C / C++ / MFC

30-May-02 15:20

this is my code:

#include <iostream>

using namespace std;

char *pchar[6];
char character[6] = "hello";

int main()
{
strcpy(pchar, &character);
return 0;
}

that is "all" my code, no more no less. the problem accures on line:

strcpy(pchar, &character);

im not very sure on what this'll do, what i am trying to do is, have pchar point to the address of character. i thought that if there was more than one character i should use strcpy(), but im not very sure.

how would i accomplish this? "see any problems, or better way of doing things, just note it Smile | :)

"

Thanks!

~SilverShalkin

Paul M Watt30-May-02 16:02

Paul M Watt

30-May-02 16:02

Two problems:

1) pchar is an array of char*, not char. So you will not be able to access the elements in the pchar array as a string. Which means that you will not be able to send that array to strcpy.

What you would actually do with an array like pchar is point to 6 different strings. Then when you wanted to use one of the strings you would access the string in the array like so:

strcpy(pchar[0], ...);

2) character is a char array, which is equivalent to one char*. Therefore you do not need to take the address of the character array, you could directly pass it into strcpy like this:

strcpy(..., character);

Good Luck

Build a man a fire, and he will be warm for a day
Light a man on fire, and he will be warm for the rest of his life!

SilverShalkin30-May-02 16:18

30-May-02 16:18

but i want to point to character, if i dake the address (&) off, it wouldnt be point to character would it?

so i would have to declare my pchar like

char *pchar[6];
pchar[0] = &character[0];
pchar[1] = &character[1];
pchar[2] = &character[2];
pchar[3] = &character[3];
pchar[4] = &character[4];
pchar[5] = &character[5];

?

i hope thats wrong... thats allot to type for somthing so small Frown | :(

Thank!

~SilverShalkin

Rose | [Rose]

Roger Broomfield30-May-02 18:04

Roger Broomfield

30-May-02 18:04

Lets assume for a minute that you did do that.
You could then do this:

printf("%s\n",pchar[0]);
printf("%s\n",pchar[1]);
printf("%s\n",pchar[2]);
printf("%s\n",pchar[3]);
printf("%s\n",pchar[4]);
printf("%s\n",pchar[5]);

and the results would be:

hello
ello
llo
lo
o
<<there would="" be="" a="" blank="" line="" here="">>

in summary an array of characters IS a pointer to a sequence of characters.

so if we were to do this instead

char characters[6] = "hello";
char* pchar = characters;
char* pchars = &characters[0];

then examine the values of all three variables in the debugger.

they would all be identical.

Hope this helps in your struggle with pointers.

Roger.

Nish Nishant30-May-02 17:56

Nish Nishant

30-May-02 17:56

Do this instead :-

char *pchar;
char abc[6];

strcpy(abc,"hello");
pchar = abc;

Nish

Regards,
Nish
Native CPian.
Born and brought up on CP.
With the CP blood in him.

SilverShalkin30-May-02 18:11

30-May-02 18:11

would that work? - ill insert some of the code replies and try to understand this more... thanks guys!

Smile | :)

~SilverShalkin

Rose | [Rose]

Nish Nishant30-May-02 18:18

Nish Nishant

30-May-02 18:18

SilverShalkin wrote:
would that work?

Of course, it will work Smile | :)

Nish

Regards,
Nish
Native CPian.
Born and brought up on CP.
With the CP blood in him.

Matt Gullett30-May-02 19:55

Matt Gullett

30-May-02 19:55

WARNING: This is a long post.

I think your real problem here is a misunderstanding of how C style pointers work and how to use them. Let me start by saying that a pointer is an intrinisic data type just like float, int, char, etc. The pointer data type (on Win32 systems) is a 32 bit value. This means that when you write a statement like

void* pSomeValue;

you are telling the compiler to allocate 32 bits of memory for your program. It also identifies that you intend to populate that variable with a memory address. In the case of a void type pointer you are saying that the memory pointed to by the variable can be of any type you want. (In other words, no type affinity.)

C and C++ allows pointers to have type affinity also. This means that instead of being a void pointer, you can define a pointer like

char* pszSomeValue;

long* plSomeValue;

CSomeClassName* pSomeValue;

ETC.

When you define a pointer like this you are telling the compiler that you want it to allocate 32 bits of storabe for a variable that will eventually point to a specific data type (char, long, CSomeClassName).

The next subject of confusion (I think) is when you are using C style arrays of a particular data type. In your example, you used char* pchar[6] and char character[6] = "hello".

