I have the following code in Visual C++:
#using <mscorlib.dll>
using namespace System;
__gc class classEx
{
public:
classEx()
{
data = "abcd";
}
classEx(String *s)
{
data=s;
}
String* getNombre()
{
return data;
}
void setNombre(String *s)
{
data=s;
}
private:
String* data;
};
int main(void)
{
classEx* obj = new classEx();
return 0;
}
I have changed the Configuration Manager to Release and Build is checked. The problem is when I try to compile it appears a bunch of errors, such as:
error C4980: '__gc' : use of this keyword requires /clr:oldSyntax command line option
cannot use this indirection on type 'System::String'
The last error points that I cannot use in the second constructor the String *s. Why is that?
Is there something that I am missing?
If you will set a corresponding compiler option to clr:oldsyntax in the project properties as the first message says, then the following code compiles without errors in Visual Studio 2010:
#include "stdafx.h"
using namespace System;
__gc class A
{
public:
A( String *s ) : data( s ) {}
String * get_data() { return data; }
private:
String *data;
};
int main()
{
A *pa = new A( "Hello World" );
Console::WriteLine( pa->get_data() );
return 0;
}
It seems that the second message is the result of that you did not set the option pointed out in the first message.
You should select menu Project → Properties → General → *Supporting of CLR (or something else because I have the Russian release of Visual Studio 2010 I can not name the option exactly in English) → clr:oldsyntax
You need to use different syntax for managed code (not the * operator):
String ^ data;
You'll also need the /clr command line option.
This article has a wealth of examples:
String (C++/CLI and C++/CX)
Related
I have this class:
class JavaScript : public QObject {
Q_OBJECT
public:
JavaScript();
bool executeFromFile(QString file);
bool enabled;
public slots:
void setEnabled( bool enabled );
bool isEnabled() const;
private:
QScriptEngine engine;
};
The methods are defined like this:
#include "javascript.h"
JavaScript::JavaScript() {
executeFromFile("test.js");
}
bool JavaScript::executeFromFile(QString file) {
QFile scriptFile(file);
if (!scriptFile.open(QIODevice::ReadOnly)) return false;
QTextStream stream(&scriptFile);
QString contents = stream.readAll();
scriptFile.close();
engine.evaluate(contents, file);
return true;
}
void JavaScript::setEnabled( bool enabled ) {
JavaScript::enabled = enabled;
}
bool JavaScript::isEnabled() const {
return enabled;
}
I’m trying to access the public slots previously defined in the header file like the documentation says:
http://doc.qt.digia.com/qt/scripting.html#making-a-c-object-available-to-scripts-written-in-qtscript
The test.js file looks like this, just like the examples of the docs:
var obj = new JavaScript();
obj.setEnabled( true );
print( "obj is enabled: " + obj.isEnabled() );
But i’m not getting anything. It seems it doesn’t find the JavaScript object. What am I missing?
Doing a simple
print(1+1)
works just fine.
EDIT: An example in the qt4 webpage implements Q_PROPERTY. I tried this, but got the same result:
Q_PROPERTY(bool enabled READ isEnabled WRITE setEnabled)
EDIT 1: Tried implementing the initializer like this:
// javascript.h:
JavaScript(QObject *parent = 0);
// javascript.cpp:
JavaScript::JavaScript(QObject *parent) : QObject(parent) {}
Still nothing...
EDIT 2: Some examples inherits from QScriptable too:
class JavaScript : public QObject, public QScriptable {}
But that makes no difference either.
You need to create QScriptClass instead of QObject. Qt contains example of how to extend script capabilites in Qt. Take a look on Custom Script Class Example
What I think you are actually missing is adding it to the script engine.
At some point you will have to declare a script engine
QScriptEngine * engine = new QScriptEngine(this);
Then you are going to want to add your object to the engine
JavaScript* js= new JavaScript();
QScriptValue jsobj = engine->newQObject(js);
engine->globalObject().setProperty("JavaScript", jsobj );
I'm by no means an expert but I think there is something else you need to do to say
var obj = new JavaScript();
at that point you probably need to take Kamil's advice and make JavaScript a subclass of QScriptClass
I want to save an alredy-existing QSettings object into some INI file for backup.
The QSettings comes from the application's global settings, ie. it can be registry, ini file, etc.
In case it helps, my context is:
class Params
{
// All params as data members
// ...
void loadGlobal ()
{
Qettings s; // Global parameters, paths set by application
// Fill data members: s.value (...);
}
};
class Algo
{
Result run (Params p)
{
Result r = F(p);
return r;
}
};
int main (...)
