cyclic dependency … how to solve?

问题

I think I have a cyclic dependency issue and have no idea how to solve it.... To be as short as possible: I am coding something like a html parser. I have a main.cpp file and two header files Parser.h and Form.h. These header files hold the whole definitions... (I'm too lazy to make the corresponding .cpp files...

Form.h looks like this:

//... standard includes like iostream....

#ifndef Form_h_included
#define Form_h_included

#include "Parser.h"
class Form {
public:
    void parse (stringstream& ss) {

        // FIXME: the following like throws compilation error: 'Parser' : is not a class or namespace name
        properties = Parser::parseTagAttributes(ss);

        string tag = Parser::getNextTag(ss);
        while (tag != "/form") {
            continue;
        }
        ss.ignore(); // >
    }
// ....
};
#endif

and Parser.h looks like this:

// STL includes
#ifndef Parser_h_included
#define Parser_h_included

#include "Form.h"

using namespace std;

class Parser {
public:
    void setHTML(string html) {
         ss << html;
    }
    vector<Form> parse() {
        vector<Form> forms;

        string tag = Parser::getNextTag(this->ss);
        while(tag != "") {
            while (tag != "form") {
                tag = Parser::getNextTag(this->ss);
            }
            Form f(this->ss);
            forms.push_back(f);
        }
    }
// ...
};
#endif

Don't know if it is important, but I'm doing the build in MS Visual Studio Ultimate 2010 and it throws me 'Parser' : is not a class or namespace name

How to solve this problem? Thank you!

回答1:

What you probably want to do here is leave the method declaration in the header like so

class Form {
public:
    void parse (stringstream& ss);
// ....
};

And define the method in a source file (i.e. a Form.cpp file) like so

#include "Form.h"
#include "Parser.h"

void parse (stringstream& ss) {

    properties = Parser::parseTagAttributes(ss);

    string tag = Parser::getNextTag(ss);
    while (tag != "/form") {
        continue;
    }
    ss.ignore(); // >
}

That should resolve the cyclic dependency issue you're seeing...

回答2:

Stop defining your member functions lexically inline in headers. Define them in source files.
Now you can take advantage of forward declarations when you need them (you don't here).

来源：https://stackoverflow.com/questions/9435666/cyclic-dependency-how-to-solve

标签

c++

dependencies

circular-dependency