C / C++ / MFC

9-Jul-07 13:59

Hi,

I know that a constructer is not suppoused to return value, however what if my object is dependent on certin data and the constructer which lets say takes a string
as paramter finds that the data is in error is there anyway to tell this to the user of the object and maybe not create the object

Thankx

eraccn9-Jul-07 14:19

eraccn

9-Jul-07 14:19

I think u can throw a exception in your constructor

ForNow9-Jul-07 15:43

9-Jul-07 15:43

thankx

Stephen Hewitt9-Jul-07 18:06

Stephen Hewitt

9-Jul-07 18:06

If you throw an exception in the constructor the object will not be constructed and thus will not be usable.

Steve

Bram van Kampen9-Jul-07 14:31

Bram van Kampen

9-Jul-07 14:31

Constructors do not return values, but can throw exceptions. (If constructors could give an error return value, by logical extension you would have to test every constructor, which would include declarations like 'int i=0')
The YACC concept would be that the effective return value of a costructor is the object it constructs. The constructor cannot return a 'Non'object, and proceed from there, it can only succeed or fail.

So, if the string data is in error, throw an exception.

An easier method is, to separate the Construction and Initialisation process, and write a method such as Init() which CAN return Value!

LateNightsInNewry

ForNow9-Jul-07 15:42

9-Jul-07 15:42

thankx

eraccn9-Jul-07 16:53

eraccn

9-Jul-07 16:53

"http://blog.csdn.net/xiaolongzhou1225/archive/2006/09/10/1204218.aspx" will be your help

ForNow9-Jul-07 18:06

9-Jul-07 18:06

thankx

G Haranadh9-Jul-07 21:37

G Haranadh

9-Jul-07 21:37

Why dont you go for parameterized constructor instead.. Smile | :)

Use call by ref concept. Is this useful. Just pass one more argument in constructor as out parameter. retrun thru out parameter.

class CMyCls
{
public:
     CMyCls(){}
      
     CMyCls(CString str,int &nRet/*<small>This is out parameter</small>*/)
     {
         if(some thing1)
           nRet = your value; 
         else if(some thing2)
           nRet = your value; 
         else if(some thing2)
           nRet = your value; 
         else
           nRet = your value; 
     }
};
void main()
{
       <big>int result = 0;</big>
       class CMyCls obj("hello",<big>result</big>);
       //use the <big>result</big> here.
}

I dont know what you expecting. But hope this is useful 2 u.

Nice talking to you. Blush | :O

If you judge people, you have no time to love them. -- Mother Teresa

ForNow10-Jul-07 0:06

windows messages for file system [win32 api]

10-Jul-07 0:06

if the result is not what I want then I dont really need the objext created
some have suggested a Throw/exception might do the trick

Jayapal Chandran9-Jul-07 12:06

Jayapal Chandran

9-Jul-07 12:06

i want to create a hook which prevents file creation in my system... i want to prevent exe files being copied to my system. i thought i can do that by using the WM_GETMESSAGE in setwindowshookex... it works for keypress and other messages and if i know the messages for file system i can do what i thought... is it a different concept of handling the file system? hope i can get an answer from forum... if more information is needed from me i can post this again...

Re: windows messages for file system [win32 api]

eraccn9-Jul-07 14:25

eraccn

9-Jul-07 14:25

you can use api hook to hook "CreateFile" win32 api which I've invoked and find it's not stable,in IFS(Installable File System),you will use filter driver to get the creation flag and "filemon" source code will be your help.If you're interesting in such,please contract me in eraccn@gmail.com and I've got the "filemon" source code and some document about these.

Linker Error 2001

moonraker9289-Jul-07 11:23

9-Jul-07 11:23

hi all. i am trying to accomplish a very simple task but am being bogged down with a linker error that i cant resolve!!

i am making a class with an ofstream object and initializing the object is the constructor...very straightforward.

here is the code:

simpleTask.h
--------------
static ofstream dg_video; // i need static for other reasons (that shouldn't be the reason)

simpleTask.cpp constructor
---------------------------
ofstream dg_video("replay.txt", ios::out);

linker error
---------------
error LNK2001: unresolved external symbol "public: static class std::basic_ofstream<char,struct std::char_traits<char=""> > dg_scenario::dg_video" (?dg_video@dg_scenario@@2V?$basic_ofstream@DU?$char_traits@D@std@@@std@@A)
1>.\spring___Win32_Debug\spring.exe : fatal error LNK1120: 1 unresolved externals

--
dg

Mark Salsbery9-Jul-07 11:43

9-Jul-07 11:43

Static members need to be defined outside the class declaration.

