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From:	tonytg13 AT yahoo DOT com (Tony Ganchev)
Newsgroups:	comp.os.msdos.djgpp
Subject:	"delete" crash
Date:	1 Jun 2004 05:43:26 -0700
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Lines:	573
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

Guys, I have the following problem:
I have written a class, implementing dynamic linked list with
elements, containing strings. Unfortunately when I use the Remove
method of the GStringList class, my program crashes. I use DJGPP under
WinXP. I suppose the problem is some sort of segmentation although
there is nothing like SIGSEGV signal, the program just stops
execution. I have made sure that all of the elements are created using
"new". If anyone is eager to help me, here is the source

....................__TYPES.H..............................

#ifndef __TYPES_H_

#define __TYPES_H_



// A byte
typedef unsigned char  BYTE;
// A word - 2 bytes
typedef unsigned short WORD;
// A double word - 4 bytes
typedef unsigned long  DWORD;



#endif

....................__STRING.H.............................

#ifndef __STRING_H_

#define __STRING_H_



#include <string.h>



#include "__types.h"



//****************************************************************************
// GString: a string, representing a line of text in the editor. Has
many
// tools, useful for a text editor
//****************************************************************************
class GString
{
	// Properties ********************************************************
	char *pString; // Pointer to string in memory
public:
	// Construction/Destruction
******************************************
	// Constructor
	GString() { pString = NULL; }
	// Destructor
	~GString() { Empty(); }
	// Methods ***********************************************************
	// Return the string held at the moment
	char *Get() const { return pString; }
	// Return the length of the string
	WORD LengthGet() const { return strlen(pString); }
	// Empties the string
	void Empty();
	// Copies string
	GString &operator=(const GString strFrom);
	GString &operator=(const char *pFrom);
	// Add another string at the end
	void StringAdd(const GString &str);
	void StringAdd(const char *pStr);
	// Concatenate the string with another one
	friend GString operator+(const GString &str1, const GString &str2); 
	friend GString operator+(const GString &str, const char *pStr);
	friend GString operator+(const char *pStr, const GString &str);
	// Return selected character
	char &operator[](const WORD nPos);
	// Add character at the end of the string
	void Add(const char c);
	// Add character in the middle of the string
	void Insert(const char c, const WORD nPos);
	// Remove character from the string
	void Remove(const WORD nPos);
};
//****************************************************************************



//****************************************************************************
// Implementation of GString
//****************************************************************************



//----------------------------------------------------------------------------
// Empties the string
//----------------------------------------------------------------------------
void GString::Empty()
{
	if (pString != NULL) 
		delete [] pString;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Copies string
//----------------------------------------------------------------------------
// pFrom: the string to copy from
//----------------------------------------------------------------------------
// return: Copy of the new string for further assigning
//----------------------------------------------------------------------------
GString &GString::operator=(const char *pFrom)
{
	Empty();
	pString = new char[strlen(pFrom) + 1];
	strcpy(pString, pFrom);
	return *this;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Copies string
//----------------------------------------------------------------------------
// strFrom: the string to copy from
//----------------------------------------------------------------------------
// return: Copy of the new string for further assigning
//----------------------------------------------------------------------------
GString &GString::operator=(const GString strFrom)
{
	return operator=(strFrom.Get());
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Add another string at the end
//----------------------------------------------------------------------------
// pStr: the string to copy from
//----------------------------------------------------------------------------
void GString::StringAdd(const char *pStr)
{
	char *pTemp = new char[LengthGet() + strlen(pStr) + 1];
	strcpy(pTemp, pString);
	strcat(pTemp, pStr);
	Empty();
	pString = pTemp;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Add another string at the end
//----------------------------------------------------------------------------
// str: the string to copy from
//----------------------------------------------------------------------------
void GString::StringAdd(const GString &str)
{
	StringAdd(str.Get());
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Concatenates the string with another one
//----------------------------------------------------------------------------
// str1:
// str2: the string to copy
//----------------------------------------------------------------------------
// return: Copy of the new string for further assigning
//----------------------------------------------------------------------------
GString operator+(const GString &str1, const GString &str2)
{
	GString strTemp;

