I am trying to use my C++ classes for an iPhone app. I got 2 compilation errors in XCode that I do not quite understand. Here is the first one, in this header file myApps.h, I declare a class myApps and a struct PointF:
#pragma once
struct PointF {
float x;
float y;
}; // **compilation error message here :Multiple types in one declaration**
class myClass {
...
}
The second error is in a header file too,
#pragma once
class myClass1;
class myClass2;
class MyClass
{
public:
MyClass(void *view);
~MyClass();
virtual void Draw(myClass1 *c1);
//Error: Candidate is virtual void MyClass::Draw(myClass1 *)
virtual void Move(myClass2 c2[], myClass1 *c1, void *callback);
//Error: Candidate is virtual void MyClass::Move((myClass2, myClass1*, void*)
};
Thanks for your help
Ok, I don't know if this will help you but, from what I see:
myClass should have a semicolon at the end:
class myClass {
...
};
For the Candidate is virtual void MyClass::Draw(myClass1 *) below the last function of your class:
using myClass1::Draw;
using myClass1::Move;
since you probably have a method Draw and Move in myClass1... More on it here. It's hard to figure out exactly since I can't see the stuff in myClass1 and myClass2.
Just check Whether your file extension is .m or .mm for C++ files it must be .mm extension.
Related
I am trying to create a simple class in C++, but I keep getting the compilation errors:
main:2: error: variable or field 'doSomething' declared void
main:2: error: 'person' was not declared in this scope
main:
class person {
public:
int a;
};
void doSomething(person joe) {
return;
}
main() and stuff would go here, but even if I include main(){}, the errors still occur. I also tried adding 2 closed parentheses after joe, but then that creates the error:
main: In function 'void doSomething(person (*)())':
main:8: error: request for member 'a' in 'joe', which is of non-class type 'person (*)()'
Any help is greatly appreciated. (I hope this isn't something really stupid I'm missing, because I've been researching for hours).
Edit: I found out this is an Arduino-specific error. This post answers it.
I found out after reading this post that a way to work around this is:
typedef struct person{
public:
int a;
};
void doSomething(void *ptr)
{
person *x;
joe = (person *)ptr;
joe->a = 3; //To set a to 3
//Everything else is normal, except changing any value of person uses "->" rather than "."
return;
}
main()
{
person larry;
doSomething(&larry);
}
So essentially it is:
-Change class to typedef struct
-in the parameter, replace newtype with void *something
-add person *x; and x = (person *)ptr; to the beginning of the function
-whenever accessing type property, use -> rather than .
I'm not a expert but when I try to do what you want to do, I do it this way:
//create an instance of my class
MyAwesomeClass myObject;
void myFunction(MyAwesomeClass& object){
//do what you want here using "object"
object.doSomething();
object.doSomethingElse();
}
void setup() {
//setup stuff here
myObject.init();
}
void loop() {
//call myFunction this way
myFunction(myObject);
}
As I said, I'm not a C++ expert but it does the job.
Hope it helps!
My guess is, you have an invalid syntax error somewhere in the declarations above "class person...". Can you copy and paste the whole file?
I'm working on a plug-in protocol of sorts. The idea is that there's a base clase PCOperatorBase and that plugins would subclass this base class to provide specific functionality through a "process" virtual method that they override. The subclasses also should have a static struct member that hold typical plugin info: plug name, type and subtype. This info is used by another class (a PCOperatorManager) to know what types of plugins is dealing with. And I thought about having it be a static member so that there's no need to instantiate a plug to merely find out about the type of operator it is.
I have the following classes:
PCOperatorBase.h the superclass from which to derive all other plugs:
#ifdef PCOPERATORBASE_EXPORTS
#define PCOPERATORBASE_API __declspec(dllexport)
#else
#define PCOPERATORBASE_API __declspec(dllimport)
#endif
class PCOPERATORBASE_API PCOperatorBase
{
public:
typedef struct OperatorInfo
{
wchar_t* name;
wchar_t* type;
wchar_t* subtype;
} OperatorInfo;
PCOperatorBase(void);
virtual ~PCOperatorBase(void);
virtual int process(int* inBuffer, int* outBuffer, int bufferSize);
};
And then, for instance, a subclass:
BlackNWhite.h: a RGB->black / white operator -- yes, these are going to be graphics plugs, and disregard the types for the in / out buffers.. they are merely placeholders at this point.