In simpleTask.cpp you could add (outside of any method):

ofstream CsimpleTask::dg_video("replay.txt", ios::out);

and remove the line from the constructor (which is actually creating another automatic ofstream
variable).

Mark

Mark Salsbery
Microsoft MVP - Visual C++

This episode brought to you by the letter Z

moonraker9289-Jul-07 12:04

9-Jul-07 12:04

OK. That's progress but doesn't quite fix the problem. I am getting no linking errors but now the text that I want to print into the file is not being printed..

here is the updated source code (only the changes I've made).

line outside of any methods or constructors in simpleTask.cpp
--------------------
ofstream CsimpleTask::dg_video("replay.txt", ios::out);

lines in the constructor
--------------------
CsimpleTask::dg_video << "-- INITIAL STATE --\n\n";
CsimpleTask::dg_video << "Object: dg_bead \n";
CsimpleTask::dg_video << "position: " << bead->getCenter().x << " " << bead->getCenter().y << " " << bead->getCenter().z << "\n";
CsimpleTask::dg_video << "dynamics: " << bead->getDynamics() << "\n";
CsimpleTask::dg_video << "being_grabbed: " << bead->isBeingGrabbed() << "\n\n";
CsimpleTask::dg_video << "-- SENSOR INFORMATION --\n\n";

the stuff that I'm printing in the constructor is not shown when I view the file after running the app..

any ideas why? solutions?

--
dg

Mark Salsbery9-Jul-07 12:09

9-Jul-07 12:09

Are you actually creating a CsimpleTask object so the constructor gets called?

(I'm assuming you're referring to the CsimpleTask class constructor)

Mark

Mark Salsbery
Microsoft MVP - Visual C++

This episode brought to you by the letter Z

moonraker9289-Jul-07 12:16

9-Jul-07 12:16

Yes I am creating the object. And yes, your assumption is correct.

--
dg

Mark Salsbery9-Jul-07 12:24

9-Jul-07 12:24

Since the static object won't be destructed until the process terminates, you may need to add

CsimpleTask::dg_video.flush();

after writing to the stream.

Otherwise, something else is going on - I'd need to see the code.

Mark

Mark Salsbery
Microsoft MVP - Visual C++

This episode brought to you by the letter Z

moonraker9289-Jul-07 12:41

9-Jul-07 12:41

still doesnt work..

NOTE: the file name is simpleTask.cpp but the class name is dg_scenario...yes bad programming practice i know but i'm too lazy to change it right now Smile | :)

here is more code:

