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You can't do that and teh reason why is that in your second implementation you are trying to set the value of the pointer and not of the character array. And you need to actaully copy the memory containg the "AAA" string to the memory that the pointer points to.
Hope this helps
Peter
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in the second, you are assigning the address of a local variable (val is local to the function) to a non-local variable. a local address is meaningless when used outside the function.
-c
To explain Donald Knuth's relevance to computing is like explaining Paul's relevance to the Catholic Church. He isn't God, he isn't the Son of God, but he was sent by God to explain God to the masses.
/. #3848917
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Many thanks! I think I get it.
So if I had
func(int & abc)
{
int a=9;
abc=a;
}
then when called like
int zz;
func(zz);
zz will be equal to 9.
Is this correct? And we didnt have to copy anything because we're not dealing with addresses, but values.
Thanks again,
ns
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Yep, that's correct.
In your previous strcpy() question, you must ensure that the target string has enough storage allocated. For example, this will fail:
char strMyString [8];
myFunc (strMyString);
...
void myFunc (char* pString)
{
strcpy (pString, "Hello, world!");
}
/ravi
Let's put "civil" back into "civilization"
http://www.ravib.com
ravib@ravib.com
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Function scope would be a good place to start.
You wrote the following function...
ns wrote:
MyFunc(char* abc)
{
char* val = "aaa";
abc = val;
}
It has to do with both pointers and with memory allocation.
First by reassigning pointers such as:
ns wrote:
abc = val
you are now pointing the incoming character pointer to the same memory as 'val'. Remember though, there are two things going on here.
First: Function scope does not allow the changes to abc to be reflected to the caller. The actual value that is passed in as 'abc' is not stored at the same location as the orginal 'abc'. The following code trys to demonstrate the timing and values of the pointers.
Main
{
char* abc = "Home";
// abc = memory addr = 0x00000a, *abc (contents of abc or memory 0x0000a is "H")
MyFunc(abc);
// FUNCTION EMBEDDED TO DEMOSTRATE TIMING
MyFunc(char* abc)
{
char* val = "aaa";
// val = memory addr = 0x01000, *val (contents of val) is "a"
// abc = memory addr = 0x0000a, *val (contes of abc) is "H"
abc = val;
// val = memory addr = 0x01000, *val (contents of val) is "a"
// abc = memory addr = 0x01000, *val (contes of abc) is "a"
}
// abc is reset by the stack back to the original. This is function scope.
// abc = memory addr = 0x00000a, *abc (contents of abc or memory 0x0000a is "H")
}
Second even if you corrected this to pass a pointer to a pointer:
(pass in a pointer to the pointer where the memory for the string is)
pabc->abc->"The string"
pabc = 0x02000 which is the memory addr of abc
abc = 0x0000a which is the memory where the string resides.
MyFunc(char** pabc)
{
char* val = "aaa";
*pabc = val;
}
It changes to pabc->val->"aaa" and pabc->abc->"aaa" while still in the function call. However remember that the function releases its stack values when it exits so we cannot guarantee that someone else will not write to that memory. So the memory that was at the orginal abc pointer is still allocated, but the memory at val or the new abc is released and can be unexpected garbage.
When you use:
ns wrote:
strcpy(abc,val)
you are physically reassigning memory from one place to another. You are retaining the orginal area in memory for each string and moving the contents. A very simple rewrite of strcpy is this:
strcpy(char* a, char* b)
{
// look for an ending null termination
while (*b != '0')
{
*a++ = *b++;
}
}
Notice it is changing the value of what it is pointing to and not where it is pointing. This allows it to move or copy the string in to memory that exists and across the stack reset from functions. Also notice I can increment the pointers and not affect the values that were passed in because of function scope.
Just to let you know I hate text and wish I could draw some pictures, but I tried my best to illustrate the point in English. Let me know if you need more clarification or maybe someone else can clarify what I said.
Brian
If you start a fire for a man, he will be warm for a day. If you start that same man on fire, he will be warm for the rest of his life.
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Generally, it is better to uses std::string class instead of using raw pointers. Far more easier to uses and less error-prone.
And for the rest, many people have already answer the question.
Philippe Mori
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Even though MS is the most resourceful software comapny in the world and hires the most accadmecally qualified and supposedly the most intelligent developerers, it does not produce innovative ,imaginative or quality software on a consistant basis. Instesd it produces buggy software tested on it's smug users through a a number of versions. Not that MS software isn't good or the company is evil, but with its awesome financial resources, though the company could do better,it doesnt. Why?
