c++ LNK2001: unresolved external symbol problem - c++

Greetings.
I have searched for a solution, but I think this problem is personal code specific, hence my posting here.
I'll get straight to the point.
In my main I have two objects.
Computer *computer = new Computer();
Player *player = new Player();
In the computer class, in the header I have the following:
private:
Strategy *strategy;
int winningPosition;
int twoInRow;
int counter;
int makeTwo;
Then in Computer.cpp:
Computer::Computer(char token, bool hasTurn)
{
m_token = token;
m_hasTurn = hasTurn;
strategy = new Strategy();
}
int Computer::getMove(const char (&board)[9])
{
twoInRow = strategy->checkTwoInRow(board);
counter = strategy->counter(board);
makeTwo = strategy->makeTwo(board);
if(twoInRow != 0)
{
return twoInRow - 1;
} else if(counter != 0) {
return counter - 1;
} else if(makeTwo != 0) {
return makeTwo - 1;
} else {
return 0;
}
}
At this point I think the problem arises.
The methods called from the class Strategy all require knowledge of the board thus:
int checkTwoInRow(const char (&board)[9]);
int counter(const char (&board)[9]);
int makeTwo(const char (&board)[9]);
The problems im getting, unabling them to compile:
Error 1 error LNK2019: unresolved external symbol "public: int __thiscall Strategy::makeTwo(char const (&)[9])" (?makeTwo#Strategy##QAEHAAY08$$CBD#Z) referenced in function "public: int __thiscall Computer::getMove(char const (&)[9])" (?getMove#Computer##QAEHAAY08$$CBD#Z) C:\CPP\TTT\Computer.obj tictactoeCPP
Error 2 error LNK2019: unresolved external symbol "public: int __thiscall Strategy::counter(char const (&)[9])" (?counter#Strategy##QAEHAAY08$$CBD#Z) referenced in function "public: int __thiscall Computer::getMove(char const (&)[9])" (?getMove#Computer##QAEHAAY08$$CBD#Z) C:\CPP\TTT\Computer.obj tictactoeCPP
Error 3 error LNK2019: unresolved external symbol "public: int __thiscall Strategy::checkTwoInRow(char const (&)[9])" (?checkTwoInRow#Strategy##QAEHAAY08$$CBD#Z) referenced in function "public: int __thiscall Computer::getMove(char const (&)[9])" (?getMove#Computer##QAEHAAY08$$CBD#Z) C:\CPP\TTT\Computer.obj tictactoeCPP
As a c++ noob, I have absolutely no clue why or how this problem is caused. I think it has to do something with either the instantiation of Strategy in the computer class, or with the parameter given from computer to the strategy in the method calls.
Can anyone explain WHY this error is occuring, I don't quite understand the error at all.
And also how to solve/prevent this?
EDIT*
I just got a request to share the Strategy class:
Strategy.h:
#pragma once
class Strategy
{
public:
Strategy(void);
~Strategy(void);
int checkTwoInRow(const char (&board)[9]);
int counter(const char (&board)[9]);
int makeTwo(const char (&board)[9]);
};
The class defined these methods, I won't post them because they are quite long.

This is a linking error and it has nothing to do with instantiations or parameters.
You haven't provided the linker with the definitions for those functions. If you defined them in Strategy.cpp you need to compile that and add it as an argument to the linker. How you do that depends entirely on what tools you're using to build your program.
If you're using Visual Studio (or any other IDE) it should take care of it automatically once you've added Strategy.cpp to your project.
Or did you perhaps define them like this:
int checkTwoInRow(const char (&board)[9])
{
// Do something with board the wrong way
}
instead of like this:
int Strategy::checkTwoInRow(const char (&board)[9])
{
// Do something with board the right way
}
The first one doesn't define a Strategy member function, it defines a global function.

The error is simply stating that you have declared, but not defined, the member functions Strategy::makeTwo, Strategy::counter, and Strategy::checkTwoInRow. Are you sure that you implemented them (in a source file that's actually being compiled) and that you didn't accidentally define them as free functions?

