. If you are scanning text files, you should consider using the %unicode directive. See also section Econdings for more information about character encodings.
%unicode
%16bit
Both options cause the generated scanner to use the full Unicode input character set, including supplementary code points: 0-0x10FFFF. %unicode does not mean that the scanner will read two bytes at a time. What is read and what constitutes a character depends on the runtime platform. See also section Encodings for more information about character encodings. This is the default unless the JLex compatibility mode is used (command line option --jlex).