	strTemp = str1;
	strTemp.StringAdd(str2);
	return strTemp;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Concatenates the string with another one
//----------------------------------------------------------------------------
// str :
// pStr: the string to copy
//----------------------------------------------------------------------------
// return: Copy of the new string for further assigning
//----------------------------------------------------------------------------
GString operator+(const GString &str, const char *pStr)
{
	GString strTemp;

	strTemp = str;
	strTemp.StringAdd(pStr);
	return strTemp;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Concatenates the string with another one
//----------------------------------------------------------------------------
// pStr:
// str : the string to copy
//----------------------------------------------------------------------------
// return: Copy of the new string for further assigning
//----------------------------------------------------------------------------
GString operator+(const char *pStr, const GString &str)
{
	GString strTemp;

	strTemp = pStr;
	strTemp.StringAdd(str);
	return strTemp;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Return selected character
//----------------------------------------------------------------------------
// nPos: position of the selected character
//----------------------------------------------------------------------------
char &GString::operator[](const WORD nPos)
{
	return pString[nPos];
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Add character at the end of the string
//----------------------------------------------------------------------------
// c: character to add
//----------------------------------------------------------------------------
void GString::Add(const char c)
{
	char *pTemp = new char[LengthGet() + 2];
	strcpy(pTemp, pString);
	pTemp[LengthGet()] = c;
	pTemp[LengthGet() + 1] = 0;
	Empty();
	pString = pTemp;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Add character in the middle of the string
//----------------------------------------------------------------------------
// c   : character to add
// nPos: position at which to place
//----------------------------------------------------------------------------
void GString::Insert(const char c, const WORD nPos)
{
	char *pTemp = new char [LengthGet() + 2];
	if (nPos > 0)
		strncpy(pTemp, pString, nPos);
	pTemp[nPos] = c;
	pTemp[nPos + 1] = 0;
	strcat(pTemp, (char *)(pString + nPos));
	Empty();
	pString = pTemp;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Remove character from the string
//----------------------------------------------------------------------------
// nPos: the position to remove the character from
//----------------------------------------------------------------------------
void GString::Remove(const WORD nPos)
{
	char *pTemp = new char [LengthGet()];
	if (nPos > 0)
		strncpy(pTemp, pString, nPos);
	pTemp[nPos] = 0;
	strcat(pTemp, (char *)(pString + nPos + 1));
	Empty();
	pString = pTemp;
}
//----------------------------------------------------------------------------



#endif

....................__SLIST.H.............................

#ifndef __SLIST_H_

#define __SLIST_H_



#include <malloc.h>



#include "__types.h"
#include "__string.h"



//****************************************************************************
// GStringNode: Element of the GStringList dynamic linked list
//****************************************************************************
class GStringNode
{
public:
	GString      strLine;
	GStringNode *pNext;
};
//****************************************************************************



//****************************************************************************
// GStringList: A simple dynamic linked list to contain lines of text
//****************************************************************************
class GStringList
{
	// Properties ********************************************************
	GStringNode *pHead;  // Pointer to first element in list
	DWORD        nCount; // Number of elements in list
public:
	// Construction/Destruction
******************************************
	// Constructor
	GStringList();
	// Destructor
	~GStringList();
	// Methods ***********************************************************
	// Return pointer to selected node
	GStringNode *Get(const DWORD nPos);
	// Return the number of elements
	DWORD CountGet() const { return nCount; }
	// Return selected string
	GString &operator[](const DWORD nPos);
	// Add element at the end of the list
	void Add(const GString &str);
	// Insert element in the middle of the list
	void Insert(const GString &str, const DWORD nPos);
	// Remove an element
	void Remove(const DWORD nPos);
	// Remove all elements
	void Clear();
};
//****************************************************************************



