C / C++ / MFC

28-Jun-05 20:17

hi all!!

i am facing a problem i am bnot able to understand!!!

consider the foll codes in my project

CPrjView pview;
long c1=pview.ctr;

these r lines written in a c.cpp

and it includes the PrjView.h file

ctr is a public variable of The CPrjView class of type long

i am not underrstanding that why c1 is getting a very strange value!!!

for ef ctr is 3 and still c1 is getiing a value like -85899346

also i am not able ti change the values of variables in this c.cpp

for eg if i write

pview.ctitle="ABC";

ctitle is a public variable of CPrjView class of type CString it is giving a run time error...

please help!!!1

toxcct28-Jun-05 20:30

28-Jun-05 20:30

doing CPrjView pview; calls the default constructor CPrjView::CPrjView().

be sure you're correctly initializing ctr into this constructor, because it seems to be nowhere else getting a value...

maybe you think it contains 3, but it doesn't. did you use the debugger ?

what happens if you do the following ?

pview.ctr = 3;
long c1 = pview.ctr;

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smartymanav28-Jun-05 20:53

28-Jun-05 20:53

thanks a lot!!!!!!!!!!1

it solved my prob....i need practice!!!!!!

thanks

but can u also advice me something

i wan t to permanently save the changes made in an array of strings.....

i tried to use databse for it but cud not...do u know hot to get data from multiple tables in different variables

thanks again

toxcct28-Jun-05 20:56

28-Jun-05 20:56

what database do you use exactly ? if MS SQL Server, ADO is the best way (i consider you know about SQL though - see Carlos Antollini's ADO Classes[^] for that).

if you use simple files, it will depend on how you format them...

cheers,

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smartymanav28-Jun-05 21:02

28-Jun-05 21:02

i am using access datase linking by odbc....

is ado better???or it is possible to do so in odbs using access database

acually the thing is i am already using a database for retrieving data in a form in this same project....

i now want to use another table in the same database for retriving data in to another form

plz help or suggest a diff way

thanks

toxcct29-Jun-05 0:15

29-Jun-05 0:15

sorry, i don't know at all how to use access DB...

you should ask this in a separate thread...

(search also on codeproject && google ; there are certainly many useful articles on the subject)...

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Cool Ju29-Jun-05 23:42

Cool Ju

29-Jun-05 23:42

Hi,

U can use CDaoDatabase and CDaoRecordset Classes to handle databases. U can directly open access(.mdb) databases and also thro odbc. These classes support both of them. U can also ADO. it is better than DAO. Refer MSDN for more details.

Bye
Cool Ju Cool | :cool:

smartymanav28-Jun-05 20:57

28-Jun-05 20:57

thanks a lot
it solved my prob thanks again!!!

but can u tell me another thing

plz suggest me a medthod to permanently save the changes made during run time into a array of strings in vc++

i tried to use database but am unable as i am already using a database to get data into a form in the same project

do u know how to get data from multiple tables in the same project into diff forms...

thanks again

Christian Graus28-Jun-05 20:37

Christian Graus

28-Jun-05 20:37

smartymanav wrote:
for ef ctr is 3 and still c1 is getiing a value like -85899346

Never define a variable anywhere without giving it a default value. Otherwise, this is what you get. I think the other response covers your more specific problem.

Christian Graus - Microsoft MVP - C++

Operator= overloading

Member 341989128-Jun-05 20:01

28-Jun-05 20:01

How to get such a kind of operator= overloading that given a class instance we will be able to do this

class Test
{
int m_data[10][10];
public:
void operator=(int x);
};

Test tst;
tst(2,3) = 20; //and that 20 number will be put to m_data[2][3] ?

9ine

Re: Operator= overloading [edited - bis]

Christian Graus28-Jun-05 20:06

Christian Graus

28-Jun-05 20:06

You can't, at least I don't think so.

Christian Graus - Microsoft MVP - C++

toxcct28-Jun-05 20:23

28-Jun-05 20:23

i don't understand you're problem...

you want to overload the operator=() for your class Test ?

nop, it's not actually what you want. here, you need an operator=() that returns an int. right ?
but what you can't do is reaching the (2,3) cell in your array.
so, you have to overload the operator()()...

