Buffer overrun in Lexer with string literal longer than 4096 characters

[andreasabel]

The generated lexer uses a fixed buffer that can overrun when lexing a long string literal:

bnfc/source/src/BNFC/Backend/C/CFtoFlexC.hs

Lines 86 to 89 in fb85ff1

	"void YY_BUFFER_APPEND(char *s)",
	"{",
	" strcat(YY_PARSED_STRING, s); /* Do something better here! */",
	"}",

(The authors were probably aware of the problem but did not care to fix it.)
Currently the length is fixed to 4096 characters, a longer string (5000 characters) overruns the buffer, leading e.g. to a crash (C) or a parse failure (C++).
This affects the C and C++ backends.