Related

Getting "error LNK2019: unresolved external symbol ... "

I'm trying to get started with C++ but I keep getting this error. I know which parts of my code is generating it, but I think that at least one these parts shouldn't generate them.
I am creating a class called Text that is functioning in a way similar to the std::string class, just to experiment and get a better understanding of value semantics.
Anyhow, these are my files:
Text.h:
#ifndef TEXT
#define TEXT
class Text {
public:
Text(const char *str);
Text(const Text& other);
void operator=(const Text& other);
~Text();
private:
int size;
char* cptr;
};
#endif
Text.cpp:
#include "Text.h"
#include <cstring>
#include <iostream>
using namespace std;
Text::Text(const char* str) {
size = strlen(str) + 1;
cptr = new char[size];
strcpy(cptr, str);
}
Text::Text(const Text& other) {
size = other.size;
cptr = new char[size];
strcpy(cptr, str);
}
void Text::operator=(const Text& other){
delete [] cptr;
size = other.size;
cptr = new char[size];
strcpy(cptr, other.ctpr);
}
Text::~Text() {
delete [] cptr;
}
Main.cpp:
#include <iostream>
#include "Text.h"
using namespace std;
Text funk(Text t) {
// ...
return t;
}
int main() {
Text name("Mark");
Text name2("Knopfler");
name = funk(name);
name = name2;
return 0;
}
So what's causing the error is the function funk, and the first two lines in the main function. I get why it's complaining on the first two lines in the main function, because there are no function called "name" or "name2". But what I'm trying to do is declaring and initialize an object in one line (I'm and old Java guy :p), is this even possible in C++? I can't find anything online indicating this.
The funny thing is that this code is more or less copied from some code my lecturer executes just fine during a lecture. And he has certainly not declared any functions named "name" and "name2" either. Any reasonable explanation for this?
But why is the function funk generating this error as well? All I am doing is returning a copy of the object that I'm sending in.
Thanks in advance!
Edit: Here comes the full error messages. There are five of them. "SecondApplication" is the name of my project.
Error 1 error LNK2019: unresolved external symbol "public: __thiscall Text::Text(char const *)" (??0Text##QAE#PBD#Z) referenced in function _main C:\Users\XXX\Documents\Visual Studio 2013\Projects\SecondApplication\SecondApplication.obj SecondApplication
Error 2 error LNK2019: unresolved external symbol "public: __thiscall Text::Text(class Text const &)" (??0Text##QAE#ABV0##Z) referenced in function "class Text __cdecl funk(class Text)" (?funk##YA?AVText##V1##Z) C:\Users\XXX\Documents\Visual Studio 2013\Projects\SecondApplication\SecondApplication.obj SecondApplication
Error 3 error LNK2019: unresolved external symbol "public: void __thiscall Text::operator=(class Text const &)" (??4Text##QAEXABV0##Z) referenced in function _main C:\Users\XXX\Documents\Visual Studio 2013\Projects\SecondApplication\SecondApplication.obj SecondApplication
Error 4 error LNK2019: unresolved external symbol "public: __thiscall Text::~Text(void)" (??1Text##QAE#XZ) referenced in function "class Text __cdecl funk(class Text)" (?funk##YA?AVText##V1##Z) C:\Users\XXX\Documents\Visual Studio 2013\Projects\SecondApplication\SecondApplication.obj SecondApplication
Error 5 error LNK1120: 4 unresolved externals C:\Users\XXX\Documents\Visual Studio 2013\Projects\SecondApplication\Debug\SecondApplication.exe 1 1 SecondApplication
You'll get the link errors (not compilation errors) that you see if you, for instance, forget to add "Text.cpp" to your project so it doesn't get compiled and linked.
There are two errors in the code - one is in the copy constructor, and one is in the assignment operator.
Since the compiler didn't complain about the two errors, I suspect you forgot to add the file to the project.