#ifdef BLACKNWHITE_EXPORTS
#define BLACKNWHITE_API __declspec(dllexport)
#else
#define BLACKNWHITE_API __declspec(dllimport)
#endif
// This class is exported from the BlackNWhite.dll
class BLACKNWHITE_API CBlackNWhite : PCOperatorBase
{
public:
static PCOperatorBase::OperatorInfo* operatorInfo;
CBlackNWhite(void);
virtual ~CBlackNWhite(void);
//virtual int process(int* inBuffer, int* outBuffer, int bufferSize);
};
BLACKNWHITE_API CBlackNWhite* getOperatorInstance();
BLACKNWHITE_API const PCOperatorBase::OperatorInfo* getOperatorInfo();
And here the implementation file:
BlackNWhite.cpp:
#include "stdafx.h"
#include "BlackNWhite.h"
BLACKNWHITE_API CBlackNWhite* getOperatorInstance()
{
return new CBlackNWhite();
}
BLACKNWHITE_API const PCOperatorBase::OperatorInfo* getOperatorInfo()
{
return CBlackNWhite::operatorInfo;
}
CBlackNWhite::CBlackNWhite()
{
}
CBlackNWhite::~CBlackNWhite()
{
}
Now, I've tried a few approaches but I can't get the DLL to compile, because of the static member.The linker throws:
\BlackNWhite.lib and object c:\Projects\BlackNWhite\Debug\BlackNWhite.exp
1>BlackNWhite.obj : error LNK2001: unresolved external symbol "public: static struct PCOperatorBase::OperatorInfo * CBlackNWhite::operatorInfo" (?operatorInfo#CBlackNWhite##2PAUOperatorInfo#PCOperatorBase##A)
1>c:\Projects\BlackNWhite\Debug\BlackNWhite.dll : fatal error LNK1120: 1 unresolved externals
I thought that since the struct is defined inside the base class and the base class is exporting, the struct would export too. But I guess I'm wrong?
So how should I be doing it?
And regardless, is there a better approach to having the plugs' factory export their name,type and subtype without the need for instantiation than a static class member? For example, a resource file? or even another extern "C" function could return this info.. But I just felt that since it's C++ it makes the most sense to encapsulate this data (which is about the class as a factory itself) within the class, whether through a member or a method.
It doesn't have anything to do with DLLs, you declared the static member but you forgot to define it. Add this line to BlackNWhite.cpp:
PCOperatorBase::OperatorInfo* CBlackNWhite::operatorInfo = NULL;
**Edit: this only happens with llvm; gcc supports this just fine.
Consider the following.
Objective-c classes A and B.
B is a subclass of A.
We want a c++ hiearchy that looks like:
class X {
//...
public:
virtual A* getFoo();
};
class Y : public X {
//...
public:
B* getFoo();
};
However, if you do this, you'll get an error, as the Objective-c types confuse the c++ compiler:
error: virtual function 'getFoo' has a different return type ('Y *') than the function it overrides (which has return type 'X *')
I'm wondering if anyone has a workaround for this? (Obviously, long term, we'll be moving away from Objective-c classes, but that's not today).
P.S. This seems like the most similar question I could find, but I'm pretty sure it's a different problem.
This compiles and runs fine for me:
#import <Cocoa/Cocoa.h>
#interface A : NSObject
- (NSString*) bar;
#end
#implementation A
- (NSString*) bar
{
return #"";
}
#end
#interface B : A
#end
#implementation B
- (NSString*) bar
{
return #"!!!";
}
#end
class X {
//...
public:
virtual A* getFoo() = 0;
};
class Y : public X {
//...
public:
virtual B* getFoo() { return [B new]; }
};
int main (int argc, char const *argv[])
{
X* x = new Y;
NSLog(#"%#", [x->getFoo() bar]); // >> !!!
return 0;
}
Maybe your problem was that you didn't import B's header file into the file defining Y? You can't get covariance (in c++, at least) on incomplete classes, as the compiler needs to know that B inherits from A in order to compile Y.
Anyway, to answer your question, looks like it is possible to do this.
I recently added some openfeint code to my classes and changed them to .mm
All of a sudden I get errors that duplicate symbols are found in the object files when building.
ld: duplicate symbol _audioPlayer in blah blah /Objects-normal/i386/Stage2.o and /Users/blah blah .build/Debug-iphonesimulator/blah.build/Objects-normal/i386/Stage1.o
Why is it suddenly causing this error? What exactly is the error?
I have variables with the same name in different classes, it should be a problem?
