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Please help with my own String Class - weird assertions !!


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#1 Phillip Schuster   Members   -  Reputation: 122

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Posted 07 November 1999 - 09:38 AM

Hi all !!

I really have a problem here. I need to write my own String Class (for Visual C++ 6.0) because I didn't find one ;((

Now, when I want to use the "Insert" member function I get assertion failures. According to MSDN these are produced from the debug-version of free and malloc.

Here is the source:

// String.cpp: Implementierung der Klasse CString.
//
//////////////////////////////////////////////////////////////////////

#include "stdafx.h"
#include "String.h"
#include
#include "3dengine.h"

#ifdef _DEBUG
#undef THIS_FILE
static char THIS_FILE[]=__FILE__;
#endif

#define UpdateBuffer(x) free(buffer);buffer=(char*)malloc(x+1);length=x;
#define Clear(name) memset(name,0,strlen(name));
#define CreateBuffer(name,x) char* name; name=(char*)malloc(x+1);Clear(name);
#define CreateMem(x) (char*)malloc(x+1);
#define SaveFree(name) if (name != NULL) {free(name);} name = NULL;

//////////////////////////////////////////////////////////////////////
// Konstruktion/Destruktion
//////////////////////////////////////////////////////////////////////

CString::CString()
{
//Allocate a default buffer
buffer = CreateMem(40);
length = 40;
}

CString::CString(char* string)
{
int len = strlen(string);

buffer = CreateMem(len);
length = len;

strcpy(buffer,string);
}

CString::~CString()
{
SaveFree(buffer);
}

void CString::Insert(char *string, int pos)
{
int len = strlen(string);
int curlen = strlen(buffer);

if (pos != -1) {
char left[255];
char right[255];

strncpy(left,buffer,pos);
memset(&left[pos],0,1);
strncpy(right,&buffer[pos],curlen-pos);
memset(&right[curlen-pos],0,1);

//If we need more memory, kill the old buffer and allocate a new one
if ((len + curlen) > length) {
CreateBuffer(temp,curlen);
strcpy(temp,buffer);
UpdateBuffer(len+curlen);
strcpy(buffer,temp);
SaveFree(temp);
}

sprintf(buffer,"%s%s%s",left,string,right);

} else {
//If we need more memory, kill the old buffer and allocate a new one
if ((len + curlen) > length) {
CreateBuffer(temp,curlen);
strcpy(temp,buffer);
UpdateBuffer(len+curlen);
strcpy(buffer,temp);
SaveFree(temp);
}

strcat(buffer,string);
}

}


The error I get is something like that:

Debug Error!
Program
DAMAGE: after Normal block (#NNN) at 0xNNNNNNNN

It seems that the memory allocated before gets corrupted in some way, but why and where ??

Phillip Schuster




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#2 felisandria   Members   -  Reputation: 739

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Posted 04 November 1999 - 02:08 PM

Well, I haven't seen that particular error before... but you should probably check in the stdafx.h and make sure there weren't any MFC-type includes, as CString is the name of the string class for MFC.

Why don't you just use CString from MFC (it's not part of the CObject hierarchy, MFC haters stop screaming about code bloat on this one... *smile*) or if you refuse to use MFC, use the basic_string from STL?

-fel


#3 Xai   Crossbones+   -  Reputation: 1328

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Posted 06 November 1999 - 03:19 AM

I haven't read all of your code yet, cause I wanted to get my first opinions out first. I'll try to dig through the code after I get some sleep (been up 33 hours and counting).

1) felisandria might be right. ALWAYS watch out about using CBlahBlah for a class name. This is NOT the standard way to name a class, it is MICROSOFT'S class namespace. Way back, all of the big compiler/library vendors got together and each agreed to preface their classes and such with a certain letter (some got 2 letters I believe). Microcoft took C, like CString (which IS in MFC AND is what you are trying to use) and CPoint, and Borland got T, so there stuff is named TControl, TString, etc.... So it's always nice to avoid these ESPECIALLY the C ones when you are using AFX files and microsoft includes and compilers (cause you might overlap their names). The AFX header files are NOT needed. You can get a project without them by choosing EMPTY projcet (instead of a "sample app") when you make a new project. This avoid any stray MFC issues. Then just add your files to the project like normal, and build.


#4 Splat   Members   -  Reputation: 122

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Posted 06 November 1999 - 10:14 AM

If you don't want to rename your class, you could also wrap it in a new namespace, like:

namespace My {
class CString {
...
};
}

then access it like My::CString. That will keep it from conflicting with the (damn) MFC CString.

- Splat


#5 Phillip Schuster   Members   -  Reputation: 122

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Posted 07 November 1999 - 09:38 AM

Hi all !!

Thanks for all your help. I know I might run into trouble with my C... Classes, but I am so damn used to them. I really tried to use others, but CCLASSNAME is what I like and use ) Ok, I have found out what it was. It seems that somehow the free and malloc stuff got confused if allocating memory and then copying strings around.

I now use calloc instead of malloc and everything works fine )

Phillip





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