I decided to learn C++ DirectX, but whenever I compile/debug a code, even the simplest ones, i get the LNK2019: unresolved external symbol _WinMain# 16 referenced in function "int __cdecl_main(void)" (?invoke_main##YAHXZ) error and LNK1120.
I tested two different codes, one with class and other just int function alone:
#pragma once
class Main
{
public:
Main();
~Main();
};
Main::Main(int x)
{
}
Main::~Main()
{
}
int example()
{
return 0;
}
First and foremost you should do yourself a favour and learn C++ properly from a book. Bjarne Stroustrup, the designer and implementer of C++, has a great book which will teach you lots: Programming: Principles and Practice using C++
Your program cannot link because there is no main() function, which is required.
As Steephen has pointed out already in his answer, you can change your program so it includes at least the following:
int main()
{
return 0;
}
It looks like you were trying to substitute main() with example(), but your program and and C++ program needs to have a main(), as it's the main entry point of your program. You might also like to read http://www.cplusplus.com/doc/tutorial/program_structure/
To keep you class definition intact do following changes
Main::Main() // you don't need a parameter for your constructor
{
}
int main() //Not int example() because you need a main for your program
{
return 0;
}
Related
I am new to C++ but not to programming. I'm developing a plugin and learning the language at the same time. The plugin is for old software but still being used, so I'm using VS2015 and an SDK to match. I'm having a problem that I just don't know enough to solve but I know that it's the result of something that I'm doing wrong or don't understand. Please also consider that I'm using a third party SDK, with only .H/.HPP files and an occasional .CPP, but that's it. Everything else is wrapped in their libraries. Therefore, I don't have the liberty to change any behavior.
My code snippets are parts of their headers (can't change) and the .cpp is my modified sample code that comes along with their SDK and which I'm using as my base. It is also the area of code that causes the link error. Their samples all work, I can compile them and run them no problem. My code also works and is doing what I want. Things only break when I use my modified code. The reason I'm doing this is because I need access to the message passed into the plugin and can't find any other way to get it other than to try and override "PluginMain". The original sample code actually does call into PluginSetup.cpp because it runs other code within it as setup prior to continuing on. I've only posted the part of my code which is my attempt to override the function as I mentioned and I just included the variable declaration that causes the error. If I comment my variable declaration and other code related to it, program compiles and works again. If I move the variable declaration to another .cpp file in my codebase, code compiles no problem. It just don't like being in PluginSetup.cpp but part from maybe the main.cpp file (which I can't do anything with), PluginSetup.cpp is the first that gets called. So this is where I chose to put my override.
Am I using the friend function correctly? As you can see from the codebase, they've made the ctor as well as the friend function private.
This may also go hand in hand with a question I asked before on how to instantiate a class from this implementation using private friend function and ctors?
Hopefully, what I've posted is enough to give someone all that's needed to figure out what the problem might be.
ns1ns2Main.h
namespace ns1
{
namespace ns2
{
class Plugin;
...
}
}
extern "C" __declspec(dllexport) __MainError PluginMain(const char* caller_, const char* selector_, void* message_);
ns1ns2Plugin.h
#include "ns1ns2Main.h"
namespace ns1
{
namespace ns2
{
class Plugin
{
Public:
static Plugin* const instance();
private:
friend __MainError (::PluginMain) (const char*, const char*, void*);
Plugin();
Plugin(const Plugin&);
virtual ~Plugin();
};
}
}
PluginSetup.cpp
#include "ns1ns2Main.h"
#include "ns1ns2Plugin.h"
//-> My Modification Begins
__MainError (::PluginMain) (const char* caller, const char* selector, void* message)
{
ns1::ns2::Plugin plugin;
if (!plugin.instance())
{
plugin = ns1::ns2::Plugin();
}
if (strcmp(caller, kSPInterfaceCaller) == 0)
{
if (strcmp(selector, kSPInterfaceStartupSelector) == 0)
{
bool bStatus = ns1::ns2::pluginSetup(&plugin);
if (bStatus)
{
plugin_ = clpcsx::Plugin::instance();
plugin_->startup();
}
}
else if (strcmp(selector, kSPInterfaceShutdownSelector) == 0)
{
plugin_ = clpcsx::Plugin::instance();
plugin_->shutdown();
}
}
return error;
}
//<- My Modification Ends
namespace ns1
{
namespace ns2
{
void pluginLoaded()
{
// no-op
}
bool pluginSetup(Plugin* const plugin)
{
clpcsx::Plugin::create(plugin);
plugin->setStartupCallback(NS1_NS2_CALLBACK(clpcsx::Plugin, CLPCSX_PLUG_INST, startup));
plugin->setPostStartupCallback(NS1_NS2_CALLBACK(clpcsx::Plugin, CLPCSX_PLUG_INST, postStartup));
plugin->setPreShutdownCallback(NS1_NS2_CALLBACK(clpcsx::Plugin, CLPCSX_PLUG_INST, preShutdown));
plugin->setShutdownCallback(NS1_NS2_CALLBACK(clpcsx::Plugin, CLPCSX_PLUG_INST, shutdown));
return true;
}
void pluginDestroy(Plugin* const plugin)
{
clpcsx::Plugin::destroy();
}
}
}
Link Error
1>PluginSetup.obj : error LNK2019: unresolved external symbol "private: __cdecl ns1::ns2::Plugin::Plugin(void)" (??0Plugin#ns2#ns1##AEAA#XZ) referenced in function PluginMain
You have to tell the linker to include the libraries. Since this is VS you can add to the main .cpp file
#pragma comment(lib, "xxxx.lib")
where 'xxxx.lib' is the name of the library that has those ns functions. You need to make sure they are in the VS linker path too
I use Turbo C++ and am experiencing an unexpected error in my code, please help..
