Introduction

Changing proxy settings of IE is a frequent requirement of mine. Then I got the idea of writing a tool by myself, at last. I have not found clear instructions on this. Many articles recommend to modify registry directly, but unfortunately their instruction is not enough. Most of them direct me to modify the following values in registry :-

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

Details

I tested it and find that it does not work at least on my computer.( I access internet by ADSL connection.) So I 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);
        constchar* 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;
        constchar* 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&&NULL!=hk)
    {
        DWORD dwtype;
        char pbuf[256];
        DWORD dwlen=sizeof(pbuf);
        constchar* valname="Connection to adsl3";
        lret=RegQueryValueEx(hk,valname,NULL,&dwtype,pbuf,&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);
    

Existing Internet Explorer instances are notified by INTERNET_OPTION_SETTINGS_CHANGED and INTERNET_OPTION_REFRESH