"To disable the ability to change proxy setting"HOW TO CHANGED PROXY SETTING?

Changing proxy settings of IE. May be this is can little help everything to modify registry directly, in registry:

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings]
"ProxyEnable"=dword:00000001
"ProxyServer"=":"
"ProxyOverride"=""
"DisablePasswordCaching"=dword:00000001

****

We tested it and find that it does not work at least on our computer.(We access internet by ADSL connection.) So We backed up registry and modified proxy settings via Internet Explorer, finding that [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Connections] is also changed. So I wrote the following code snippet to change proxy settings:

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void ShowError(long lerr)
{
LPVOID lpMsgBuf;
if (!FormatMessage(
 FORMAT_MESSAGE_ALLOCATE_BUFFER |
 FORMAT_MESSAGE_FROM_SYSTEM |
 FORMAT_MESSAGE_IGNORE_INSERTS,
 NULL,
 lerr,
 MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
 (LPTSTR) &lpMsgBuf,
 0,
 NULL ))
{
 return;
}
MessageBox( NULL, (LPCTSTR)lpMsgBuf, "Error", MB_OK | MB_ICONINFORMATION );
LocalFree( lpMsgBuf );
}
void CieproxyDlg::OnBnClickedOk()
{//set proxy server
UpdateData();
GetDlgItemText(IDC_EDIT1,m_sIEProxy);
HKEY hk;
LONG lret=RegOpenKeyEx(HKEY_CURRENT_USER,
 "Software\\Microsoft\\Windows\\CurrentVersion\\Internet Settings",
 NULL,KEY_WRITE|KEY_SET_VALUE,&hk);
if(lret==ERROR_SUCCESS&&NULL!=hk)
{
 TCHAR* pbuf=m_sIEProxy.GetBuffer(1);
 lret=RegSetValueEx( hk,"ProxyServer",NULL,REG_SZ,pbuf,m_sIEProxy.GetLength());
 DWORD dwenable=1;
 lret=RegSetValueEx(hk,"ProxyEnable",NULL,REG_DWORD,
    (LPBYTE)&dwenable,sizeof(dwenable));
 RegCloseKey(hk);
}
const TCHAR* keyname3=_T(
"software\\Microsoft\\windows\\currentversion\\Internet Settings\\Connections");
lret=RegOpenKeyEx(HKEY_CURRENT_USER,keyname3,NULL,
 KEY_READ|KEY_WRITE|KEY_SET_VALUE,&hk);
if(lret==ERROR_SUCCESS&&NULL!=hk)
{
 DWORD dwtype;
 char pbuf[256];
 DWORD dwlen=sizeof(pbuf);
 const char* valname="Connection to adsl3";
 lret=RegQueryValueEx(hk,valname,NULL,&dwtype,pbuf,&dwlen);
 if(lret!=ERROR_SUCCESS)
 {
     ShowError(lret);
 }
 pbuf[8] = 3;//enable proxy
 pbuf[4]=pbuf[4]+1;
 const char* p=m_sIEProxy.GetBuffer(1);
 memcpy(pbuf+16,p,m_sIEProxy.GetLength());
 char c=0;
 for(int i=m_sIEProxy.GetLength();i<20;i++)
     pbuf[16+i]=c;
 m_sIEProxy.ReleaseBuffer();
 lret=RegSetValueEx(hk,valname,NULL,REG_BINARY,pbuf,dwlen);
 RegCloseKey(hk);
}
DWORD dwret;
SendMessageTimeout(HWND_BROADCAST,WM_SETTINGCHANGE,NULL,NULL,
 SMTO_NORMAL,1000,&dwret);
}

void CieproxyDlg::OnBnClickedDisableProxy()
{
UpdateData();
GetDlgItemText(IDC_EDIT1,m_sIEProxy);
HKEY hk;
LONG lret=RegOpenKeyEx(HKEY_CURRENT_USER,
 "Software\\Microsoft\\Windows\\CurrentVersion\\Internet Settings",
 NULL,KEY_WRITE|KEY_SET_VALUE,&hk);
if(lret==ERROR_SUCCESS&&NULL!=hk)
{
 DWORD dwenable=0;
 lret=RegSetValueEx(hk,"ProxyEnable",NULL,REG_DWORD,
     (LPBYTE)&dwenable,sizeof(dwenable));
 RegCloseKey(hk);
}
const TCHAR* keyname3=_T(
"software\\Microsoft\\windows\\currentversion\\Internet Settings\\Connections");
lret=RegOpenKeyEx(HKEY_CURRENT_USER,keyname3,
 NULL,KEY_READ|KEY_WRITE|KEY_SET_VALUE,&hk);
if(lret==ERROR_SUCCESS&&amp;amp;amp;amp;amp;amp;NULL!=hk)
{
 DWORD dwtype;
 char pbuf[256];
 DWORD dwlen=sizeof(pbuf);
 const char* valname="Connection to adsl3";
 lret=RegQueryValueEx(hk,valname,NULL,&dwtype,pbuf,&amp;amp;amp;amp;amp;amp;dwlen);
 if(lret!=ERROR_SUCCESS)
 {
     ShowError(lret);
 }
 pbuf[8] = 1;//enable proxy
 pbuf[4]=pbuf[4]+1;
 lret=RegSetValueEx(hk,valname,NULL,REG_BINARY,pbuf,dwlen);
 RegCloseKey(hk);
}
DWORD dwret;
SendMessageTimeout(HWND_BROADCAST,WM_SETTINGCHANGE,NULL,NULL,SMTO_NORMAL,
 1000,&dwret);
}

