从不同的进程设置RichEdit的文本颜色

Question

我正在尝试为来自不同进程的richedit控件（类RichEdit20W）中的特定单词设置背景和前景色。我有使用python调用的以下C代码，但它失败（SendMessage返回0）。如果我将SCF_SELECTION更改为SFC_ALL或0，它可以工作，但遗憾的是它不符合我的需要，因为我只需要将更改应用于控件中的部分文本。

以下是代码：

#include <Windows.h>
#include <stdio.h>
#include <limits.h>
#include <Richedit.h>

__declspec(dllexport) LRESULT SetColour(HWND hWnd, COLORREF textColor, COLORREF bgColor)
{
    CHARRANGE cr;
    cr.cpMin = 3;
    cr.cpMax = 8;

    CHARFORMAT2 cf;
    cf.cbSize = sizeof(cf);
    cf.dwMask = CFM_COLOR | CFM_BACKCOLOR;
    cf.crTextColor = textColor;
    cf.crBackColor = bgColor;

    DWORD   dwPID;
    HANDLE  hProcess;
    LPVOID  pRemoteCR;
    LPVOID  pRemoteCF;
    SIZE_T  zWritten;
    LRESULT lResult;

    GetWindowThreadProcessId(hWnd, &dwPID);
    hProcess = OpenProcess(PROCESS_VM_WRITE | PROCESS_VM_OPERATION, FALSE, dwPID);
    //  Allocate memory on the target process & write the CHARFORMAT2 structure there
    pRemoteCR = VirtualAllocEx(hProcess, NULL, sizeof cr, MEM_COMMIT, PAGE_READWRITE);
    WriteProcessMemory(hProcess, pRemoteCR, &cr, sizeof cr, &zWritten);
    SendMessage(hWnd, EM_EXSETSEL, 0, (LPARAM)pRemoteCR);
    VirtualFreeEx(hProcess, pRemoteCR, 0, MEM_RELEASE);

    pRemoteCF = VirtualAllocEx(hProcess, NULL, sizeof cf, MEM_COMMIT, PAGE_READWRITE);
    WriteProcessMemory(hProcess, pRemoteCF, &cf, sizeof cf, &zWritten);
    lResult = SendMessage(hWnd, EM_SETCHARFORMAT, (WPARAM)SCF_SELECTION, (LPARAM)pRemoteCF); // SCF_SELECTION
    VirtualFreeEx(hProcess, pRemoteCF, 0, MEM_RELEASE);

    return lResult;
}

BOOL WINAPI DllMain(HINSTANCE hinstDLL,DWORD dwReason,LPVOID lpvReserved)
{
    return TRUE;
}