Question

I have a project for school where we need to use flex and bison. I want to use C++ so that I have access to STL and my own classes that I wrote. We were provided with the following Makefile:

CC = gcc  CFLAGS = -g   OBJs = parse.tab.o symtab.o attr.o lex.yy.o   default: parser  parser: ${OBJs}     ${CC} ${CFLAGS} ${OBJs} -o parser -lfl  lex.yy.c: scan.l parse.tab.h attr.h     flex -i scan.l  parse.tab.c: parse.y attr.h symtab.h     bison -dv parse.y  parse.tab.h: parse.tab.c  clean:     rm -f parser lex.yy.c *.o parse.tab.[ch] parse.output  depend:     makedepend -I. *.c 

scan.l and parse.y have some initial flex/bison stuff to generate the scanner and parser. I need to add my own stuff to those files. symtab.{h, c} is supposed to be a implementation of a symbol table. attr.{h, c} are for some attribute magic. I want to make symtab.c a .cc file so I can use STL. I also have other reasons for wanting to use C++.

I tried to use a parse.ypp file, so that a .cpp file would be generated. But the problem is that I’m not getting the right .h file. I changed the Makefile to look like this:

CC = g++          # Change gcc to g++ CFLAGS = -g   OBJs = lex.yy.o parse.tab.o symtab.o attr.o  default: lex.yy.c parser    # added lex.yy.c so I could just keep lex stuff in C since I don't really need C++ there  parser: ${OBJs}     ${CC} ${CFLAGS} ${OBJs} -o parser -lfl  lex.yy.o: scan.l parse.tab.h attr.h      # added this rule to use gcc instead of g++     gcc -c -o lex.yy.o lex.yy.c  lex.yy.c: scan.l parse.tab.h attr.h     flex -i scan.l  parse.tab.cpp: parse.ypp attr.h symtab.h     bison -dv parse.ypp  parse.tab.h: parse.tab.cpp      # I want a parse.tab.h but I get parse.tab.hpp  clean:     rm -f parser lex.yy.c *.o parse.tab.cpp parse.tab.h parse.output  depend:     makedepend -I. *.c 

Can someone tell me what I need to add or do to get C++ working? It should be noted I added some stuff in the .y (or .ypp) file to deal with moving from C to C++. In particular, I had to declare some stuff as extern. My main problem is that when I run make, scan.l has a bunch of syntax errors, and they seem to be because it cannot include parse.tab.h (because it is never generated).

Answer 1

You don’t need to do anything with flex or bison to use C++, I have done it many times. You just have to make sure you use g++, not gcc.

Your problems are with the Makefile, not the code.