{
Params p;
p.loadGlobal ();
Algo a;
Result r = a.run (p);
// At this point, save Result and Params into a specific directory
// Is there a way to do:
p.saveToIni ("myparams.ini"); // <-- WRONG
}
A solution would be to add a saveTo (QSetting & s) method into the Params class:
class Params
{
void saveTo (QSettings & s)
{
s.setValue (...);
}
};
int main (...)
{
Params p;
p.loadGlobal ();
QSettings bak ("myparams.ini", ...);
p.saveTo (bak);
}
But I am looking for a solution without modifying the Params class.
Well, no, QT Doesn't really support this directly. I think your best bet is writing a helper class...something like:
void copySettings( QSettings &dst, QSettings &src )
{
QStringList keys = src.allKeys();
for( QStringList::iterator i = keys.begin(); i != keys.end(); i++ )
{
dst.setValue( *i, src.value( *i ) );
}
}
I think there are 2 issues:
QSettings does not have a copy constructor or assignment operator (that I know of), so you'll probably have to write your own copy using allKeys().
You can't save QSettings to an arbitrary file, but what you can do is set the path used for a specific format and scope using the static method QSettings::setPath(). Note that you need to do that before your backup QSettings object is created (and you would use format IniFormat).
If you're OK not having complete control over the resulting path, this should be sufficient. If not, you could still do the above, then get the file name using fileName() and use a system call to copy/move the file to the desired final location.
please help me out , why my code cannot compile,
the compiler complains that:
error C2629: 意外的“StringToAnsi (”
error C2334: “{”的前面有意外标记；跳过明显的函数体
error C2629: 意外的“StringToAnsi (”
...
Here is my code:
#using <System.dll>
#using <mscorlib.dll>
class StringToAnsi
{
private:
void * m_ptr;
public:
StringToAnsi( System::Object ^ str)
{
m_ptr = System::Runtime::InteropServices::Marshal::StringToHGlobalAnsi(safe_cast<System::String^>(str)).ToPointer();
}
StringToAnsi(System::String ^ str)
{
m_ptr = System::Runtime::InteropServices::Marshal::StringToHGlobalAnsi(str).ToPointer();
}
~StringToAnsi()
{
System::Runtime::InteropServices::Marshal::FreeHGlobal(System::IntPtr(m_ptr));
}
operator const ACHAR*()
{
return (const ACHAR*)m_ptr;
}
Because you have two constructors with the same number of parameters. There is an Object and a String, but both are an Object. So this seems very ambiguous.
When you create two methods (or constructors), you can't let them have the same number of parameters, because the compiler doesn't know which one to call.
When you put in a string into the construction like so: new StringToAnsi("bla"). The compiler doesn't know which constructor to use.
I have in an Object an QVector of Coordinates (my type) that I want to transfer to an other Vector ( I validate and than want to use ist ).
Header
bool getVector(QVector<Coordinates> &getCoordinates );
C File
static QVector<Coordinates> current;
int getVector( QVector<Coordinates> &getCoordinates)
{
.... stuff ...
getCoordinates = current;
.... stuff ....
return 0;
}
And I use it like
....
QVector<Coordinates> currentCoordinates;
getVector(currentCoordinates);
currentCoordinates.X // CRASH
The debugger goes to this line where an Live Crash happens
inline QVector(const QVector<T> &v) : d(v.d) { d->ref.ref(); if (!d->sharable) detach_helper(); }
So my how can I fix this? As I can use this to get all the other Variables with this methode.
A likely cause of your problem is that current has not been constructed before getVector is called. Initialization of static objects in C++ is a thorny area, and a frequent source of bugs - for more information, see this question, and the static initialization order fiasco FAQ entry.
A simple solution to this problem is to provide access to current via a function, i.e. replace
static QVector<Coordinates> current;
with
static QVector<Coordinates>& getCurrent()
{
static QVector<Coordinates> current;
return current;
}
Note, however, that the function as written above is not thread-safe. If multiple threads may call getCurrent, then it should be protected with a QMutex.
