Thread: error LNK2019: unresolved external symbol

Hi everyone,

I am using a singleton class called "Slipnet" which is defined in two files: slipnet.hpp and slipnet.cpp. (relevant source code included below)

Then, I am including Slipnet.hpp in my main.cpp file and calling Slipnet::getInstance() in the main function.

I keep getting the following error:

Code:

main.obj : error LNK2019: unresolved external symbol "public: static class Slipnet * __cdecl Slipnet::getInstance(void)" (?getInstance@Slipnet@@SAPAV1@XZ) referenced in function _main
Debug/integratedApp.exe : fatal error LNK1120: 1 unresolved externals

What am I missing?

Slipnet.hpp

Code:

#ifndef SLIPNET_H
#define SLIPNET_H

#include <string>
#include "ConceptNode.hpp"
#include <map>
#include <vector>

using namespace std;


// a directed graph where each vertex represents a concept
// and each edge represents the semantic connection from one
// conept to another.  This is read from a text file that explains
// what concepts lead to what other concepts and to what degree.
// Codelets of certain type represent a concept of sorts and
// then can find themselves a node in the slipnet that matches
// their concept - from there, they know to codelets of what
// concept they can bind and they know what types of codelets to
// post to the coderack in case they manage to bind.
class Slipnet
{
    private:
		Slipnet();
		static bool instanceFlag;
		// totally static network, read once from file: /data/slip.net
		static std::map<std::string, ConceptNode*> net;
		//singleton instance.
		static Slipnet* instance;
		// facilitates traversal of the graph
		static ConceptNode* getNode(std::string type);
		// loads the file in "../../data/slip.net"
		static bool loadFile(std::string filePath);
		// helper functions to read the text file
		static bool parseChildrenAndParents(ConceptNode* node, std::string& children, std::string& parents);
		static void trim(std::string& str);
	
	public:
		static Slipnet* getInstance();
		// these functions can be called externally to get the neighbors of a given concept so that
		// new codelets can be generated accoring to the semantic slippage of ideas.
		static std::vector<std::pair < std::string, double > > getPossibleChildren(std::string codeletType);
		static std::vector<std::pair < std::string, double > > getPossibleParents(std::string codeletType);
};


#endif

Slipnet.cpp

Code:

#include "Slipnet.hpp"
#include <fstream>

using namespace std;

Slipnet* Slipnet::instance = NULL;
bool Slipnet::instanceFlag = false;
std::map<std::string, ConceptNode*> Slipnet::net;

Slipnet::Slipnet()
{
	// do nothing
}

bool Slipnet :: loadFile(std::string filePath)
// each concept node in the file is set up like this:
// concept : child1(weight), child2(weight) .. childN(weight) : parent1(weight), parent2(weight) .. parentM(weight) ;
{
	ifstream in;
	in.open(&filePath[0]);
	if(!in)
	{
		printf("error opening slipnet file not found in %s",filePath);
		return false;
	}

	std::string line;
	int lineNumber = 0;


	while(getline(in,line))
	{
		line = line.substr(0,line.find_first_of("//"));
		trim(line);
		if(line.length() == 0)
		{
			lineNumber++;
			continue;
		}
		std::string concept;
		std::string children;
		std::string parents;
		// make sure there are exactly 2 ':'s and 1 ';'s.
		int colonCounter = 0;
		int semicolonCounter = 0;
		int index = 0;
		while(index < line.length())
		{
			if(line.c_str()[index] == ':')
			{
				colonCounter++;
				if(colonCounter > 2)
				{
					printf("there can't be more than two colons in a slipnet file line, error at line %d character %d",lineNumber,index);
					in.close();
					return false;
				}
			}
			else if(line.c_str()[index] == ';')
			{
				semicolonCounter++;
				if(semicolonCounter > 1)
				{
					printf("there can't be more than one semicolon in a slipnet file line, error at line %d character %d",lineNumber,index);
					in.close();
					return false;
				}
			}
			index++;
		}
		if(colonCounter < 2)
		{
			printf("there must be exactly 2 colons in each slipnet file line, error found in line %d",lineNumber);
			in.close();
			return false;
		}
		if(semicolonCounter < 1)
		{
			printf("there must be exactly 1 semicolon in each slipnet file line, error found in line %d",lineNumber);
			in.close();
			return false;
		}
		// find 1st and 2nd colon and the semicolon.
		int indexOf1stColon = line.find_first_of(':');
		int indexOf2ndColon = line.find_first_of(':',indexOf1stColon + 1);
		int indexOfSemiColon = line.find(';');
		concept = line.substr(0,indexOf1stColon);
		trim(concept);
		// children is everything from after the first : and before the second :
		children = line.substr(indexOf1stColon+1,indexOf2ndColon - indexOf1stColon - 1);
		trim(children);
		// parents is everything after the second : and to the ';'
		parents = line.substr(indexOf2ndColon+1,indexOfSemiColon - indexOf2ndColon - 1);
		trim(parents);

