memory leaks

[THEARTOFWEB]

Hi,

do you think the following code could lead to memory leaks?

#define _CRT_SECURE_NO_WARNINGS
#include <windows.h>
#include <vector>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <boost/circular_buffer.hpp>
using namespace std;
using namespace boost;

char * getDateTime(void);
const short numbuff = 5;
const short buflen  = 30;

typedef struct
{
	unsigned char * pData;
	unsigned short bufferLength;
	unsigned short bytesRecorded;
	bool flag;
} Buffer;

int main()
{
	circular_buffer<Buffer*> cb(numbuff);
	circular_buffer<Buffer*>::const_iterator it;

	// fill buffer
	for(int i = 0; i<numbuff; i++)
	{
		// set up buffer
		Buffer *buff       = new Buffer;
		ZeroMemory(buff, sizeof(Buffer));

		buff->bufferLength  = buflen;
		buff->bytesRecorded = buflen;
		buff->flag          = true;
		buff->pData         = new unsigned char[buflen];
		buff->pData         = reinterpret_cast<unsigned char *>(getDateTime());

		// push buffer
		cb.push_back(buff);

		Sleep(1000);
	}

	// show elements

	for(int i = 0; i<(int)cb.size(); i++)
	{
		printf("%s\n", cb[i]->pData);
	}

	system("pause");
	return EXIT_SUCCESS;
}

// getDateTime (Fri, 10 Oct 2008 14:41:59 GMT)
char * getDateTime(void)
{
	time_t rawtime;
	struct tm * timeinfo;
	time(&rawtime);
	timeinfo = gmtime(&rawtime);
	char * buffer = new char[30];
	strftime(buffer,30,"%a, %d %b %Y %X GMT",timeinfo);
	return buffer;
}

I cannot delete "buff" since its scope is inside the first for loop...

[THEARTOFWEB]

Hi,

do you think the following code could lead to memory leaks? it creates a
circualr buffer made up of 5 element then it pushes 10 elements (overwriting
the first 5) when overwriting , do you think the eldest pointed memory will
be overwritten, or a new pointer in memory will be written?

#define _CRT_SECURE_NO_WARNINGS
#include <windows.h>
#include <vector>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <boost/circular_buffer.hpp>
using namespace std;
using namespace boost;

char * getDateTime(void);
const short numbuff = 5;
const short buflen  = 30;

typedef struct
{
 unsigned char * pData;
 unsigned short bufferLength;
 unsigned short bytesRecorded;
 bool flag;
} Buffer;

int main()
{
 circular_buffer<Buffer*> cb(numbuff);
 circular_buffer<Buffer*>::const_iterator it;

 printf("Push elements:\n");
 // fill buffer
 for(int i = 0; i<10; i++)
 {
  // set up buffer
  Buffer *buff       = new Buffer;
  ZeroMemory(buff, sizeof(Buffer));

  buff->bufferLength  = buflen;
  buff->bytesRecorded = buflen;
  buff->flag          = true;
  buff->pData         = new unsigned char[buflen];
  buff->pData         = reinterpret_cast<unsigned char *>(getDateTime());

  printf("%s\n", buff->pData);

  // push buffer
  cb.push_back(buff);

  Sleep(1000);
 }

 printf("\nShow elements:\n");

 // show elements
 for(int i = 0; i<static_cast<int>(cb.size()); i++)
 {
  printf("%s\n", cb[i]->pData);
 }

 system("pause");
 return EXIT_SUCCESS;
}

// getDateTime (Fri, 10 Oct 2008 14:41:59 GMT)
char * getDateTime(void)
{
 time_t rawtime;
 struct tm * timeinfo;
 time(&rawtime);
 timeinfo = gmtime(&rawtime);
 char * buffer = new char[30];
 strftime(buffer,30,"%a, %d %b %Y %X GMT",timeinfo);
 return buffer;
}

// thanks

[Skizmo]

buff->pData = new unsigned char[buflen];
buff->pData = reinterpret_cast<unsigned char *>(getDateTime());

This leaks. pData is overwritten the 2nd time so the memory you created the 1st time is gone.
Also... who frees the memory that 'getDateTime' has created.

