flex and C++

[madmaxptz]

I was trying to get a simple program to work with flex and C++. I can't figure out what's wrong though. With C it works, and I can execute yyflex() with no problems and the analyzer gets executed. With C++ on the other hand...
Take a look:

Code

%option noyywrap yylineno c++
%{
        #include <iostream>
%}
%%
"<"[A-Za-z]*">" { std::cout << YYText(); }
%%
int main () {
    yylex();
    return 0;
}

Execution

$ flex test.l
$ gcc -o test lex.yy.cc 
test.l: In function 'int main()':
test.l:10: error: 'yylex' was not declared in this scope

[horace1]

C++ needs to know the function header (name, number and type of parameters) before it can call it otherwise it gives an error message such as the one you had (in C this not an error). possibly try adding the function prototype before main()

 void     yylex(void);

[madmaxptz]

The problem was that C++ needed a FlexLexer object, and then execute the yylex() function through it.

Like this:

int main() {
        FlexLexer* lexer = new yyFlexLexer();
        while (lexer->yylex() != 0)
                ;
        return 0;
}

Solved, thanks.