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How to use CopyMemory with integer? API in C++

cuoilennaocacban (9)
I use Shared Memory for communication between 2 processes.

Then I use CopyMemory function to send an array to shared memory, and use it again in the second process to read that array from shared memory.

The problem begin when I try to send just 1 integer to shared memory. I cannot fixed correctly

Here's the error code
 
 
CopyMemory((PVOID)pBuf,n,BUF_SIZE);

n is an integer, contain data (5 for example)
line 72 in first process

and Here's the correct code
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CopyMemory((PVOID)pBuf,a,512*(n+1));
printf("\n\nSending Matrix Information...\n");
getch();

a is an array. a[MAX][MAX], with MAX=100

The full Code
First Process
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#include "stdafx.h"
#include "windows.h"
#include "conio.h"
#include "stdlib.h"

#define MAX 100
#define BUF_SIZE 256

TCHAR MapObjName[]=TEXT("MyFileMappingObject");

void CreateFile(char *FileName, int a[][MAX], int &n);
void ReadFile(char *FileName, int a[][MAX], int n);
void PrintMatrix(int a[][MAX], int n);

int main()
{
	//Usual Task for 2D Array
	int a[MAX][MAX];
	int n=0;
	CreateFile("input.txt",a,n);
	ReadFile("input.txt",a,n);
	PrintMatrix(a,n);
	//END

	//Windows Programming with API
	HANDLE hMapFile;
	LPCTSTR pBuf;

	//Create File Mapping
	hMapFile = CreateFileMapping
		(
		INVALID_HANDLE_VALUE,
		NULL,
		PAGE_READWRITE,
		0,
		BUF_SIZE,
		MapObjName
		);
	//End Create File Mapping

	//Check if creation success
	if(hMapFile == NULL || hMapFile == INVALID_HANDLE_VALUE)
	{
		printf("\nCannot create file mapping: %d",GetLastError());
		exit(1);
	}
	else
		printf("\nCreate File Mapping success!");

	//Map View of File
	pBuf = (LPCTSTR)MapViewOfFile
		(
		hMapFile,
		FILE_MAP_ALL_ACCESS,
		0,
		0,
		BUF_SIZE
		);

	//Check if Create success
	if(pBuf==NULL)
	{
		printf("\nCannot Create Map View of File: %d",GetLastError());
		exit(1);
	}

	//Send Information to shared memory
	CopyMemory((PVOID)pBuf,a,512*(n+1));
	printf("\n\nSending Matrix Information...\n");
	getch();

	CopyMemory((PVOID)pBuf,n,BUF_SIZE);


	UnmapViewOfFile(pBuf);
	CloseHandle(hMapFile);

	//END
	getch();
	return 0;

}

void ReadFile(char *FileName, int a[][MAX], int n)
{
	int temp;
	FILE *File;
	File=fopen(FileName,"r");
	if(File==NULL)
	{
		printf("\nCannot open %s",FileName);
		printf("\nPause Program and Exiting...");
		system("PAUSE");
		exit(-1);
	}
	fscanf(File,"%d",&n);
	for(int i=0;i<n;i++)
		for(int j=0;j<n;j++)
		{
			fscanf(File,"%d",&temp);
			a[i][j]=temp;
		}
	fclose(File);
}

void CreateFile(char *FileName, int a[][MAX], int &n)
{
	FILE *f;
	int ran; //Create Random Matrix
	printf("\n Enter the size of Matrix: ");
	scanf("%d",&n);
	printf("\nDo you want program automatically create a matrix? 1/0: ");
	scanf("%d",&ran);
	if(ran==1)
	{
		for(int i=0;i<n;i++)
			for(int j=0;j<n;j++)
				a[i][j]=rand();
		f=fopen(FileName,"w");
		fprintf(f,"%d",n); //Print size of Matrix
		fprintf(f,"\n");
		for(int i=0;i<n;i++)
		{
			for(int j=0;j<n;j++)
				fprintf(f,"%10d",a[i][j]);
			fprintf(f,"\n");
		}
		fclose(f);
	}
	else
	{
		printf("\nEnter your Matrix\n");
		f=fopen(FileName,"w");
		fprintf(f,"%d",n); //Print the size of Matrix
		fprintf(f,"\n");
		for(int i=0;i<n;i++)
		{
			for(int j=0;j<n;j++)
			{
				printf("Column [%d] - Row [%d]: ",i,j);
				scanf("%d",&a[i][j]);
				fprintf(f,"%10d",a[i][j]);
			}
			fprintf(f,"\n");
		}
		fclose(f);
	}
}