[VictorN]

All that you newed you *must* delete. Period.
If you don't delete what you have newed then you produce memory leaks.

[THEARTOFWEB]

This leaks. pData is overwritten the 2nd time so the memory you created the 1st time is gone.
Also... who frees the memory that 'getDateTime' has created.

by the way, how can I change getDateTime() to return char[30] ?? I mean the return type...

thanks

[THEARTOFWEB]

All that you newed you *must* delete. Period.
If you don't delete what you have newed then you produce memory leaks.

Ok. As I was suggested in this very forum...I am going to use vector to collect chars...is that ok? and no pointers anymore...

[VictorN]

by the way, how can I change getDateTime() to return char[30] ?? I mean the return type...

thanks

For example:

 void getDateTime( char *buffer)
{
 time_t rawtime;
 struct tm * timeinfo;
 time(&rawtime);
 timeinfo = gmtime(&rawtime);

 strftime(buffer,30,"%a, %d %b %Y %X GMT",timeinfo);
}

Now you can:

char buffer[30];
getDateTime(buffer);

[VictorN]

...I am going to use vector to collect chars...is that ok? and no pointers anymore...

Yes, it is definetly a very good idea!

[THEARTOFWEB]

For instance...do you think the following could be better approach?

struct Buffer
{
public:
	vector<unsigned char> vChar;
	unsigned int bufferLength;
	unsigned int bytesRecorded;
	Buffer() : bytesRecorded(0), bufferLength(0), vChar(NULL) { };
};

int main()
{
	circular_buffer<Buffer> cb(numbuff);
	circular_buffer<Buffer>::const_iterator it;

	(...)
}

thanks

[THEARTOFWEB]

anyway, I have a problem with assign a char to a vector:

void getDateTime(char * szTime);
const int numbuff = 5;
const int buflen  = 30;

struct Buffer
{
public:
	vector<char> vChar;
	unsigned int bufferLength;
	unsigned int bytesRecorded;
	Buffer() : bytesRecorded(0), bufferLength(0), vChar(NULL) { };
};

int main()
{
	circular_buffer<Buffer> cb(numbuff);
	circular_buffer<Buffer>::const_iterator it;

	for(int i = 0; i<10; i++)
	{
		// Get time
		char szTime[30]; getDateTime(szTime);

		// Init Buff
		Buffer buff;
		ZeroMemory(&buff, sizeof(Buffer));

		buff.vChar.resize(buflen);
		buff.vChar         = szTime;
		buff.bufferLength  = buflen;
		buff.bytesRecorded = buflen;

		printf("%s\n", buff.vChar);
	}

	system("pause");
	return EXIT_SUCCESS;
}

// getDateTime (Fri, 10 Oct 2008 14:41:59 GMT)
void getDateTime(char * szTime)
{
	time_t rawtime = time(NULL);
	struct tm timeinfo;
	gmtime_s(&timeinfo, &rawtime);
	strftime(szTime, 30, "%a, %d %b %Y %X GMT", &timeinfo);
}

the code fails here:

buff.vChar = szTime;

why?

thanks

[VictorN]

Because szTime is not a char

[THEARTOFWEB]

do you mean szTime is several chars ??

[VictorN]

No, it is a pointer to a NULL-terminated string (character array)

[THEARTOFWEB]

well, I thought this was a stand-alone string (chars array) not a pointer:

char szTime[30]; getDateTime(szTime);

I tried using memcpy but it's not working...

[Paul McKenzie]

well, I thought this was a stand-alone string (chars array) not a pointer:

char szTime[30]; getDateTime(szTime);

I tried using memcpy but it's not working...

First, change the function getDateTime() to return a string, not a char*.

// getDateTime (Fri, 10 Oct 2008 14:41:59 GMT)
std::string getDateTime(void)
{
   time_t rawtime;
   struct tm * timeinfo;
   time(&rawtime);
   timeinfo = gmtime(&rawtime);
   char buffer[30];
   strftime(buffer,30,"%a, %d %b %Y %X GMT",timeinfo);
   return buffer;
}

There really isn't a reason to resort to char* and new[] to create strings in a C++ application.

Regards,

Paul McKenzie