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

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 %option noyywrap yylineno c++

%{

        #include <iostream>

%}

%%

"<"[A-Za-z]*">" { std::cout << YYText(); }

%%

int main () {

    yylex();

    return 0;

}

Execution

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 $ 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()

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void yylex(void);

madmaxptz

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

Like this:

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 int main() {

        FlexLexer* lexer = new yyFlexLexer();

        while (lexer->yylex() != 0)

                ;

        return 0;

}

Solved, thanks.

flex and C++

re: flex and C++

re: flex and C++

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