error LNK2019: unresolved external symbol ___iob_func referenced in function "void __cdecl Padding(int)"

Using the FTDI API compiles and links fine under Visual Studio 2012.
but under VS 2014, it gives:
Error LNK2019: unresolved external symbol ___iob_func referenced in function "void __cdecl Padding(int)"
Have the standard libraries changed?
Yes, the standard libraries have changed, and FTDI doesn't seem to care - at least not as of CDM2.12.18 driver version.
The problem is described in the answers to this question.
The void __cdecl Padding(int) function from devcon.obj within ftd2xx.lib is the culprit. It references one of stdin, stdout or stderr, given as macros. The contents of these macros changed.
Since we don't really expect any I/O from the FTDI library, we might as well provide the simplest implementation possible:
FILE* __cdecl _imp____iob_func() { return 0; }
If you want a version that does what it's supposed to do:
FILE* __cdecl _imp____iob_func()
{
struct _iobuf_VS2012 { // ...\Microsoft Visual Studio 11.0\VC\include\stdio.h #56
char *_ptr;
int _cnt;
char *_base;
int _flag;
int _file;
int _charbuf;
int _bufsiz;
char *_tmpfname; };
// VS2015 has FILE = struct {void* _Placeholder}
static struct _iobuf_VS2012 bufs[3];
static char initialized = 0;
if (!initialized) {
bufs[0]._ptr = stdin->_Placeholder;
bufs[1]._ptr = stdout->_Placeholder;
bufs[2]._ptr = stderr->_Placeholder;
initialized = 1;
}
return (FILE*)&bufs;
}

Unresolved Externals when using polymorphism

Hi i'm getting the following errors:
Error 9 error LNK1120: 2 unresolved externals
Error 8 error LNK2019: unresolved external symbol "public: virtual __thiscall physics::~physics(void)" (??1physics##UAE#XZ) referenced in function "public: virtual void * __thiscall physics::`scalar deleting destructor'(unsigned int)" (??_Gphysics##UAEPAXI#Z)
Error 7 error LNK2019: unresolved external symbol "public: virtual __thiscall student::~student(void)" (??1student##UAE#XZ) referenced in function __unwindfunclet$??0physics##QAE#XZ$0
which occur using the following code:
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class student{
protected:
string fName,sName;
int id;
vector<string> cname;
vector<int> cmark;
public:
virtual ~student();
virtual void addCourse(string name, int mark)=0;
};
class physics : public student{
public:
physics(){//Initialize default values
fName="blank";
sName="blank";
id=0;
cname.push_back("none");
cmark.push_back(0);
};
~physics();
void addCourse(string name, int mark){
if(cname.size()==1){//override default value for a size of 1
cname[0]=name;
cmark[0]=mark;
}
else{
cname.push_back(name);
cmark.push_back(mark);
}
}
};
The above compiles fine but when i try to initialize an object in main() by using:
int main(){
//Database Storage
vector<student*> DB;
DB.push_back(new physics);
}
That's when i get the errors (removing the push_back line fixes it but i need this for my program). What am i doing wrong?
Turns out adding braces to the end of the destructors fixed it. What difference does that make? (from the comments)
The difference is that in one case you have a declaration which lacks a definition; in the second case you provide a (empty) definition inline.
Trying to invoke a function that is declared but not defined (as in the first case) result in an unresolved reference error raised by the linker - after all, what should it do when a function invocation is found for a function whose implementation is not available?

unresolved external symbol C++ Embedded

I have been stuck a few days now on this issue, and I cannot find an answer to my problem even though google is fuul of replies it seems like this is quite an abstract problematic.
Here is my code in H:
struct DISPLAYLINE_t {
char *text;
bool isWhite;
void set(char *txt, bool iswhite){text = txt; isWhite = iswhite;};
};
struct DISPLAY {
static DISPLAYLINE_t line1,line2,line3,line4;
void clear(){//dostuff};
};
When I try to access from my Main:
DISPLAY::line1.set(string, FALSE);
I get the following error:
error LNK2019: unresolved external symbol
"public: static struct DISPLAYLINE_t DISPLAY::line1" (?line1#DISPLAY##2UDISPLAYLINE_t##A) referenced in function WinMain
Any ideas?
You have to provide a definition at global namespace scope for your static data members (at least for those that you are odr-using in your code):
DISPLAYLINE_t DISPLAY::line1;
DISPLAYLINE_t DISPLAY::line2;
DISPLAYLINE_t DISPLAY::line3;
DISPLAYLINE_t DISPLAY::line4;
This live example shows how you should fix your program.

