Using 'delete' and its effect on local and variables being passed

[rasmidas]

I have a function

void AddItem(char* buffer, char* items[], int& index)
{
   char* temp = new char[strlen(buffer) + 1];
 
   strcpy(temp, buffer);
 
   items[index] = temp;
 
   index++;
}
 

Here we are allocating memory space for temp using new.
But we are not deleting it.
The varible temp is not used anywhere outside the function.
But buffer and index are being used.
Should I use delete here for temp or not?
Please let me know.
Thanks in advance.

[Banfa]

Here we are allocating memory space for temp using new.
But we are not deleting it.
The varible temp is not used anywhere outside the function.
But buffer and index are being used.
Should I use delete here for temp or not?

The pointer to the buffer stored in temp is copied to Items, therefore the pointer is not lost, not deleting it here is not intrinsically a problem (it may of course be a problem in the context of the rest of the program).

[ravenspoint]

The variable temp is an automatic, which means it is automatically deleted when the routine exits.

If you are asking about freeing the memory allocated in the routine ( and pointed to by temp ) you cannot do that until you are finished using the memory. It will not be freed automatically, so you have to look after that chore somewhere - or exit the program.

[weaknessforcats]

If you are asking about freeing the memory allocated in the routine ( and pointed to by temp ) you cannot do that until you are finished using the memory. It will not be freed automatically, so you have to look after that chore somewhere - or exit the program.

To rasmidas:

You cannot tell from a pointer whether it is safe to delete it. The only time it is safe is when there are no other copies of it anywhere else in the program. You might read the article on Handle Classes in the C/C++ Articles forum. These are the smart pointers that are often used to control safe ddeleting of pointers.

[sicarie]

Just FYI - I changed the title of the thread to better describe the issue.

[rasmidas]

This temp is a local pointer variable and is not being used anywhere else in the program. However buffer, index and items are being used in the program. If I will use
delete temp;
at the end of this function, that is if I will write as below:
void AddItem(char* buffer, char* items[], int& index)
{
char* temp = new char[strlen(buffer) + 1];

strcpy(temp, buffer);

items[index] = temp;

index++;

delete temp;
}

will it affect the program or it will be correct after adding delete statement.
Thanks in advance.

[gpraghuram]

This temp is a local pointer variable and is not being used anywhere else in the program. However buffer, index and items are being used in the program. If I will use
delete temp;
at the end of this function, that is if I will write as below:
void AddItem(char* buffer, char* items[], int& index)
{
char* temp = new char[strlen(buffer) + 1];

strcpy(temp, buffer);

items[index] = temp;

index++;

delete temp;
}

will it affect the program or it will be correct after adding delete statement.
Thanks in advance.

Hi
If you delete the temp then the item will be referring to an invalid memoy location.
You should delete this memory when you dont need item like delete item[i];

Raghuram

[rasmidas]

Thanks all. Now I am clear. Thanks a lot.

[rasmidas]

Here I am pasting the function where I am calling the above AddItem() function.

int PopulateClearing ( sDOC_SOURCE* DocSource, char* items[], int& index )
{
   char buffer[128] = "";
   char msg[199] = "";
 
   RWCString swiftFlag = "N";
   RWCString clearingSys = "";
   RWCString newSwift = "Y";
 
   int swiftCount = 1;
 
   if ( DocSource->Function == sDF_INCEPTION )
   {
      // sprintf ( msg, "Entered PopulateClearing() for trade '%s'",
      //                DocSource->Trade.Base.TradeID.Num );
      // mLogMessage ( msg );
 
      try
      {
         if ( IsSwiftable ( &(DocSource->Trade) ) == sTRUE )
         {
              swiftFlag = "Y";
 
              if ( IsSwapClearable ( &DocSource->Trade ) == sTRUE )
              {
                 clearingSys = "SWAPCLEAR";
              }
 
         }
         if ( ( swiftFlag == "Y" ) ||
              ( sTT_FRA == DocSource->Trade.Base.TradeType ) )
         {
            sENTITY* pEntity = sGetEntityByName( "cSWIFTREC" );
            cSWIFTREC* pSwiftRec = NULL;
 
            if ( sEntityCreate( pEntity, (void**)&pSwiftRec ) != sSUCCESS )
            {
               mLogMessage( "Error creating cSWIFTREC entity" );
            }
            else
            {
               strcpy( pSwiftRec->TradeId.Num, DocSource->Trade.Base.TradeID.Num );
               pSwiftRec->TradeType = DocSource->Trade.Base.TradeType;
 
               if ( sEntityDBRead( pEntity, pSwiftRec, "EQUAL", 00 ) == sSUCCESS )
               {
                  newSwift = "N";
                  swiftCount = ++pSwiftRec->SwiftCount;
               }
            }
         }
/
                  newSwift = "N";
                  swiftCount = ++pSwiftRec->SwiftCount;
               }
            }
         }
      }
      catch ( ... )
      {
         mLogMessage ( "Exception in PopulateClearing() caught :" );
         mLogMessage ( "  IsSwiftable reset to 'N' in the BLOB" );
         mLogMessage ( "  ClearingSystem reset to '' in the BLOB" );
         swiftFlag = "N";
         clearingSys = "";
      }
 