		ConceptNode* node = new ConceptNode(concept);
		if(!parseChildrenAndParents(node,children,parents))
		{
			printf("error, make sure every child and parent node is followed by a parenthesized double for the weight of the link, error in line %d",lineNumber);
			in.close();
			return false;
		}
		net.insert(make_pair(concept,node));

		lineNumber++;
	}

	in.close();

	return true;
}

bool Slipnet :: parseChildrenAndParents(ConceptNode* node, std::string& children, std::string& parents)
{
	std::string helper;
	int helperIndex;
	while(children.length() > 0)
	{
		helperIndex = children.find(',');
		if(helperIndex == -1)
			helperIndex = children.length();
		helper = children.substr(0,helperIndex);
		if(helperIndex == children.length())
			children = "";
		else
			children = children.substr(helperIndex+1,children.length() - helperIndex - 1);
		trim(helper);

		// separate concept name from weight
		int indexOfParenthsStart = helper.find('(');
		int indexOfParenthsEnd =   helper.find(')');
		if(indexOfParenthsStart == -1 || indexOfParenthsEnd == -1)
			return false;
		std::string weightString = helper.substr(indexOfParenthsStart+1,indexOfParenthsEnd - indexOfParenthsStart-1);
	    helper = helper.substr(0,indexOfParenthsStart);
		trim(helper);
		double weight = atof(&weightString[0]);

		node->addChild(helper, weight);
	}
	while(parents.length() > 0)
	{
		helperIndex = parents.find(',');
		if(helperIndex == -1)
			helperIndex = parents.length();
		helper = parents.substr(0,helperIndex);
		if(helperIndex == parents.length())
			parents = "";
		else
			parents = parents.substr(helperIndex+1,parents.length() - helperIndex - 1);
		trim(helper);

		// separate concept name from weight
		int indexOfParenthsStart = helper.find('(');
		int indexOfParenthsEnd =   helper.find(')');
		if(indexOfParenthsStart == -1 || indexOfParenthsEnd == -1)
			return false;
		std::string weightString = helper.substr(indexOfParenthsStart+1,indexOfParenthsEnd - indexOfParenthsStart-1);
	    helper = helper.substr(0,indexOfParenthsStart);
		trim(helper);
		double weight = atof(&weightString[0]);

		node->addChild(helper, weight);
	}
	return true;
}

void Slipnet :: trim(std::string& str)
{
	int beginIndex = 0;
	int endIndex = str.length();
	while(str.c_str()[beginIndex] == ' ')
		beginIndex++;
	while(str.c_str()[endIndex] == ' ')
		endIndex--;
	str = str.substr(beginIndex,endIndex - beginIndex);
}

ConceptNode* Slipnet :: getNode(std::string type)
{
	std::map<std::string, ConceptNode*>::iterator it = net.find(type);
	if(it != net.end())
		return it->second;
	return NULL;
}

Slipnet* Slipnet :: getInstance()
{
    if(!instanceFlag)
	{
		instance = new Slipnet();
		instanceFlag = true;
		loadFile("../../../data/slip.net");
	}
	return instance;
}

std::vector<std::pair < std::string, double > > Slipnet :: getPossibleChildren(std::string codeletType)
{
	std::vector<std::pair < std::string, double > > answer;
	ConceptNode* node = getNode(codeletType);
	if(node != NULL)
		answer = node->getChildren();
	return answer;
}

std::vector<std::pair < std::string, double > > Slipnet :: getPossibleParents(std::string codeletType)
{
	std::vector<std::pair < std::string, double > > answer;
	ConceptNode* node = getNode(codeletType);
	if(node != NULL)
		answer = node->getParents();
	return answer;
}

main.cpp

Code:

#include "Slipnet.hpp"

using namespace std;

int main(int argc,char* argv [])
{
   Slipnet* slipnet = Slipnet::getInstance();
    .
    .
    .
    return 0;
}

Looks like you need to add Slipnet.cpp to your project.

Slipnet.hpp and Slipnet.cpp are under a project named "codelets"
main.cpp is under a separate project named "main"
Both projects are under the same solution.
I'm using Visual Studio.

Did both projects get built? codelets should be a dependent of main in the Project Dependencies. (Edit... I had this backwards originally.)

Are you linking to codelets.lib when you build the main project? I assume codelets is intended to be a static library, not a dll, is that correct?

Codelets is a static lib.
main is the "start-up" project... I don't know what you mean by project dependencies...
The codelets project gets built when I build it on its own...

Under Project > Project Dependencies, the main project depends on codelets. Checking that box allows Visual Studio to make sure changes to codelets get build before changes to main. If you build codelets manually first then that should do the same thing (although you should probably fix the dependency anyway just for your own sake). Set main as the Startup Project as well.

If you've built codelets, then a codelets.lib file should have been created, correct? Are you linking to that lib in the main project properties? Make sure the main project is selected and go to Project > Properties. Then go to Linker > Input and make sure codelets.lib is in the additional dependencies. You might also have to add the path to the codelets lib under the Additional Library Directories property of Linker > General.

That will allow the executable created when you build the main project to link to the library created by the codelets project. If you haven't done that, then you'll get the errors you indicated.

(Note that depending on which version of Visual Studio you're using, the terminology I used might be different than what you see. However, all the options should be very similar in your version. I checked VC++ 2003 for the above terms.)

<resolved>

You guys,
You were right, a quick trip into project > properties and the issue was resolved.
Thank you for your time!

</resolved>