<br />
// init ofstream<br />
ofstream dg_scenario::dg_video("replay.txt", ios::out);<br />
<br />
// Constructor for the dg_scenario<br />
dg_scenario::dg_scenario(springCore* springApp, char* params) : gameBase(springApp, params)<br />
{ <br />
	// initialize the workflow that goes along with scenario if workflow is ON<br />
	if (wf) {<br />
		dg_scenario::dg_workflow = new workflow("1. Pick up the ball", 0, 0);<br />
		dg_scenario::dg_workflow->addNode("2. Move the ball to the other side", 2, 0, 1);<br />
		dg_scenario::dg_workflow->addLeft("3. You dropped the ball", 3, 0, 0);<br />
		dg_scenario::dg_workflow->addNode("4. Drop the ball on the other side", 4, 0, 0);<br />
	}<br />
	int i;<br />
    if (debug) cerr << "dg_scenario::constructor()\n";<br />
<br />
    // set the global variable: take it out, it's not clean!<br />
	{<br />
		extern ObjectArray universe;<br />
		extern SensorArray sensorarray;<br />
		extern LightArray lightarray;<br />
		this->universe = &universe;<br />
		this->sensorarray = &sensorarray;<br />
		this->lightarray = &lightarray;<br />
	}<br />
	<br />
	// sensors<br />
<br />
<br />
	// add objects to the universe<br />
<br />
	// bead<br />
	bead = universe->addObject("dg_bead"); // add object to the universe<br />
	bead->CreateSphere(5,len,-1.0); // create sphere<br />
	bead->setDiffuseColor(0.8, 0.4, 0.2, 1.0);<br />
	//bead->setTexture("dg_bead.rgb"); // texture<br />
	bead->setDynamics(Object::rigid); // make it rigid<br />
	bead->setCollisionExtent(Object::external); // set where to calc collisions<br />
	bead->Translate(-20+len,5.0,5.0); // translate all nodes<br />
	// grasper<br />
	grasper = universe->addObject("dg_grasper");<br />
	grasper->CreateForcep(9.0, 4.0);<br />
	grasper->setDiffuseColor(0.5, 0.5, 1.0, 1.0); // if textures off <br />
	grasper->setCollisionExtent(Object::external);<br />
	grasper->Translate(-20+len,10.0,5.0);<br />
	// link grasper to the sensor<br />
	//grasper->LinkToSensor(dg_sensor);<br />
	//dg_sensor->LinkToObject(grasper);<br />
	// left plane<br />
	left_plane = universe->addObject("dg_left_plane");<br />
	left_plane->CreatePlane(2*len, 2*len, 1, 1, Point3D(-20.0,0.0,0.0),'y');<br />
	left_plane->setCollisionExtent(Object::external);<br />
	left_plane->setDiffuseColor(1.0,0.0,0.0,1.0);<br />
	left_plane->setDynamics(Object::rigid);<br />
	// middle plane<br />
	middle_plane = universe->addObject("dg_middle_plane");<br />
	middle_plane->CreatePlane(2*len, len*8, 1, 1, Point3D(-20.0+2*len,0.0,0.0),'y');<br />
	middle_plane->setCollisionExtent(Object::external);<br />
	//middle_plane->setTexture("middle_plane.rgb");<br />
	middle_plane->setDiffuseColor(0.0,0.0,1.0,1.0);<br />
	middle_plane->setDynamics(Object::rigid);<br />
	// right plane<br />
	right_plane = universe->addObject("dg_right_plane");<br />
	right_plane->CreatePlane(2*len, 2*len, 1, 1, Point3D(-20.0+len*10,0.0,0.0),'y');<br />
	right_plane->setCollisionExtent(Object::external);<br />
	right_plane->setDiffuseColor(1.0,0.0,0.0,1.0);<br />
	right_plane->setDynamics(Object::rigid);<br />
	<br />
	// disable main menu<br />
	extern muiObject* main_pulldown;<br />
	//main_pulldown->visible = 0;<br />
<br />
	// not paused<br />
	extern int paused;<br />
	paused = 0;<br />
<br />
	// The camera is positioned regarding the coordinate system, not the center of<br />
	// all the objects in the scene. This way, it doesn't matter how the tools are<br />
	// positioned when the simulation starts.<br />
	extern int camera_relativ_to_univ_min_max;<br />
	camera_relativ_to_univ_min_max = 0;<br />
<br />
	// switch on collisions<br />
	springApp->setCollisionsOn(true);<br />
	springApp->setCollisionAlgorithm(springCore::AABB_CD); <br />
<br />
	// switch off gravity  (can be turned on later)<br />
	extern int do_gravity;<br />
	do_gravity = 1;<br />
	extern double gravity_floor;<br />
	gravity_floor = 0;<br />
	extern void Gravity_CB(int glui_p);<br />
	Gravity_CB(-1); // set gravity for all objects<br />
<br />
	// LIGHT 0: init default lighting<br />
	float* light_pos = lightarray->getLight(0)->getLightPos();<br />
	light_pos[0] = 0;<br />
	light_pos[1] = 1.0;<br />
	light_pos[2] = 1.0;<br />
	light_pos[3] = 0.0;<br />
<br />
	// LIGHT 1: add spotlight to be used with tools<br />
	lightarray->CreateLight();<br />
	Light* light = lightarray->getLight(1);<br />
	light->getLightPos()[3] = 1.0;   // spotlight 1=ON, 0=OFF<br />
	float* ambient_intensity = light->getAmbientIntensity();<br />
	ambient_intensity[0] = 1.0;<br />
	ambient_intensity[1] = 1.0;<br />
	ambient_intensity[2] = 1.0;<br />
	ambient_intensity[3] = 0.0;<br />
	float* diffuse_intensity = light->getDiffuseIntensity();<br />
	diffuse_intensity[0] = 1.0;<br />
	diffuse_intensity[1] = 1.0;<br />
	diffuse_intensity[2] = 1.0;<br />
	diffuse_intensity[3] = 1.0;<br />
	float* specular_intensity = light->getSpecularIntensity();<br />
	specular_intensity[0] = 1.0;<br />
	specular_intensity[1] = 1.0;<br />
	specular_intensity[2] = 1.0;<br />
	specular_intensity[3] = 0.0;<br />
	light->setAttenuationConstant(0);<br />
	light->setAttenuationLinear(0);<br />
	light->setAttenuationQuadratic(0.01);<br />
	light->setSpotExponent(128);<br />
	light->setSpotCutoff(180);<br />
<br />
	// set fullscreen<br />
	extern void windowsize_submenu_fn(int ItemNo);<br />
	//windowsize_submenu_fn(7);		// 7=full screen<br />
	isDone = false; <br />
<br />
	// video initializations<br />
	dg_scenario::dg_video << "-- INITIAL STATE --\n\n";<br />
	dg_scenario::dg_video << "Object: dg_bead \n";<br />
	dg_scenario::dg_video << "position: " << bead->getCenter().x << " " << bead->getCenter().y << " " << bead->getCenter().z << "\n";<br />
	dg_scenario::dg_video << "dynamics: " << bead->getDynamics() << "\n";<br />
	dg_scenario::dg_video << "being_grabbed: " << bead->isBeingGrabbed() << "\n\n";<br />
	dg_scenario::dg_video << "-- SENSOR INFORMATION --\n\n";<br />
}<br />
<br />
// Cleans up the dg_scenario, i.e. removes it from memory<br />
dg_scenario::~dg_scenario() <br />
{ <br />
    if (debug) cerr << "dg_scenario::destructor()\n";<br />
	dg_scenario::dg_video.flush();<br />
	dg_scenario::dg_video.close();<br />
}<br />
<br />
// static update function<br />
void dg_scenario::update_video_file(Point3D spt, int oc)<br />
{<br />
	dg_scenario::dg_video << "position: " << spt.x << " " << spt.y << " " << spt.z << "\n";<br />
	dg_scenario::dg_video << "state: " << oc << "\n\n";<br />
}