Problem with above code is that existing Internet Explorer instances don't know the change of settings. What is more, changing registry directly is not an elegant method. Then the following must be more attractive :

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BOOL SetConnectionOptions(LPCTSTR conn_name,LPCTSTR proxy_full_addr)
{
//conn_name: active connection name. 
//proxy_full_addr : eg "210.78.22.87:8000"
INTERNET_PER_CONN_OPTION_LIST list;
BOOL    bReturn;
DWORD   dwBufSize = sizeof(list);
// Fill out list struct.
list.dwSize = sizeof(list);
// NULL == LAN, otherwise connectoid name.
list.pszConnection = conn_name;
// Set three options.
list.dwOptionCount = 3;
list.pOptions = new INTERNET_PER_CONN_OPTION[3];
// Make sure the memory was allocated.
if(NULL == list.pOptions)
{
 // Return FALSE if the memory wasn't allocated.
 OutputDebugString("failed to allocat memory in SetConnectionOptions()");
 return FALSE;
}
// Set flags.
list.pOptions[0].dwOption = INTERNET_PER_CONN_FLAGS;
list.pOptions[0].Value.dwValue = PROXY_TYPE_DIRECT |
 PROXY_TYPE_PROXY;

// Set proxy name.
list.pOptions[1].dwOption = INTERNET_PER_CONN_PROXY_SERVER;
list.pOptions[1].Value.pszValue = proxy_full_addr;//"http://proxy:80";

// Set proxy override.
list.pOptions[2].dwOption = INTERNET_PER_CONN_PROXY_BYPASS;
list.pOptions[2].Value.pszValue = "local";

// Set the options on the connection.
bReturn = InternetSetOption(NULL,
 INTERNET_OPTION_PER_CONNECTION_OPTION, &list, dwBufSize);

// Free the allocated memory.
delete [] list.pOptions;
InternetSetOption(NULL, INTERNET_OPTION_SETTINGS_CHANGED, NULL, 0);
InternetSetOption(NULL, INTERNET_OPTION_REFRESH , NULL, 0);
return bReturn;
}
BOOL DisableConnectionProxy(LPCTSTR conn_name)
{
//conn_name: active connection name. 
INTERNET_PER_CONN_OPTION_LIST list;
BOOL    bReturn;
DWORD   dwBufSize = sizeof(list);
// Fill out list struct.
list.dwSize = sizeof(list);
// NULL == LAN, otherwise connectoid name.
list.pszConnection = conn_name;
// Set three options.
list.dwOptionCount = 1;
list.pOptions = new INTERNET_PER_CONN_OPTION[list.dwOptionCount];
// Make sure the memory was allocated.
if(NULL == list.pOptions)
{
 // Return FALSE if the memory wasn't allocated.
 OutputDebugString("failed to allocat memory in DisableConnectionProxy()");
 return FALSE;
}
// Set flags.
list.pOptions[0].dwOption = INTERNET_PER_CONN_FLAGS;
list.pOptions[0].Value.dwValue = PROXY_TYPE_DIRECT  ;
// Set the options on the connection.
bReturn = InternetSetOption(NULL,
 INTERNET_OPTION_PER_CONNECTION_OPTION, &list, dwBufSize);
// Free the allocated memory.
delete [] list.pOptions;
InternetSetOption(NULL, INTERNET_OPTION_SETTINGS_CHANGED, NULL, 0);
InternetSetOption(NULL, INTERNET_OPTION_REFRESH , NULL, 0);
return bReturn;
}

The usage is very straightforward:

//set proxy
const char* connection_name="Connection to adsl3";
SetConnectionOptions(connection_name,"62.81.236.23:80");
//disable proxy 
DisableConnectionProxy(connection_name);

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