The char* pchar[6] is instructing the compiler to allocate 6 memory locations each having a type affinity for a pointer to a char. This means that the compiler will allocate six 32 bit memory locations whose values it expects to be pointers to a char (char*).

The char character[6] is instructing the compiler to allocate 6 memory locations each having a type affinity for a char (NOT a pointer to a char). This means that the compiler will allocate six 8 bit memory locations (that is the size of a char data type) whose value it expects to be a char.

One of the nuiansces of C style arrays is that when you allocate a C style array the compiler guarantees that the memory it allocates will be continuous. This means that when you do char *pchar[6];, the compiler is going to allocate 32*6 bits in a row. When you do char character[6], the compiler is going to allocate 8*6 bits in a row.

OK. That was a long winded explanation of pointers and arrays. With that understanding, lets look at the line of code where the compiler is giving you a problem.

strcpy(pchar, &character);

The strcpy function is defined as taking 2 paramaters, a char* and a const char*. (Ignore the const for now.) The second parameter is supposed to be a pointer to an array of characters with the last character being NULL (NULL terminated string.) The first parameter is supposed to be a pointer to an array of characters large enough to contain the data pointed to by the second parameter. (BYW strcpy will copy the contents of the second parameter to the first, therefore you will have 2 seperate copies of the data. Changing one will not affect the other.)

For the first parameter, you are passing in a an array of char* type pointers. This is quite different from an array of char type. (Remember char* = 32 bits, char = 8 bits.) As you can see, for the first parameter, the compiler is confused because it is expecting the char array, not the char* array.

You say "what i am trying to do is, have pchar point to the address of character". If this is really what you want, then what you would want to write is

char *pchar;
char character[6] = "hello";

pChar = character;

You may be thinking "how can I assign an array to a pointer?". The answer to this obvious questions goes back to the previous explanation or how C style arrays work. When you specicify the variable name of a C style array without specifying an index into the array (ie. character instead of character[0]), the compiler knows that you want a pointer to the array.

I hope this helps more that it confuses.

SilverShalkin31-May-02 11:19

Is it me, or does there seem to be a bubble of questions with long subjects and nothing of any merit in the actual body of the message.

31-May-02 11:19

it helps allot, thank you for spending the amount of time that it took to type that long thing Smile | :)

I know how pointers and stuff work, its just, there are a couple of things that are in the gray, as in (I dont know if it will do the exact thing i want it)

i guess i should use strcpy() for a pointer, "it doesnt make sense to do so Smile | :)

"

i think i should print this out... Smile | :)

Thanks for your time!

~SilverShalkin

Rose | [Rose]

Tim Smith30-May-02 13:38

Tim Smith

30-May-02 13:38

Strange...

(not picking on you redeemer)

Tim Smith

I know what you're thinking punk, you're thinking did he spell check this document? Well, to tell you the truth I kinda forgot myself in all this excitement. But being this here's CodeProject, the most powerful forums in the world and would blow your head clean off, you've got to ask yourself one question, Do I feel lucky? Well do ya punk?

all fixed :)

SilverShalkin30-May-02 15:39

Re: Is it me, or does there seem to be a bubble of questions with long subjects and nothing of any merit in the actual body of the message.

30-May-02 15:39

did you spell check that?

~SilverShalkin

Rose | [Rose]

Nish Nishant30-May-02 17:57

Nish Nishant

30-May-02 17:57

Tim Smith wrote:
not picking on you redeemer

Frown | :-(

Then, who else are ya picking on?
Moi???

Nish

Regards,
Nish
Native CPian.
Born and brought up on CP.
With the CP blood in him.

device context of picture box control

Speedy30-May-02 13:10

Speedy

30-May-02 13:10

i have a picture box controls on a dialog box.i want to show bitmap on it, on the click event of another dialog. doing so causes DEBUG ASSERTION FAILED! msg first and then image iz displayed on the top left corner of screen instead of picture box. i m trying to solve the problem for the last two weeks but didnt find any solution. Frown | :(

(if i use the device context of Dialog instead of picture box then it works well but when i try to get the device context of picture box it don't.)
if u know something about this problem or have some helping code plz give it to me. thanx

God Helps those who help others. Roll eyes | :rolleyes:

How do i catch when the user selects an item in a listview control with the RIGHT mouse button?

redeemer30-May-02 13:03

redeemer

30-May-02 13:03

Can't quite figure that out yet...

THanks

Re: How do i catch when the user selects an item in a listview control with the RIGHT mouse button?

Tomasz Sowinski30-May-02 13:05

Tomasz Sowinski

30-May-02 13:05

NM_RCLICK doesn't work?

