fwrite()库函数为什么会吃内存？

/************************************************

 * test.cpp

 ************************************************/

 

#include "./FileClass.h"

#include "../type.h"

#include <unistd.h>

#include <sys/sysinfo.h>

#include <sys/types.h>



#define FWRITE_BUFFER_LENGTH 400*1024

int main(void)

{

    CFile cInFile;

	CFile cOutFile;

	char* bfTemp = new char[400000];

	char* bfFwrite = new char[FWRITE_BUFFER_LENGTH];

	unsigned int uiFileLength=0;

	unsigned int uiReadFileLength=0;

	unsigned int uiOutFileIndex=1;

	char szOutFileName[MAX_FILENAME_LENGTH];

	struct sysinfo MySysinfo;

	int iRet;

	

	cInFile.SetFullFileName("./In.jpg");

	cInFile.Open(BINARY_RWTYPE,POS_START);

	uiFileLength = cInFile.GetFileLength();

	uiFileLength = 314890;

	iRet = cInFile.Read(bfTemp, uiFileLength, uiReadFileLength);

	if(iRet==0 && uiFileLength==uiReadFileLength)

	{

	    printf("== Read input file successfully\n");

	}

	else

	{

	    printf("== Read input file failed\n== Read() return %d; File length is %d; Read number is %d\n",iRet,uiFileLength,uiReadFileLength);

		return -1;

	}

	while(1)

	{

	    snprintf(szOutFileName,MAX_FILENAME_LENGTH,"/EpData/OutFile%d.jpg",uiOutFileIndex++);

		cOutFile.SetFullFileName(szOutFileName);

		iRet = cOutFile.Open(BINARY_RWTYPE,POS_START);

		//cOutFile.SetFwriteNoBuffer( );

		if(iRet < 0)

		{

		    printf("== cOutFile.Open() failed\n");

			break;

		}

		iRet = cOutFile.Write(bfTemp,uiFileLength);

		if(iRet < 0)

		{

		    cOutFile.Close();

		    break;

		}

		cOutFile.Close();

		sysinfo(&MySysinfo);

		printf("== Free memory is %ldK\n",MySysinfo.freeram/1024);

		sleep(1);

	}



	delete[] bfTemp;

	delete[] bfFwrite;

	cInFile.Close();



    return 0;

}