//****************************************************************************
// Implementation of GStringList
//****************************************************************************



//----------------------------------------------------------------------------
// Constructor
//----------------------------------------------------------------------------
GStringList::GStringList()
{
	pHead = NULL;
	nCount = 0;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Destructor
//----------------------------------------------------------------------------
GStringList::~GStringList()
{
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Return pointer to selected node
//----------------------------------------------------------------------------
// nPos: position of the node
//----------------------------------------------------------------------------
GStringNode *GStringList::Get(const DWORD nPos)
{
	printf("Requested %lu\n", nPos);
	DWORD        n;
	GStringNode *pTemp = pHead;
	if (nPos < nCount)
	{
		for (n = 1; n <= nPos; n++)
			pTemp = pTemp->pNext;

		return pTemp;
	}
	return NULL;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Return selected string
//----------------------------------------------------------------------------
// nPos: position of the node
//----------------------------------------------------------------------------
GString &GStringList::operator[](const DWORD nPos)
{
	return Get(nPos)->strLine;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Add element at the end of the list
//----------------------------------------------------------------------------
// str: string of the element
//----------------------------------------------------------------------------
void GStringList::Add(const GString &str)
{
	GStringNode *pTemp = new GStringNode;
	pTemp->strLine = str;
	pTemp->pNext = NULL;

	if (nCount == 0)
		pHead = pTemp;
	else
		Get(nCount - 1)->pNext = pTemp;

	nCount++;
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Insert element in the middle of the list
//----------------------------------------------------------------------------
// str : string of the element
// nPos: position of the node
//----------------------------------------------------------------------------
void GStringList::Insert(const GString &str, const DWORD nPos)
{
	GStringNode *pTemp = new GStringNode;

	pTemp->strLine = str;

	if (nPos < nCount)
	{
		if (nPos == 0)
		{
			pTemp->pNext = pHead;
			pHead = pTemp;
		}
		else
		{
			pTemp->pNext = Get(nPos);
			Get(nPos - 1)->pNext = pTemp;
		}

		nCount++;
	}
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Remove an element
//----------------------------------------------------------------------------
// nPos: position of the node
//----------------------------------------------------------------------------
void GStringList::Remove(const DWORD nPos)
{
	GStringNode *pTemp;

	if (nPos < nCount && nCount > 0)
	{
		if (nCount == 1)
			delete pHead;
		else if (nPos == 0)
		{
			printf("------\n");
			pTemp = pHead;
			printf("......\n");
			pHead = pHead->pNext;
			printf(";;;;;;\n");
			delete pTemp;
			printf("//////\n");
		}
		else if (nPos == nCount - 1)
			delete Get(nPos);
		else
		{
			pTemp = Get(nPos + 1);
			delete Get(nPos);
			Get(nPos - 1)->pNext = pTemp;
		}

		nCount--;
	}
}
//----------------------------------------------------------------------------



//----------------------------------------------------------------------------
// Remove all elements
//----------------------------------------------------------------------------
void GStringList::Clear()
{
}
//----------------------------------------------------------------------------



#endif

....................DOSED.CPP.............................

#include <conio.h>
#include <stdio.h>
#include "__string.h"
#include "__slist.h"



int main()
{
        GStringList l;
        GString     s;
        
        clrscr();

        s = "Line1";
        l.Add(s);
        s = "Line2";
        l.Insert(s, 0);
        s = "Line3";
        l.Insert(s, 1);
	s = "Line4";
	l.Insert(s, 2);
	s = "Line5";
	l.Insert(s, 3);
	l.Remove(0);

        printf("0: %s\n", l[0].Get());
        printf("1: %s\n", l[1].Get());
        printf("2: %s\n", l[2].Get());
	printf("3: %s\n", l[3].Get());

        return 0;
}

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