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troll-1 wrote:
Why?
Because they didn't hire you? Anyway, VC board isn't a place to ask this kind of question. Go to lounge or soapbox instead.
Tomasz Sowinski -- http://www.shooltz.com
- It's for protection
- Protection from what? Zee Germans?
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Hello,
I'm here to ask what message is sent when the dialog bar is moved to a position where it can be docked, because I want to change its appearance and size depending on the side it gonna be docked.
thanks,
Guy.
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Hi,
i want to write two programs, which are able to switch to the other program (if they are running). Both programs have a button. If you press this button:
1. The other program is launching if it is not running.
2. If the other program is running (multiple instance possible), the window of one of these instances should be pop to the front of the desktop.
Has anybody an idea?
Ciao
f.o.b
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The most important thing is to get a handle to teh window in the other application. You can do this with GetWindow. You may have to do some searching through all of the windows, but you will be able to find the window in the other app with this API.
Next you can call SetForegroundWindow on that window handle. This will bring that window to teh foreground and give it keyborad access.
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!
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Do a search for AttachThreadInput in here over the last weeks or so.
There are issues with SetForegroundWindow that must be worked around
for your plan to succeed. (unless you still run Win95  )
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I want to get the keyvalue out:
void DLLGetValue(int imageIndex,CString key,char* keyvalue)
{
if (imageIndex == 0)
{
if (key=="abc") value="aa";
if(key=="def")value = "ss";
if (key == "aaa")value = "dd";
}
strcpy(keyvalue, value);
}
and its called like:
std::set<cstring>::iterator it = pDoc->m_keySet.begin();
for (; it != pDoc->m_keySet.end() 
{
char* p = new char[2]; p[0] = p[1] = '\0';
int size=30;
if (size)
{
delete[] p;
p = new char[size + 1];
DLLGetValue(imageIndex,*it,p);
}
When p comes back, its full of garbage. WHat did I do wrong?
Thanks,
ns
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From the top of my head - you should have at least three character buffer for "aa", "ss" or "dd" - don't forget about trailing null character. However, why on Earth would one mix these manual, low-level, stinky character operations with STL? Can't you just use string& as keyvalue?
Tomasz Sowinski -- http://www.shooltz.com
- It's for protection
- Protection from what? Zee Germans?
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Thanks. You are quite right about CString being a better choice, but I'm simulating a DLL that pre-exists and returns a char *, so I had to venture into the not-so-friendly world of char. Eventaully it replaces my fake function.
Thanks again,
ns
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OOps,I meant it didnt run at all, didnt compile errors were like:
C:\Trainer\Train\Train1\Train1View.cpp(796) : error C2440: '=' : cannot convert from 'char [7]' to 'int'
which didnt clue me in to the fact that I had not declared "value" . I'm sure that error was there too, but I didnt see it buried in all the compiler warnings for STL.
It works now.
Thanks,
ns
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(I know I'm not answering your question, but...) You should bracket your code within <pre> and </pre> tags in order to preserve the indentation so that it's easy to read. The new formatting buttons that Chris introduced makes it easy to do this.
Thanks,
/ravi
Let's put "civil" back into "civilization"
http://www.ravib.com
ravib@ravib.com
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ns wrote:
I'm sure that error was there too, but I didnt see it buried in all the compiler warnings for STL.
You can get rid of those warnings with a pragma.
Christian
come on all you MS suckups, defend your sugar-daddy now. - Chris Losinger - 11/07/2002
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I want to integrate a version for my DLL... How to do that???
Thanks in advances
Hello World!!!
from Raphaël
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Add a resource script (.rc) file to the project, then select the "Resources" tab within VC++ and add a version resource.
/ravi
Let's put "civil" back into "civilization"
http://www.ravib.com
ravib@ravib.com
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I was the beginner of the learner c language now meet some proble instead donot how to apply the colour source in my program so hope can u help me? The project that want to apply in the background text and text that hv the colour.
Thank you.
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I'm sorry, but I can't understand what you're trying to ask 
--
Help me! I'm turning into a grapefruit!
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i want ask how to apply the colour in the c language program while we execute the program that colour will appear at the MS-DOS Prompt
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i need the colour source code and that function how to use i hv try before that with using the #include <graphics.h> to apply the color for my text and text background color but cannot work
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