#define _CRT_SECURE_NO_DEPRECATE //VC++ 2005 mag scheinbar kein fopen :(

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    PSTR szCmdLine, int iCmdShow)
{
    HWND     hWnd;
    MSG      msg;
    WNDCLASS wc;

    const char szAppName[] = "Editcontrol Tutorial";

    wc.style          = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc    = WndProc;
    wc.cbClsExtra     = 0;
    wc.cbWndExtra     = 0;
    wc.hInstance      = hInstance;
    wc.hIcon          = LoadIcon(NULL, IDI_APPLICATION);
    wc.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground  = (HBRUSH)GetStockObject(LTGRAY_BRUSH);
    wc.lpszMenuName   = NULL;
    wc.lpszClassName  = szAppName;

    RegisterClass(&wc);

    hWnd = CreateWindow( szAppName,
                         "Editcontrol Tutorial",
                         WS_OVERLAPPEDWINDOW,
                         CW_USEDEFAULT,
                         CW_USEDEFAULT,
                         CW_USEDEFAULT,
                         CW_USEDEFAULT,
                         NULL,
                         NULL,
                         hInstance,
                         NULL );

    ShowWindow(hWnd, iCmdShow);
    UpdateWindow(hWnd);

    while(GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static HWND hEdit;

    switch(message)
    {
    case WM_CREATE:
        {            
			FILE *fz;
            char *buffer = NULL;
            int iFileSize;

            fz = fopen("text.txt", "rb");
            if(fz != NULL)
            {
                fseek(fz, 0, SEEK_END);
                iFileSize = ftell(fz);
                buffer = malloc(iFileSize);//'void *' kann nicht in 'char *' konvertiert werden

                fseek(fz, 0, SEEK_SET);
                fread(buffer, 1, iFileSize, fz);
                fclose(fz);
            }
			            hEdit = CreateWindowEx(WS_EX_CLIENTEDGE,
                                   "edit",
                                   buffer, 
                                   WS_CHILD | WS_VISIBLE | WS_VSCROLL | ES_MULTILINE |
                                              ES_AUTOVSCROLL,
                                   0, 0, 0, 0,
                                   hWnd,
                                   NULL,
                                   ((LPCREATESTRUCT) lParam) -> hInstance,
                                   NULL);

            free(buffer);

            return 0;
        }
    case WM_SIZE:
        {
			MoveWindow(hEdit, 0, 0, LOWORD(lParam), HIWORD(lParam), TRUE);
            return 0;
        }
    case WM_CLOSE:
        {
			FILE *fz;

			char *buffer = NULL;
            int iLength;

            iLength = GetWindowTextLength(hEdit);

            buffer = malloc(iLength);//'void *' kann nicht in 'char *' konvertiert werden

            GetWindowText(hEdit, buffer, iLength+1);

            fz = fopen("text.txt", "wb");
            fwrite(buffer, 1, iLength, fz);
            fclose(fz);

            free(buffer);

            DestroyWindow(hWnd);
            return 0;
        }
    case WM_DESTROY:
        {
            PostQuitMessage(0);
            return 0;
        }
    }
    return DefWindowProc(hWnd, message, wParam, lParam);
}

Danke schonmal für die Hilfe.

sollte so aussehen

buffer = (char*)malloc(iFileSize);//'void *' kann nicht in 'char *' konvertiert werden

da die funktion malloc ein void* zurückgibt must du es nach char* casten..

außerdem ist das was du hier codest C und kein C++ - schau dir mal String Streams an -> http://www.cppreference.com/cppio/index.html

mfg blan