Tomasz Sowinski -- http://www.shooltz.com

- It's for protection
- Protection from what? Zee Germans?

Re: How do i catch when the user selects an item in a listview control with the RIGHT mouse button?

redeemer30-May-02 13:28

redeemer

30-May-02 13:28

Yes, and then create a

NMLISTVIEW *pNmlv;

and assign the value of lParam to it

pNmlv = (NMLISTVIEW *)lParam;

and

if (pNmlv->iItem == -1)

then no item is selected, otherwise some item is selected and the index number of the item is in pNmlv->iItem

Thankuoi Smile | :)

Overiding mouse events

30-May-02 11:51

Hey guys, im trying to figure out how I would override a mouse even in Outlook with an add-in i've made. More specifically, I want have my own dialog pop up when i double click an appointment spot in the calendar. Any help would be nice. Thanks

Variable issues

Stew30-May-02 11:37

Stew

30-May-02 11:37

I apologize for asking this question over and over, but I'm still having trouble with the variables in my application. The problem I am having, for example, is when a CString variable is populated within a particular function, all of the CString variables in that function are populated with the same data and, inexplicably, share the same memory address. Therefore, when the data in one of the variables is changed, all of the others change along with it. I'm not sure what I'm doing wrong. some people have mentioned that I might be overwriting the stack. I'm not sure how to overwrite the stack and so I'm not sure if I'm doing it or how to fix it. Any help would be greatly appreciated.

Bill Wilson30-May-02 11:43

Bill Wilson

30-May-02 11:43

Post some code. It sounds like coding error.

Stew30-May-02 12:01

Stew

30-May-02 12:01

for(int i = 0; i < TempPlaybookFileComboBox.GetCount(); i++)
{
fstream PlaybookFileStream;
CString StrippedFileName;
CString PlaybookFile;
char *pdest;
int result;
int ch = '.';
int slash = '\\';

TempPlaybookFileComboBox.GetLBText(i, PlaybookFileName);

StrippedFileName = PlaybookFileName.Left(PlaybookFileName.GetLength() - 4);

// populate the treectrl
HTREEITEM hti = m_wndPlaybookTree.InsertItem(StrippedFileName);

PlaybookFileStream.open(PlaybookFileLocation + "\\" + PlaybookFileName, ios::binary | ios::in);

while(!PlaybookFileStream.eof())
{
CString PlaybookFilePath;
int PathLength;

PlaybookFilePath = "";

PlaybookFileStream.getline(PlaybookFile.GetBuffer(0), 128, '\n');
PlaybookFilePath = PlaybookFile;
PathLength = PlaybookFile.GetLength();

// strip out the filename from the path-filename combination
pdest = strrchr(PlaybookFile.GetBuffer(0), slash) + 1;
result = pdest - PlaybookFile.GetBuffer(0) + 1;
if (result > 0)
sprintf(PlaybookFile.GetBuffer(0), pdest);

// strip off the extension
pdest = strchr( PlaybookFile.GetBuffer(0), ch );
result = pdest - PlaybookFile.GetBuffer(0) + 1;

// null terminate the string and add to the tree
PlaybookFile.GetBuffer(0)[result - 1] = '\0';
m_wndPlaybookTree.InsertItem(PlaybookFile.GetBuffer(0), hti);

// Allocate memory for new offensive position
ptrPlaybookFileItem = new PlaybookFileRec;
if (ptrPlaybookFileItem == (PlaybookFilePtr)NULL)
{
AfxMessageBox("Unable to allocate memory for Playbook File information", MB_OK);
AfxAbort();
}

ptrPlaybookFileItem->PlaybookFileName = PlaybookFile;
ptrPlaybookFileItem->PlaybookFilePath = PlaybookFilePath;

// Add the Offensive Postion information to the vector
m_PlaybookFiles.push_back(ptrPlaybookFileItem);
}
PlaybookFileStream.close();
}

There's a little snippet of code. The PlaybookFile and PlaybookFilePath variables are mapped to the same memory address.

Bill Wilson30-May-02 12:18

Bill Wilson

30-May-02 12:18

This doesn't look right to me.

PlaybookFileStream.getline(PlaybookFile.GetBuffer(0), 128, '\n');

the argument in GetBuffer causes CString to allocate at least that many characters to the buffer. If your CString object starts out with an empty string and you do a GetBuffer(0) you still have no memory allocated. Try this instead.

PlaybookFileStream.getline(PlaybookFile.GetBuffer(0128), 128, '\n');

You must allso call ReleaseBuffer after modifying the string.