 
      // sprintf ( msg, "BLOB field 'IsSwiftable' set to '%s' for trade '%s'",
      //                swiftFlag.data(), DocSource->Trade.Base.TradeID.Num );
      // mLogMessage ( msg );
 
      // sprintf ( msg, "BLOB field 'ClearingSystem' set to '%s' for trade '%s'",
      //                clearingSys.data(), DocSource->Trade.Base.TradeID.Num );
      // mLogMessage ( msg );
 
 
      sprintf ( buffer, "IsSwiftable=\"%s\";\n", swiftFlag.data() );
      AddItem(buffer, items, index);
 
      sprintf ( buffer, "ClearingSystem=\"%s\";\n", clearingSys.data() );
      AddItem(buffer, items, index);
 
      sprintf ( buffer, "NewSwift=\"%s\";\n", newSwift.data() );
      AddItem(buffer, items, index);
 
      sprintf ( buffer, "SwiftCount=\"%d\";\n", swiftCount );
      AddItem(buffer, items, index);
 
   }
 
 
   return sSUCCESS;
}
 

Please let me know how and where to delete the memory allocated to temp.
Thanks in advance.

[gpraghuram]

Here I am pasting the function where I am calling the above AddItem() function.

int PopulateClearing ( sDOC_SOURCE* DocSource, char* items[], int& index )
{
   char buffer[128] = "";
   char msg[199] = "";
 
   RWCString swiftFlag = "N";
   RWCString clearingSys = "";
   RWCString newSwift = "Y";
 
   int swiftCount = 1;
 
   if ( DocSource->Function == sDF_INCEPTION )
   {
      // sprintf ( msg, "Entered PopulateClearing() for trade '%s'",
      //                DocSource->Trade.Base.TradeID.Num );
      // mLogMessage ( msg );
 
      try
      {
         if ( IsSwiftable ( &(DocSource->Trade) ) == sTRUE )
         {
              swiftFlag = "Y";
 
              if ( IsSwapClearable ( &DocSource->Trade ) == sTRUE )
              {
                 clearingSys = "SWAPCLEAR";
              }
 
         }
         if ( ( swiftFlag == "Y" ) ||
              ( sTT_FRA == DocSource->Trade.Base.TradeType ) )
         {
            sENTITY* pEntity = sGetEntityByName( "cSWIFTREC" );
            cSWIFTREC* pSwiftRec = NULL;
 
            if ( sEntityCreate( pEntity, (void**)&pSwiftRec ) != sSUCCESS )
            {
               mLogMessage( "Error creating cSWIFTREC entity" );
            }
            else
            {
               strcpy( pSwiftRec->TradeId.Num, DocSource->Trade.Base.TradeID.Num );
               pSwiftRec->TradeType = DocSource->Trade.Base.TradeType;
 
               if ( sEntityDBRead( pEntity, pSwiftRec, "EQUAL", 00 ) == sSUCCESS )
               {
                  newSwift = "N";
                  swiftCount = ++pSwiftRec->SwiftCount;
               }
            }
         }
/
                  newSwift = "N";
                  swiftCount = ++pSwiftRec->SwiftCount;
               }
            }
         }
      }
      catch ( ... )
      {
         mLogMessage ( "Exception in PopulateClearing() caught :" );
         mLogMessage ( "  IsSwiftable reset to 'N' in the BLOB" );
         mLogMessage ( "  ClearingSystem reset to '' in the BLOB" );
         swiftFlag = "N";
         clearingSys = "";
      }
 
 
      // sprintf ( msg, "BLOB field 'IsSwiftable' set to '%s' for trade '%s'",
      //                swiftFlag.data(), DocSource->Trade.Base.TradeID.Num );
      // mLogMessage ( msg );
 
      // sprintf ( msg, "BLOB field 'ClearingSystem' set to '%s' for trade '%s'",
      //                clearingSys.data(), DocSource->Trade.Base.TradeID.Num );
      // mLogMessage ( msg );
 
 
      sprintf ( buffer, "IsSwiftable=\"%s\";\n", swiftFlag.data() );
      AddItem(buffer, items, index);
 
      sprintf ( buffer, "ClearingSystem=\"%s\";\n", clearingSys.data() );
      AddItem(buffer, items, index);
 
      sprintf ( buffer, "NewSwift=\"%s\";\n", newSwift.data() );
      AddItem(buffer, items, index);
 
      sprintf ( buffer, "SwiftCount=\"%d\";\n", swiftCount );
      AddItem(buffer, items, index);
 
   }
 
 
   return sSUCCESS;
}
 

Please let me know how and where to delete the memory allocated to temp.
Thanks in advance.

HI,
Since the logic is yours you shuld in a better position to tell where to put the delete function.

Raghuram

[weaknessforcats]

Please let me know how and where to delete the memory allocated to temp.

It's never safe to delete temp. That's because the address of temp has been copied into another array.

It you could only know that the temp you want to delete does not exist anywhere else in the program, then you could delete it.

You need a smart pointer.

Read the article on Handle classes the C/C++ Articles forum. In that article is a template for a smart pointer that you can copy into your own code and start using.

As a rule, the single most dangerous thing you can do in a C++ program is to pass pointers around. When you do, you have to ensure that the objects pointed at are still there.