--
dg

Mark Salsbery9-Jul-07 12:56

9-Jul-07 12:56

I don't see anything...

Are you at least getting an empty replay.txt file when you exit the app or the dg_scenario
destructor is called (actually it should exist as soon as the

ofstream dg_scenario::dg_video<br />
("replay.txt", ios::out);

line is executed at startup)?

If you put a breakpoint on

ofstream dg_scenario::dg_video("replay.txt", ios::out);

and run the app, is dg_scenario::dg_video constructed properly?

I'm not sure what's going on - I'm testing here with equivalent code and it works fine. Confused | :confused:

Mark

Mark Salsbery
Microsoft MVP - Visual C++

This episode brought to you by the letter Z

Mark Salsbery9-Jul-07 13:04

9-Jul-07 13:04

Also, if you add a flush call to the constructor after the last text is written
so it looks like this:

dg_scenario::dg_video << "-- SENSOR INFORMATION --\n\n";<br />
dg_scenario::dg_video.flush();

and put a breakpoint on the line calling flush(), the replay.txt file should have text in it
after flush is called.

If you're not seeing any "replay.txt" file at all, then you may want to specify a path with the
name so you can find it Smile | :)

Mark

Mark Salsbery
Microsoft MVP - Visual C++

This episode brought to you by the letter Z

moonraker9289-Jul-07 13:17

9-Jul-07 13:17

OK. I put a breakpoint on the line in the constructor which enters the first line of text and added the flush() at the end of the constructor. I stepped through all the lines and after passing flush(), opened the replay.txt file. The text had been entered successfully!!

HOWEVER, (after I remove that same flush() statement) if I run through the whole application, trigger the constructor and destructor, and then check the replay.txt file, I don't find anything..

any ideas why?

--
dg

Mark Salsbery9-Jul-07 13:32

9-Jul-07 13:32

moonraker928 wrote:
after passing flush(), opened the replay.txt file. The text had been entered successfully!!

Progress!

moonraker928 wrote:
HOWEVER, (after I remove that same flush() statement) if I run through the whole application, trigger the constructor and destructor, and then check the replay.txt file, I don't find anything..

Hmm...you still have a call to flush in the destructor, right?
And if you put a breakpoint there you can confirm it's getting called?

Like I mentioned, the output is buffered, so until the ofstream object is destructed (where it
flushes and closes the file) or you flush and/or close the file, your output may be sitting in a
memory buffer. Once the flush() and/or close() methods get called then there should be text in
the file.

For immediate writes to the file (while it's open) you need to call flush().

Mark

Mark Salsbery
Microsoft MVP - Visual C++

This episode brought to you by the letter Z