Mismatch free() / delete / delete [C++]


 
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Operating Systems Linux Mismatch free() / delete / delete [C++]
# 1  
Old 11-03-2016
Code Mismatch free() / delete / delete [C++]

Dear All,

I got the valgrind report as below [c++]

Code:
Mismatch free() / delete / delete []
at 0x4006895: operator delete(void*) (vg_replace_malloc.c:480)
by 0x8EA6D11: corefunction.

I supect that it is expect me to write free() instead of delete p1.
Given the the code.


I have the structure.

Code:
struct Pack
{
    unsigned int A;
    unsigned int B;
    unsigned int c;
    unsigned int D;    
}
 
 
int corefunction()
{
 
 
    Pack *p1=new Pack;
    I filled the value for the p1 object.
    I called a virtual funcion by passing the p1 like this
    Send((void*)p1); //
 
 
    if(p1)
        delete p1;    // Here is the place where i have the doubt that wheher is it expecting to deallocate with free().
 
 
    return 0;
}    
 
bool Send(void* &get_SendData) 
{  
    sendNextLevel(get_SendData  )
}
     
char* sendNextLevel(void* data)
{
                dataLen = sizeof(PackedSysTime);
 
 
                    Pack* txData = NULL;
                    txData = (Pack*)data;
}

since we have converted void pointer to struct without new operator like c-style casting, does it expecting us to write free while we deallocate the memory

Thank you.

Last edited by Corona688; 11-03-2016 at 12:05 PM..
# 2  
Old 11-03-2016
No, this looks okay. I suspect something in the large amounts of code you haven't posted is corrupting the heap and causing delete to fail.

What is a "void * &" ? Why not just "void *" ? Or better yet, "const void *" ?
# 3  
Old 11-03-2016
Quote:
Originally Posted by Corona688
No, this looks okay. I suspect something in the large amounts of code you haven't posted is corrupting the heap and causing delete to fail.

What is a "void * &" ? Why not just "void *" ? Or better yet, "const void *" ?
.It is void * &. It's legacy and huge code . So I have written in simple way to understand. But this the flow .
I feel tha i may need to use static cast to convert void pointer to structure.
Please give me suggestions on what could be the issue for mismatch delete
# 4  
Old 11-03-2016
To repeat: There is nothing wrong in the code you posted. There might be things wrong in the code you didn't post, but how would I ever know? I can only make wild guesses.

Wild guess #1: "void * &" is a really weird type. The only reason I can think of to do that, is if Send() is designed to alter the value of p1 in main itself. Print its integer value, before and after, to cerr or stderr to make sure it's not being changed. Feeding a mangled pointer into delete can cause an error like that.

Wild guess #2: You say "you called a virtual function by passing p1 like this", but Pack is a structure with no member functions, virtual or otherwise: It is completely normal and proper to typecast it to (void *). So where does this virtual thing enter the equation? If your structure is actually something completely different, please tell me now.

Last edited by Corona688; 11-03-2016 at 02:20 PM..
# 5  
Old 11-03-2016
To repeat structure has the data

This is the structure.
Code:
struct Pack
{
    unsigned int A;
    unsigned int B;
    unsigned int c;
    unsigned int D;    
}

You are right that send is to alter the value of Struct p1.

Filled the structure at first before calling Send((void*)p1);

Virtual function has the structure as an argument.


My query ia that who am I getting the
Code:
Mismatch free() / delete / delete []
at 0x4006895: operator delete(void*) (vg_replace_malloc.c:480)
by 0x8EA6D11: corefunction.


Moderator's Comments:
Mod Comment Please use CODE tags as required by forum rules!

Last edited by RudiC; 11-03-2016 at 03:28 PM.. Reason: Added CODE tags.
# 6  
Old 11-03-2016
Quote:
Originally Posted by SA_Palani
You are right that send is to alter the value of Struct p1.
Changing its contents won't cause a crash.

You actually can't typecast things in the way you show in your example, which leaves me more and more curious to what you're actually doing.

That it's passed as a * & gives it the ability to reach in and mangle p1 itself - the pointer.

