Link C Flex lexer to C++ parser -

i using flex develop lexer language of mine. want create parser in c++ , using own approach it. since lexer in c (flex), want compile lexer (gcc -c lex.yy.c -lfl) , program (g++ -c file1.cc file2.cc ...) separately , link them create final executable.

in particular, after creating lexer, write following code c++ program:

#include <iostream>  extern int yylex(); int main(int argc, char** argv);  int main (int argc, char** argv) {   yylex();   return 0; } 

but link error when link stuff like:

g++ main.cc lex.yy.o -lfl 

but get:

/tmp/ccbrhobp.o: in function `main': main.cc:(.text+0x10): undefined reference `yylex()' collect2: ld returned 1 exit status 

where problem? thankyou

what happens here compile c code, this:

int yylex() {   // ... } 

it generates yylex symbol. compile c++ code. c++ allows 2 different functions same name exist, can't use name of function symbol name. when write int yylex(); on c++ code, gcc looks symbol: _z5yylexv. doesn't find, link error. solution c function , should use name symbol name:

#include <iostream>  extern "c" int yylex();  int main (int argc, char** argv) {   std::cout << yylex() << std::endl;   return 0; }