Flex + bison + Qt

[soroush]

I'm trying to generate a code for parsing a language in my Qt plain C++ project. Lexer and Parser code are working properly. I tried them separately (not in a qt project):
@
bison -d -o parser.cpp ./parser.y
flex -o lexer.cpp ./lexer.l
g++ -o ./test ./main.cpp ./lexer.cpp ./parser.cpp ./parser.hpp -lfl -m
@
Trying to add flex and bison commands to .pro by QMAKE_EXTRA_COMPILERS I'm getting 37 errors.
@
TEMPLATE = app
CONFIG += console
CONFIG -= qt

SOURCES += main.cpp
LIBS += -lfl

OTHER_FILES +=
parser.y
lexer.l

FLEXSOURCES = lexer.l
BISONSOURCES = parser.y

bison.commands = bison -o ${QMAKE_FILE_OUT} ${QMAKE_FILE_IN}
bison.input = BISONSOURCES
bison.output = parser.cpp
bison.variable_out = SOURCES
bison.name = bisonsource ${QMAKE_FILE_IN}
QMAKE_EXTRA_COMPILERS += bison

bisonheader.commands = @true
bisonheader.input = BISONSOURCES
bisonheader.output = parser.hpp
bisonheader.variable_out = HEADERS
bisonheader.name = bisonheader ${QMAKE_FILE_IN}
bisonheader.depends = parser.cpp
QMAKE_EXTRA_COMPILERS += bisonheader

flex.commands = flex -o ${QMAKE_FILE_OUT} ${QMAKE_FILE_IN}
flex.input = FLEXSOURCES
flex.output = lexer.cpp
flex.variable_out = SOURCES
flex.depends = parser.hpp
flex.name = flex ${QMAKE_FILE_IN}
QMAKE_EXTRA_COMPILERS += flex
@

errors:
@
lexer.cpp: In function 'int yylex()':
lexer.cpp:562:9: error: 'yy_init' was not declared in this scope
lexer.cpp:570:11: error: 'yy_start' was not declared in this scope
.... // and a lot of undeclared errors...
@

[pritamghanghas]

have look at qjson project, it uses bison and works for me.