<font color=blue>class</font> Test {
    <font color=blue>int</font> m_data[10][10];
 
  <font color=blue>public</font>:
    Test();
    <font color=blue>virtual </font>~Test();
    <font color=blue>void operator</font>=(<font color=blue>int</font>);    <font color=green>// not needed anymore</font>
    <font color=blue>int</font>& <font color=blue>operator</font>()(<font color=blue>int</font> x, <font color=blue>int</font> y);
};
 
<font color=blue>int</font>& Test::<font color=blue>operator</font>()(<font color=blue>int</font> x, <font color=blue>int</font> y) {
    <font color=green>// Tests if the indexes are in the ranges...</font>
    <font color=blue>if</font> (x <  0) x =  0;
    <font color=blue>if</font> (y <  0) y =  0;
    <font color=blue>if</font> (x > 10) x = 10;
    <font color=blue>if</font> (y < 10) y = 10;
    <font color=green>// Reaches the value...</font>
    <font color=blue>int</font>& ri = m_data[x][y];
    <font color=blue>return</font> ri;
}

this way, when you do:

Test tst;
tst(2, 3) <font color=green>// equivalent to tst.operator()(2, 3)</font>
  = 20;   <font color=green>// will use the standard operator=() working on integers</font>
ASSERT(tst(2,3) == 20);
 
Test *pTst = &tst;   <font color=green>// Pointer to tst</font>
(*pTst)(2, 3) = 21;  <font color=green>// Changes via a pointer the value of tst(2, 3)</font>
ASSERT(tst(2,3) == 21);

cheers,

TOXCCT >>> GEII power
[toxcct][VisualCalc]

Cedric Moonen28-Jun-05 20:31

Cedric Moonen

28-Jun-05 20:31

It is not the = operator that you need to overload but rather the [] operator. But in your case you have two nestled [] operators so you will need to make use of an intermediate class (like RowTest).
Something like that:

<br />
class RowTest<br />
{<br />
int m_data[10];<br />
public:<br />
int& operator[](int x);<br />
};<br />
<br />
<br />
class Test<br />
{<br />
RowTest m_data[10];<br />
public:<br />
RowTest& operator[](int x);<br />
};<br />

Then, by overloading this operator you will be able to do this:

Test tst;<br />
tst[2][3] = 20;

But of course there is an extra class involved. The syntax is perhaps not correct because I don't play a lot with these kind of things.

Hope this helps

toxcct28-Jun-05 20:33

28-Jun-05 20:33

nop, not the operator[]() because it can get only once value between the [ ]...

prefer operator ()()...

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Cedric Moonen28-Jun-05 20:37

Cedric Moonen

28-Jun-05 20:37

Yes, that's why you need to make use of an intermediate class... But ok, it may be a little bit too complicate. The other solutions were simplier Smile | :)

Member 341989129-Jun-05 3:52

29-Jun-05 3:52

I dont need extra class I'm going to check out of range x,y for m_data[x][y] in overloaded operator so I need that class will act as an array.
With simple array we can assign a value to it and read it:
int val;
val = m_data[x][y];
m_data[x][y] = val;

All this I want to be done by class

class Test
{
int m_data[10][10];

public:
int operator()(int x, int y);

};
int Test::operator()(int x, int y)
{
//check if x,y out of range
return m_data[y][x];
}

1. so we can read value by overloaded () operator
Test tst;
int val = tst(2,3); //which equ to val = m_data[x][y]

2. how to implement m_data[x][y] = val by Test class and what operator to overload?
if we overload just = operator then we will be able just
Test tst;
tst = 5; //but its not possible with this to provide x,y coeffs for m_data[x][y]

9ine

toxcct29-Jun-05 6:30

29-Jun-05 6:30

9ine wrote:
int Test::operator()(int x, int y)
{
//check if x,y out of range
return m_data[y][x];
}

it won't work until it returns an int (copy of the actual value... so, it is not an lvalue, an the compiler won't accept you to assign the result of the operator()().

use int& instead, as i did in my first answer[^]...

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Member 341989129-Jun-05 19:33

29-Jun-05 19:33

And how to be with class pointers?
with Test tst;
we get nice brief form:
int a = tst(3,2);
but with class pointer Test *tst1 = &tst;
we get bulky notation:
int b = tst1->operator()(3,2);
is it possible to something like tst(3,2) with pointer to class?

9ine

toxcct29-Jun-05 20:11

29-Jun-05 20:11

wohhhhh, no no no

use the defenrenciation operator...

Test *tst1 = &tst;
int b = (*tst1)(3, 2);

hope this helps you Wink | ;)

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Member 341989129-Jun-05 23:12