Re: Accessing a Variable from another function. - C / C++ / MFC Discussion Boards

auralius manurung23-Sep-08 7:43

23-Sep-08 7:43

yup, i know...i meant allocating memory for s1..
my concern wasn't on part where p=s. i thought application crashed due to NULL pointer on s1...that's why we must allocate memory for s1...

Big Grin | :-D

Re: What is wrong in this strcpy()?

David Crow22-Sep-08 3:05

David Crow

22-Sep-08 3:05

I see two issues.

Member 5502879 wrote:
char * p=(char*) malloc(strlen(s));
p=s;

You've reassigned p to some other address. This will cause problems if you go to free the address returned by malloc().

Member 5502879 wrote:
strcpy(s1,p); //error, test.exe has encountered a problem

Because s1 has not been allocated any memory. strcpy() is therefore dereferencing a null pointer.

"Love people and use things, not love things and use people." - Unknown

"The brick walls are there for a reason...to stop the people who don't want it badly enough." - Randy Pausch

Re: What is wrong in this strcpy()?

Member 419459322-Sep-08 8:31

Member 4194593

22-Sep-08 8:31

Several things are wrong. As pointed out, s1 is allocated as just a pointer to a string so you cannot copy data to it. In addition, you allocated only strlen bytes for the p copy, you need to allocate strlen+1 to allow the terminating null for string s. You may get away with this if a paragraph (16 bytes) is probably allocated for the malloc, but it is still bad code.

Re: What is wrong in this strcpy()?

Mahesh Kulkarni22-Sep-08 20:34

Mahesh Kulkarni

22-Sep-08 20:34

I observed following issues
1) Issue of Memory allocation
2) this is the case where we can understand the Global an Local variable concept. Try to name ur sencond argument in list with different name. May be it will work.

The secret of life is not enjoyment
but education through experience.
- Swami Vivekananda.

Accessing a Variable from another function.

T.RATHA KRISHNAN22-Sep-08 0:19

T.RATHA KRISHNAN

22-Sep-08 0:19

Hi!
I've two functions in the same file. I've a pointer variable in the first function. I want to know the contents of this pointer variable from the second function. How to make the pointer variable visible in the second function?

Re: Accessing a Variable from another function.

CPallini22-Sep-08 0:26

CPallini

22-Sep-08 0:26

option 1 (plain C):
make the variable global (or having scope-file, declaring it static).

option 2 (C++):
if both functions are actually methods of a class, they can access class data members...

Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Re: Accessing a Variable from another function.

T.RATHA KRISHNAN22-Sep-08 0:46

T.RATHA KRISHNAN

22-Sep-08 0:46

Thanks for the reply. I can access the pointer Variable in side the second function(methods of the same class). But I want to access the contents of this pointer.
Consider the following code:

dtCore::RefPtr<dtCore::Object> m_Obj = new Object("Car");
m_Obj->LoadFile("demoMap/StaticMeshes/Pajero.IVE\0");

This is inside the first function. Here I've initialized the m_Obj variable to something. When I access this variable inside the second function it contains NULL value why because I've initialized it in the Constructor to NULL since it's a base member. But I 've to access what I've initalize in the first function from the second function not the one in the Constructor. How to do?

Re: Accessing a Variable from another function.

CPallini22-Sep-08 1:41

CPallini

22-Sep-08 1:41

Probably I didn't get you. Anyway the following simple snippet possibly may help.

class A
{
  int * _p;
public:
  A(){ _p = NULL;}
  void fun1() { _p = new int; *_p = 10; }
  void fun2() 
  {
    if (_p) 
      printf("%d\n", *_p);
    else
      printf("_p is not initialized\n");
  }
  ~A(){if (_p) delete _p;}
};

void main()
{
 A a;
 a.fun2();
 a.fun1();
 a.fun2();
}

Re: Accessing a Variable from another function.

_AnsHUMAN_ 22-Sep-08 0:27

_AnsHUMAN_

22-Sep-08 0:27

why don't you use a member variable within a class. This way you can use it across the class

Somethings seem HARD to do, until we know how to do them.
Wink | ;-)

_AnShUmAn_

Difference b/w strlen(NULL) and strlen("")

SRKSHOME22-Sep-08 0:18

SRKSHOME

22-Sep-08 0:18

Hi,
What is the difference b/w strlen(NULL) and strlen(""). strlen("") return 0 whereas strlen(NULL) crashes my program leading memory leak.Could any one explain me please?
Thanks in advance.