C++ LNK2019 error with constructors and destructors in derived classes

I have two classes, one inherited from the other. When I compile, I get the following errors:
Entity.obj : error LNK2019: unresolved external symbol "public: __thiscall Utility::Parsables::Base::Base(void)" (??0Base#Parsables#Utility##QAE#XZ) referenced in function "public: __thiscall Utility::Parsables::Entity::Entity(void)" (??0Entity#Parsables#Utility##QAE#XZ)
Entity.obj : error LNK2019: unresolved external symbol "public: virtual __thiscall Utility::Parsables::Base::~Base(void)" (??1Base#Parsables#Utility##UAE#XZ) referenced in function "public: virtual __thiscall Utility::Parsables::Entity::~Entity(void)" (??1Entity#Parsables#Utility##UAE#XZ)
D:\Programming\Projects\Caffeine\Debug\Caffeine.exe : fatal error LNK1120: 2 unresolved externals
I really can't figure out what's going on.. can anyone see what I'm doing wrong? I'm using Visual C++ Express 2008. Here are the files..
"include/Utility/Parsables/Base.hpp"
#ifndef CAFFEINE_UTILITY_PARSABLES_BASE_HPP
#define CAFFEINE_UTILITY_PARSABLES_BASE_HPP
namespace Utility
{
namespace Parsables
{
class Base
{
public:
Base( void );
virtual ~Base( void );
};
}
}
#endif //CAFFEINE_UTILITY_PARSABLES_BASE_HPP
"src/Utility/Parsables/Base.cpp"
#include "Utility/Parsables/Base.hpp"
namespace Utility
{
namespace Parsables
{
Base::Base( void )
{
}
Base::~Base( void )
{
}
}
}
"include/Utility/Parsables/Entity.hpp"
#ifndef CAFFEINE_UTILITY_PARSABLES_ENTITY_HPP
#define CAFFEINE_UTILITY_PARSABLES_ENTITY_HPP
#include "Utility/Parsables/Base.hpp"
namespace Utility
{
namespace Parsables
{
class Entity : public Base
{
public:
Entity( void );
virtual ~Entity( void );
};
}
}
#endif //CAFFEINE_UTILITY_PARSABLES_ENTITY_HPP
"src/Utility/Parsables/Entity.cpp"
#include "Utility/Parsables/Entity.hpp"
namespace Utility
{
namespace Parsables
{
Entity::Entity( void )
{
}
Entity::~Entity( void )
{
}
}
}
The relevant bit is this:
unresolved external symbol "public: __thiscall Utility::Parsables::Base::Base(void)"
You need to provide a definition for Base::Base and Base::~Base. A declaration is not good enough. Even if you have nothing to do in either function, you need to leave an empty function body, because C++ actually requires the function to exist. C++ puts things like virtual table maintenance inside your constructors and destructors, so they must be defined even if you don't need to do anything there -- C++ has to do things in there.
Are you sure Base.cpp is being included in the build?
Just encountered this exact same error today in Visual Studio 2015. Unfortunately the accepted answer didn't worked (as well as answers from many same questions). The thing that worked for me was right click on the base class cpp file, exclude and then include it again. I think somehow VS got confused while moving file around and renames and it just silently refused to compile it even though it was marked as "Included In project" = true in property editor as well as listed in vcproj file in group. This is horrible error and ended up spending good hour on it.
Either your base.cpp is not being compiled/linked or you have a misspelling in it