TCHAR *teststr = L"mon.dll\x00url";

    TCHAR *newstr;
    newstr = (TCHAR*)halloc(sizeof(TCHAR)*12);

    lstrcpy(newstr, teststr+lstrlen(teststr)+1);
    lstrcat(newstr, teststr);
    lstrcpy(teststr, newstr);

    OutputDebugString(L"Test: ");
    OutputDebugString(teststr);
    OutputDebugString(L"\n");
    hfree(newstr);

Output:
First-chance exception at 0x767a2733 in suckblow.exe: 0xC0000005: Access violation writing location 0x010c203c.
Test: mon.dll