What I mean is this:

Code:
#include <iostream>
using namespace std;

void mangle_pointer(char * & x) {
        // Set the pointer to a blatantly wrong value
        x = (char *)123456789;
}

int main(void) {
        char *mem=new char;

        cerr << "mem is " << (unsigned long)mem << endl;

        mangle_pointer(mem);

        cerr << "mem is now "<< (unsigned long)mem <<
          " and will crash when deleted" << endl;

        delete mem; // Deleting any value that you didn't get from new is bad
}

This is a trivial example. Tracking down memory crashes is usually a lot harder, the crash is generally a side-effect of an overrun which stomped on the values of your variables or some important hidden values inside the heap itself. An overrun can leap straight through rational boundaries and stomp on whatever happens to be next to it in memory, with no regard for the line order of your program. If the overrun happened to something in a local variable, this can corrupt other local variables, or corrupt your return vector and cause a crash next time you return from any function. If it happened in the heap, it can corrupt other things you have stored in the heap, or corrupt the heap itself, causing delete to mess up in strange ways the next time you delete anything.

This is to say, "delete myvariable" crashing often has nothing to do with "myvariable". Debris can land far away from an explosion.

Last edited by Corona688; 11-03-2016 at 07:12 PM..
# 7  
Old 11-04-2016
Quote:
Originally Posted by Corona688
Changing its contents won't cause a crash.

You actually can't typecast things in the way you show in your example, which leaves me more and more curious to what you're actually doing.

That it's passed as a * & gives it the ability to reach in and mangle p1 itself - the pointer.

What I mean is this:

Code:
#include <iostream>
using namespace std;

void mangle_pointer(char * & x) {
        // Set the pointer to a blatantly wrong value
        x = (char *)123456789;
}

int main(void) {
        char *mem=new char;

        cerr << "mem is " << (unsigned long)mem << endl;

        mangle_pointer(mem);

        cerr << "mem is now "<< (unsigned long)mem <<
          " and will crash when deleted" << endl;

        delete mem; // Deleting any value that you didn't get from new is bad
}

This is a trivial example. Tracking down memory crashes is usually a lot harder, the crash is generally a side-effect of an overrun which stomped on the values of your variables or some important hidden values inside the heap itself. An overrun can leap straight through rational boundaries and stomp on whatever happens to be next to it in memory, with no regard for the line order of your program. If the overrun happened to something in a local variable, this can corrupt other local variables, or corrupt your return vector and cause a crash next time you return from any function. If it happened in the heap, it can corrupt other things you have stored in the heap, or corrupt the heap itself, causing delete to mess up in strange ways the next time you delete anything.

This is to say, "delete myvariable" crashing often has nothing to do with "myvariable". Debris can land far away from an explosion.
First ,I thank you for your time to resolve my question

In your code except mangle_pointer everything is right.Based in the below now can you please tell why do i get mismatch delete in the valgrind report. It didn't pointing to line no but pointing to function name.



void mangle_pointer(char * & x) {
char *tmp=null;
mp=(char *)x;
}

---------- Post updated at 12:58 PM ---------- Previous update was at 08:58 AM ----------

Now I suspect that is p1 getting the void pointer as a result of called function(Send)?
Inside the Send function get_SendData is assigned with NULL value.

while Send function come to calling function, will this have Null pointer value in the object(p1).
If p1 is void pointer , will this delete p1 work fine?
I am not sure about how to deallocate the void pointer?Despite being searched in the internet ,I still didn't get the clear answer

Code:
void main()
	{
		struct Pack
		{
			unsigned int A;
			unsigned int B;
			unsigned int c;
			unsigned int D;    
		}
		Pack *p1=new Pack;

		Send((void*)p1); 
	//	After calling Send function, what will be the value of p1 pointer . Is it a null pointer since it is asssigned by null poiner in the called function?
	if(p1)
        delete p1;    // Here is the place where i have the doubt that wheher is it expecting to deallocate with free().
 
 
    return 0;
}    
 
bool Send(void* &get_SendData) 
{  
    sendNextLevel(get_SendData)
	
	char* _ucDataCmdReply;
	_ucDataCmdReply = new char[length];
	get_SendData = (void*)_ucDataCmdReply	// Here get_SendData is assigned with void pointer
	
}
     
char* sendNextLevel(void* data)
{
                dataLen = sizeof(PackedSysTime);
 
 
                    Pack* txData = NULL;
                    txData = (Pack*)data;
}

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