I am trying to pass an array of objects to a member function.
An error : Undefined structure test , pops on the line where i define my print function
#include<iostream.h>
#include<conio.h>
class test
{
int t;
public:
void print(test T[])
{
cout<<"This Test\n";
}
};
void main()
{
clrscr();
test T1,T2[5];
T1.print(T2);
getch();
}
I have to use the outdated version of the Turbo C++ compiler at school so the syntax of the code might be different than the new compilers.
Define your function as void print(test *T).
Turbo C++ is broken in the regard of parameters of type test[] being equivalent to test*.
EDIT: I know there are similar questions, but I cannot find an answer to a following issue: Why the methods inside the class are working correctly and outside are not.
I've got a weird problem in my project which I'm developing in MSVC++ 2012. My project consists of different modules of code. The important modules from the problem's point of view is a library and the GUI. They exist as different projects in the same solution.
I have some methods in the library which are part of the classes (in this case Calibration3D):
void Calibration3D::load(const std::string &path)
I use it without problems when I need it in the GUI, however I need to use a following method (outside the class):
void xxxyyy()
But when I'm trying to use that function (outside the class but in the same namespace) I get a following error:
1>project_xml.obj : error LNK2001: unresolved external symbol "void __cdecl cci::xxxyyy(void)" (?xxxyyy#cci##YAXXZ) 1>D:\praca_pw\cci\build-msvc2012\x64\Release\\ccigui.exe : fatal error LNK1120: 1 unresolved externals
Anybody knows how to solve it?
When I have a header file like this:
namespace xyz {
void foo();
class bar { ... };
}
then I write the cpp file like this:
#include "xyz.h"
namespace xyz {
void foo() { ... }
bar::bar() { ... }
}
This means I have to type a lot less and make fewer mistakes with regard to namespaces.
OK, solved, it seems that when a method is defined inside the namespace in header file, it should also be defined explicitly as part of namespace in implementation file, in this case:
cci::xxxyyy()
{
...
}
will work and
xxxyyy()
{
...
}
will not.
I'm currently struggeling with a compilerproblem. The problem is, that i use one of the MoSync example apps called "European Countries" (written in c++) to write my own. But when i compile the modified code, it gives me following error in response:
Controller.cpp:24: Error: Unresolved symbol '__ZTVN13Flightmanager6FlightE',
I already had a look at the example several times and i already copied the code from the example to mine, but it doesn't solve any problems.
In paticutlar i might understand what the error means (i do have c experience), but i've never seen such structured error. I also looked at namespacing conventions but there shouldn't be any problems.
//Flight.h
namespace Flightmanager
{
class Flight
{
public:
static int flightCounter;
/**
* The constructor creates the user interface.
*/
Flight(char *flightnumber, char *gate, char *departure, char *additionalinfo, char *destinationairport, char *destinationairportshort) {
this->_id = flightCounter;
flightCounter ++;
this->_flightnumber = flightnumber;
this->_gate = gate;
this->_departure = departure;
this->_additionalinfo = additionalinfo;
this->_destinationairport = destinationairport;
this->_destinationairportshort = destinationairportshort;
}
virtual ~Flight();
}
//Controller.h
#include [all other includes]
#include "../Model/Flight.h"
namespace Flightmanager
{
Controller::Controller():
mFlightArray(NULL),
mCurrentlyShownScreen(NULL)
{
initScreenSizeConstants();
initPlatformType();
//error: Unresolved symbol '__TZVN13Flightmanager6FlightE'.
initData();
//error: Unresoled symbol '__TZVN13Flightmanager6Flight13flightCounterE'.
mFlightTableView = new TableViewController(*this);//error: Unresoled symbol '__TZVN13Flightmanager6Flight13flightCounterE'.
mFlightDetailView = new DetailViewController();
}
}
I use MoSync Version 3.2
Build date: 121219-1556
Thx
You need to link in something that has definitions for:
Flight::flightCounter
Flight::~Flight()
whether that's a .o object file for Flight.cpp (or some source file) or a library depends on your project.
I am fairly new to cpp but have been in c# for a while. I am trying to run a simple console application but I receive this LNK2001 error message.
I have the main.cpp, and have added another class, Zeus, with files, Zeus.h and Zeus.cpp.
Here is the main.cpp:
#include "Zeus.h"
#include <iostream>
int main()
{
Zeus::tick = 25.0;
using std::cout;
cout << "nothing";
}
Here is the Zeus.h:
static class Zeus
{
public:
static void testing(void);
public:
static double tick;
};
And here is the Zeus.cpp:
void Zeus::testing(void)
{
//Doesnt get this far
//But eventually something like
// cout << "test " << Zeus::tick;
}
And here is the error message:
Error 20 error LNK2001: unresolved external symbol "public: static double Zeus::tick"
Thanks,
You need to define Zeus::tick, typically you would to that in the in the Zeus.cpp file. You have only declared it.
double Zeus::tick = 0.0;
Also, there is no static class in C++.
As an aside, free functions can be put in namespaces, as opposed to being static functions of classes. This is the preferred way in C++, unless there are strong reasons for the function to be static.
namespace Dionysus {
void testing();
}
As the error message says: there's no definition of Zeus::tick. Add this to Zeus.cpp:
double Zeus::tick;
Oh, and in Zeus.h remove the static from
static class Zeus
In the main() function you have, what do you mean by a statement Zeus::tick = 25.0;?
Zeus is a class. So to access the individual elements of it you need to create its instance. Its just like a structure where you first create its instance to access its individual elements.
Try the following:
int main() {
Zeus myobject;
myobject.tick = 25.0;
/* Rest of the definition */
}