For gareth and the Forum :
the header:
typedef QVector<Coordinates> VesselCoordinates;
bool (*getVessel)(Charakter forCharakter, Vessel& getVessel,VesselCoordinates &getCoordinates );
later i bind tis function pointer to an static function ( cause this part of my Program will be one day convertet to c)
cpp file lower layer:
static struct {
Charakter currentPlayerVessel;
VesselCoordinates possibility;
}data;
static bool getVessel(Charakter forCharakter, Vessel& getVessel,VesselCoordinates &getCoordinates );
// funktion to bind the funktion pointer to this static funktion so it can be called outside the File
static bool serverNamespace::getVessel(Charakter forCharakter, Vessel& getVessel,VesselCoordinates &getCoordinates )
{
bool retValue= false;
if ( forCharakter == data.currentPlayerVessel){
// TODO abfragen ob die Adresse regestriert ist!
if ((true == minSize()) and ((true == shipsInRow())or (true == shipsInLine())))
{
retValue = true;
Vessel test = (Vessel)data.possibility.size();
getVessel = test;
getCoordinates = data.possibility;
}
}
return retValue;
}
And then i can use this in the upper layer cpp file to get the information i need:
// in an Funktion :
VesselCoordinates currentCoordinates;
currentCoordinates.clear();
Vessel currentVessel;
if (true == basicFleet->getVessel(currentCharakter,currentVessel, currentCoordinates ))
// doing stuff to it
so its worik fine but your idea worked just as fine. Maybe you can see why my idea is also working.
Thank you
elektor
I wrote a program to test my binary tree and when I run it, the program seems to crash (btree.exe has stopped working, Windows is checking for a solution ...).
When I ran it through my debugger and placed the breakpoint on the function I suspect is causing it, destroy_tree(), it seemed to run as expected and returned back to the main function. Main, in turn, returned from the program but then the cursor jumped back to destroy_tree() and looped recusively within itself.
The minimal code sample is below so it can be ran instantly. My compiler is MinGW and my debugger is gdb (I'm using Code::Blocks).
#include <iostream>
using namespace std;
struct node
{
int key_value;
node *left;
node *right;
};
class Btree
{
public:
Btree();
~Btree();
void insert(int key);
void destroy_tree();
private:
node *root;
void destroy_tree(node *leaf);
void insert(int key, node *leaf);
};
Btree::Btree()
{
root = NULL;
}
Btree::~Btree()
{
destroy_tree();
}
void Btree::destroy_tree()
{
destroy_tree(root);
cout<<"tree destroyed\n"<<endl;
}
void Btree::destroy_tree(node *leaf)
{
if(leaf!=NULL)
{
destroy_tree(leaf->left);
destroy_tree(leaf->right);
delete leaf;
}
}
void Btree::insert(int key, node *leaf)
{
if(key < leaf->key_value)
{
if(leaf->left!=NULL)
insert(key, leaf->left);
else
{
leaf->left = new node;
leaf->left->key_value = key;
leaf->left->left = NULL;
leaf->left->right = NULL;
}
}
else if (key >= leaf->key_value)
{
if(leaf->right!=NULL)
insert(key, leaf->right);
else
{
leaf->right = new node;
leaf->right->key_value = key;
leaf->right->left = NULL;
leaf->right->right = NULL;
}
}
}
void Btree::insert(int key)
{
if(root!=NULL)
{
insert(key, root);
}
else
{
root = new node;
root->key_value = key;
root->left = NULL;
root->right = NULL;
}
}
int main()
{
Btree tree;
int i;
tree.insert(1);
tree.destroy_tree();
return 0;
}
As an aside, I'm planning to switch from Code::Blocks built-in debugger to DDD for debugging these problems. I heard DDD can display visually pointers to objects instead of just displaying the pointer's address. Do you think making the switch will help with solving these types of problems (data structure and algorithm problems)?
Your destroy_tree() is called twice, you call it once and then it gets called after the execution leaves main() from the destructor.
You may think it should work anyway, because you check whether leaf!=NULL, but delete does not set the pointer to NULL. So your root is not NULL when destroy_tree() is called for the second time,
Not directly related (or maybe it is) to your problem, but it's good practice to give structs a constructor. For example:
struct node
{
int key_value;
node *left;
node *right;
node( int val ) : key_val( val ), left(NULL), right(NULL) {}
};
If you do this, your code becomes simpler, because you don't need worry about setting the pointers when you create a node, and it is not possible to forget to initialise them.
Regarding DDD, it;'s a fine debugger, but frankly the secret of debugging is to write correct code in the first place, so you don't have to do it. C++ gives you a lot of help in this direction (like the use of constructors), but you have to understand and use the facilities it provides.
Btree::destroy_tree doesn't set 'root' to 0 after successfully nuking the tree. As a result, the destructor class destroy_tree() again and you're trying to destroy already destroyed objects.
That'll be undefined behaviour then :).
Once you destroy the root.
Make sure it is NULL so it does not try to do it again (from the destructor)
void Btree::destroy_tree(node *leaf)
{
if(leaf!=NULL)
{
destroy_tree(leaf->left);
destroy_tree(leaf->right);
delete leaf;
leaf = NULL; // add this line
}
}