void PrintMatrix(int a[][MAX], int n)
{
	printf("\nMatrix\n");
	for(int i=0;i<n;i++)
	{
		for(int j=0;j<n;j++)
			printf("%10d",a[i][j]);
		printf("\n");
	}
}



The Second Process
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#include "stdafx.h"
#include "windows.h"
#include "conio.h"
#include "stdlib.h"

#define BUF_SIZE 256
#define MAX 100
TCHAR szName[]=TEXT("MyFileMappingObject");
TCHAR size[]=TEXT("SizeOfMatrix");

void PrintMatrix(int a[][MAX], int n);

int main()
{
	HANDLE hMapFile;
	HANDLE hSize;
	LPCTSTR pBuf;
	LPCTSTR pSize;

	hMapFile = OpenFileMapping
		(
		FILE_MAP_ALL_ACCESS, //Read,write access
		FALSE, //do not inherit the name
		szName //name of mapping object
		);

	if(hMapFile==NULL)
	{
		printf("\nCould not open file mapping object: %d\n",GetLastError());
		return 0;
	}

	pBuf = (LPCTSTR) MapViewOfFile
		(
		hMapFile,
		FILE_MAP_ALL_ACCESS,
		0,
		0,
		BUF_SIZE
		);

	if (pBuf== NULL)
	{
		printf("Could not map view of file: %d\n", GetLastError());
		return 0;
	}

	int a[MAX][MAX];
	int n;

	n=6;

	printf("\nReceiving Matrix Information...\n");
	CopyMemory(a,(PVOID)pBuf,512*n);
	getch();

	PrintMatrix(a,n);
	return 0;
}

void PrintMatrix(int a[][MAX], int n)
{
	printf("\nMatrix\n");
	for(int i=0;i<n;i++)
	{
		for(int j=0;j<n;j++)
			printf("%10d",a[i][j]);
		printf("\n");
	}
}


I look for this CopyMemory function on MSDN, not help very much
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Syntax

void CopyMemory(
  __in  PVOID Destination,
  __in  const VOID *Source,
  __in  SIZE_T Length
);

Parameters

Destination [in]

    A pointer to the starting address of the copied block's destination.
Source [in]

    A pointer to the starting address of the block of memory to copy.
Length [in]

    The size of the block of memory to copy, in bytes.

Return value

This function has no return value.
coder777 (8439)
This: CopyMemory((PVOID)pBuf,&n,BUF_SIZE); // Notice the & before n is the short solution

and Here's the correct code
No! BUF_SIZE is 256 bytes. You're trying to copy 512 bytes that should lead to an access violation.

By the way: you don't need to cast to (PVOID) since PVOID accepts all pointers to non const objects.

I'd recommend to use a struct instead of 'LPCTSTR pBuf'

Like so: 
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struct D
{
	int a[MAX][MAX];
	int n=0;
};
...

hMapFile = CreateFileMapping
		(
		INVALID_HANDLE_VALUE,
		NULL,
		PAGE_READWRITE,
		0,
		sizeof(D), // Note sizeof()
		MapObjName
		);

...

D *d = (D *)MapViewOfFile
		(
		hMapFile,
		FILE_MAP_ALL_ACCESS,
		0,
		0,
		sizeof(D), // Note sizeof()
		);

...

d->n = 5;


The second process accordingly. The need a shared header file with the definition of D (or whatever you want to name it). So you don't need that dangarous CopyMemory().
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