How to avoid this exception?

[Gokulnathvc]

I am using char** variable to download a file from http and save it in local disk. I have used char* variable and used calloc() and malloc() to allocate memory and free it after its usage.Also used a file for logging concept. I have used pixmap to set background for the dialog. Everything works fine. But after sometime. i get this error.. control automatically goes to this system QT file. and gives segmentation fault error.How to fix this?

QClipData::~QClipData()
{
	if(m_clipLines)
	   free(m_clipLines);
	if(m_spans)
	   free(m_spans);
}

QClipData::~QClipData()
{
	if(m_clipLines)
	   free(m_clipLines);
	if(m_spans)
	   free(m_spans);
}

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Sometimes, it shows this error and control goes here: Why it is happening?

QImageData::~QImageData()
{
	if(is_cached)
	QImagePixmapCleanupHooks::executeImageHooks((((qint64) ser_no)<<32) | ((qint64)	detach_no):
	delete paintEngine:
	if(data && own_data)
		free(data);

QImageData::~QImageData()
{
	if(is_cached)
	QImagePixmapCleanupHooks::executeImageHooks((((qint64) ser_no)<<32) | ((qint64)	detach_no):
	delete paintEngine:
	if(data && own_data)
		free(data);

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And sometimes, it gives the exception and the control goes here.

Dump of assembler code for function ntdll!RtlEqualPrefixSid:
0x77543aac  <+0>:            	mov    $0x890c568b,%eax
0x77543ab1  <+5>:            	push   %ebp
0x77543ab2  <+6>:            	cwtl
0x77543ab3  <+7>:            	mov    (%edx),%edx
0x77543ab5  <+9>:            	mov    0x4(%edi),%edi
        End of assembler dump.

Dump of assembler code for function ntdll!RtlEqualPrefixSid:
0x77543aac  <+0>:            	mov    $0x890c568b,%eax
0x77543ab1  <+5>:            	push   %ebp
0x77543ab2  <+6>:            	cwtl
0x77543ab3  <+7>:            	mov    (%edx),%edx
0x77543ab5  <+9>:            	mov    0x4(%edi),%edi
        End of assembler dump.

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[ChrisW67]

This question has nothing to do with Qt.

You are using a null or invalid pointer in your code. Run the program in a debugger to find out.

[T_h_e_o]

What I think is strange is that you use C and C++ (de)allocations intermixed (new/delete and malloc/free). Since you are programming in C++, there is no need to use malloc/free, better use new/delete. By using both, you have the risk of using the wrong deallocation compared to the allocation, which may lead to anything, including crashes.

[high_flyer]

Are the pointers your trying to delete really initialized?
Don't mix new with free and alloc with delete.
Since you are in a C++ environment, use only new and delete.