Thanks
You're probably declaring two variables with the same name in global scope (not inside interfaces), and the linker is complaining about that.
This error can also occur if you import a .m file instead of .h.
#import "SomeClass.m"
The short answer is that you can suppress this error with a command line argument to gcc:
-Wl,--allow-multiple-definition
If you implement your method like below in .mm file, duplicate symbol errorwill occur.
#import <Foundation/Foundation.h>
class CppTestOne
{
public:
void Test();
// {
// NSLog(#"Hello C Plus Plus");
// }
};
void CppTestOne::Test()
{
NSLog(#"Hello C Plus Plus");
}
then you can implement your method by
#import <Foundation/Foundation.h>
class CppTestOne
{
public:
void Test()
{
NSLog(#"Hello C Plus Plus");
}
};
//void CppTestOne::Test()
//{
// NSLog(#"Hello C Plus Plus");
//}
more details for this error not clear
I'm trying to use class objects with the Arduino, but I keep running into problems. All I want to do is declare a class and create an object of that class. What would an example be?
On Arduino 1.0, this compiles just fine:
class A
{
public:
int x;
virtual void f() { x=1; }
};
class B : public A
{
public:
int y;
virtual void f() { x=2; }
};
A *a;
B *b;
const int TEST_PIN = 10;
void setup()
{
a=new A();
b=new B();
pinMode(TEST_PIN,OUTPUT);
}
void loop()
{
a->f();
b->f();
digitalWrite(TEST_PIN,(a->x == b->x) ? HIGH : LOW);
}
There is an excellent tutorial on how to create a library for the Arduino platform. A library is basically a class, so it should show you how its all done.
On Arduino you can use classes, but there are a few restrictions:
No new and delete keywords
No exceptions
No libstdc++, hence no standard functions, templates or classes
You also need to make new files for your classes, you can't just declare them in your main sketch. You also will need to close the Arduino IDE when recompiling a library. That is why I use Eclipse as my Arduino IDE.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1230935955 states:
By default, the Arduino IDE and
libraries does not use the operator
new and operator delete. It does
support malloc() and free(). So the
solution is to implement new and
delete operators for yourself, to use
these functions.
Code:
#include <stdlib.h> // for malloc and free
void* operator new(size_t size) { return malloc(size); }
void operator delete(void* ptr) { free(ptr); }
This let's you create objects, e.g.
C* c; // declare variable
c = new C(); // create instance of class C
c->M(); // call method M
delete(c); // free memory
Regards,
tamberg
I created this simple one a while back. The main challenge I had was to create a good build environment - a makefile that would compile and link/deploy everything without having to use the GUI. For the code, here is the header:
class AMLed
{
private:
uint8_t _ledPin;
long _turnOffTime;
public:
AMLed(uint8_t pin);
void setOn();
void setOff();
// Turn the led on for a given amount of time (relies
// on a call to check() in the main loop()).
void setOnForTime(int millis);
void check();
};
And here is the main source
AMLed::AMLed(uint8_t ledPin) : _ledPin(ledPin), _turnOffTime(0)
{
pinMode(_ledPin, OUTPUT);
}
void AMLed::setOn()
{
digitalWrite(_ledPin, HIGH);
}
void AMLed::setOff()
{
digitalWrite(_ledPin, LOW);
}
void AMLed::setOnForTime(int p_millis)
{
_turnOffTime = millis() + p_millis;
setOn();
}
void AMLed::check()
{
if (_turnOffTime != 0 && (millis() > _turnOffTime))
{
_turnOffTime = 0;
setOff();
}
}
It's more prettily formatted here: http://amkimian.blogspot.com/2009/07/trivial-led-class.html
To use, I simply do something like this in the .pde file:
#include "AM_Led.h"
#define TIME_LED 12 // The port for the LED
AMLed test(TIME_LED);
My Webduino library is all based on a C++ class that implements a web server on top of the Arduino Ethernet shield. I defined the whole class in a .h file that any Arduino code can #include. Feel free to look at the code to see how I do it... I ended up just defining it all inline because there's no real reason to separately compile objects with the Arduino IDE.
Can you provide an example of what did not work? As you likely know, the Wiring language is based on C/C++, however, not all of C++ is supported.
Whether you are allowed to create classes in the Wiring IDE, I'm not sure (my first Arduino is in the mail right now). I do know that if you wrote a C++ class, compiled it using AVR-GCC, then loaded it on your Arduino using AVRDUDE, it would work.