Re: Difference b/w strlen(NULL) and strlen("")

CPallini22-Sep-08 0:23

CPallini

22-Sep-08 0:23

"" returns a valid const char pointer to an empty string while NULL is a invalid pointer.
Smile | :)

Re: Difference b/w strlen(NULL) and strlen("")

toxcct22-Sep-08 21:30

toxcct

22-Sep-08 21:30

and why TF whould you do such a thing like strlen(NULL) ?

if you had looked at the doc before asking, you would see that strlen() gets a const char* parameter. obviously, it has to be valid (that means, it has to point to a valid string). NULL is not a valid pointer, hence the crash.

on the other hand, "" is a valid string (even though empty, but valid), so strlen("") returns the number of character in that empty string : 0 characters.

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option button in tree control

VCProgrammer21-Sep-08 23:37

VCProgrammer

21-Sep-08 23:37

Hi all,

I want to make option buttons in my tree control...

How can i do this??

thanks in advance

how to create and run a webserver in VC++(MFC)

tns_ranjith21-Sep-08 23:32

tns_ranjith

21-Sep-08 23:32

hi how to create and run a webserver in VC++(MFC)

Re: how to create and run a webserver in VC++(MFC)

Rajesh R Subramanian22-Sep-08 0:10

Rajesh R Subramanian

22-Sep-08 0:10

You just posted this same inane query 4 hours back. At first, you post a query that is not in compliance with the guidelines[^], and you can't wait for a day before re-posting it?

Many are stubborn in pursuit of the path they have chosen, few in pursuit of the goal - Friedrich Nietzsche

.·´¯`·->Rajesh<-·´¯`·.
[Microsoft MVP - Visual C++]

Re: how to create and run a webserver in VC++(MFC)

enhzflep22-Sep-08 0:36

enhzflep

22-Sep-08 0:36

There's a link to one on the front page you clown.
A C++ Embedded Web Server[^]

And yeah - I did 1 vote both posts from you asking this question today.

Re: how to create and run a webserver in VC++(MFC)

Mark Salsbery22-Sep-08 5:53

Mark Salsbery

22-Sep-08 5:53

The source code for the Apache HTTP server[^] shows a pretty good example of a web server implementation Roll eyes | :rolleyes:

Seriously, what are you asking? Do you want to use someone elses
server or develop your own? To do your own you're going to need
to have a firm grasp on the TCP/IP protocol and the HTTP protocol[^].

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

SetWindowPos don't accept values

baerten21-Sep-08 23:31

baerten

21-Sep-08 23:31

Hi everybody,

i like to center a label into a CDialog.

I calculate the left and right position of the label to set the postition via a SetWindowPos.
left gets the value of the calculation and the right value is (left + WidthOfLabel)

In this case the width of the displayed label should be constant at a width of "WidthOfLabel", right?
But in my application the width of the label grows sometimes of one pixel..
If i resize the dialog at a double size, the label has a bigger width than the initial width Sigh | :sigh:

Is there a special treatement behind the SetWindowPos which changes the sizes sometimes to fit to the Dialog automatically ?

Big thanks

Re: SetWindowPos don't accept values

SandipG 21-Sep-08 23:58

SandipG

21-Sep-08 23:58

baerten wrote:
i like to center a label into a CDialog.

You don't like CenterWindow() , do you?

Regards,
Sandip.

Re: SetWindowPos don't accept values

baerten22-Sep-08 4:23

baerten

22-Sep-08 4:23

LOL

ehm Laugh | :laugh:

Okay ... i think your way seems to be easier Big Grin | :-D

But anyway a strange behavour.

Thanks SandipG

Re: SetWindowPos don't accept values

Mark Salsbery22-Sep-08 5:37

Mark Salsbery

22-Sep-08 5:37

baerten wrote:
Is there a special treatement behind the SetWindowPos which changes the sizes sometimes to fit to the Dialog automatically ?

Not that I know of.

How are you calculating WidthOfLabel?

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Copy Byte information to structure

nitin321-Sep-08 23:29

nitin3

21-Sep-08 23:29

i have a structure and BYTE array

typedef struct _my_struct
{
DWORD dwValue ;
BYTE yValue1 ;
BYTE yValue2 ;
WORD wValue1 ;
BYTE yValue3 ;
WORD wValue2 ;
BYTE yValue4 ;
}mystruct ;

BYTE Buf[10] = {"ab--c--d"} ;

i need to copy
a to yValue1,
b to yValue2,
-- to wValue1,
c to yValue3,
-- to wValue2,
and d to yValue1.

i tried the following code but its not working

mystruct st ;
memcpy( &st.yValue1 , Buf , 6 ) ;

is any way to do that ?

Thanks & Regards

Re: Copy Byte information to structure

SandipG 21-Sep-08 23:50

SandipG

21-Sep-08 23:50