Windows hook using windows api in QT

**davinciomare** · 4th October 2016, 22:59

Hi i am searching for windows hook and i checked this in the webpage of microsoft. But i dont know how i can't return the value since function using LRESULT to show for example since qDebug the key pressed for me in terminal.
Error:
C:\Users\moh\Documents\Hook\main.cpp:63: error: C2440: 'return' : no se puede realizar la conversiÂ¢n de 'QString' a 'LRESULT' No hay disponible ningÂ£n operador de conversiÂ¢n definido por el usuario que pueda realizar esta conversiÂ¢n, o bien no se puede llamar al operador

The question is how i can change the returned value to Qstring. It's only for doing one example with qDebug thx

**d_stranz** · 5th October 2016, 01:24

LRESULT is just a long. Read the QString documentation for how to convert integers into printable strings.

**davinciomare** · 5th October 2016, 01:51

I know how to convert i need to use this:
QString tmp = QString::number();

But i have one more question related with this, i want to return the value for learning and then show with qdebug but i couldnt. Code:

Qt Code:

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#include <QCoreApplication>
#include <QDebug>
#include <QTime>
#include <QChar>
#include <iostream>
#include <Windows.h>
#pragma comment(lib,"user32.lib")
 
HHOOK hHook = NULL;
 
using namespace std;
 
void UpdateKeyState(BYTE *keystate, int keycode)
{
    keystate[keycode] = GetKeyState(keycode);
}
 
LRESULT CALLBACK MyLowLevelKeyBoardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
 
    //WPARAM is WM_KEYDOWN, WM_KEYUP, WM_SYSKEYDOWN or WM_SYSKEYUP
    //LPARAM is the key information
   // if( wParam == WM_KEYDOWN )
        //qDebug() << "Key Pressed!";
 
    //Get the key information
 
    KBDLLHOOKSTRUCT cKey = *((KBDLLHOOKSTRUCT*)lParam);
 
    wchar_t buffer[5];
 
    //get the keyboard state
    BYTE keyboard_state[256];
    GetKeyboardState(keyboard_state);
    UpdateKeyState(keyboard_state, VK_SHIFT);
    UpdateKeyState(keyboard_state, VK_CAPITAL);
    UpdateKeyState(keyboard_state, VK_CONTROL);
    UpdateKeyState(keyboard_state, VK_MENU);
 
 
 
    //Get Keyboard Layout
    HKL keyboard_layout = GetKeyboardLayout(0);
 
    //Get the name
    char lpszName[0x100] = {0};
 
    DWORD dwMsg = 1;
    dwMsg += cKey.scanCode << 16;
    dwMsg += cKey.flags << 24;
 
    int i = GetKeyNameText(dwMsg, (LPTSTR)lpszName,255);
    //try to convert the key info
    int result = ToUnicodeEx(cKey.vkCode, cKey.scanCode, keyboard_state, buffer,4,0, keyboard_layout);
    buffer[4] = L'\0';
    //qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
    int num = cKey.vkCode;
    // Print the output
 
    if( wParam == WM_KEYDOWN )
        //qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
        return num;
 
 
    return CallNextHookEx(hHook, nCode, wParam, lParam);
}
 
int main(int argc, char *argv[])
{
 
    QCoreApplication a(argc, argv);
 
    hHook = SetWindowsHookEx(WH_KEYBOARD_LL, MyLowLevelKeyBoardProc, NULL,0);
    if(hHook == NULL){
        qDebug() << "error";
    }
    QString tmp = QString::number(num);
 
    return a.exec();
}

#include <QCoreApplication>
#include <QDebug>
#include <QTime>
#include <QChar>
#include <iostream>
#include <Windows.h>
#pragma comment(lib,"user32.lib")

HHOOK hHook = NULL;

using namespace std;

void UpdateKeyState(BYTE *keystate, int keycode)
{
    keystate[keycode] = GetKeyState(keycode);
}

LRESULT CALLBACK MyLowLevelKeyBoardProc(int nCode, WPARAM wParam, LPARAM lParam)
{

    //WPARAM is WM_KEYDOWN, WM_KEYUP, WM_SYSKEYDOWN or WM_SYSKEYUP
    //LPARAM is the key information
   // if( wParam == WM_KEYDOWN )
        //qDebug() << "Key Pressed!";

    //Get the key information

    KBDLLHOOKSTRUCT cKey = *((KBDLLHOOKSTRUCT*)lParam);

    wchar_t buffer[5];

    //get the keyboard state
    BYTE keyboard_state[256];
    GetKeyboardState(keyboard_state);
    UpdateKeyState(keyboard_state, VK_SHIFT);
    UpdateKeyState(keyboard_state, VK_CAPITAL);
    UpdateKeyState(keyboard_state, VK_CONTROL);
    UpdateKeyState(keyboard_state, VK_MENU);



    //Get Keyboard Layout
    HKL keyboard_layout = GetKeyboardLayout(0);

    //Get the name
    char lpszName[0x100] = {0};

    DWORD dwMsg = 1;
    dwMsg += cKey.scanCode << 16;
    dwMsg += cKey.flags << 24;

    int i = GetKeyNameText(dwMsg, (LPTSTR)lpszName,255);
    //try to convert the key info
    int result = ToUnicodeEx(cKey.vkCode, cKey.scanCode, keyboard_state, buffer,4,0, keyboard_layout);
    buffer[4] = L'\0';
    //qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
    int num = cKey.vkCode;
    // Print the output

    if( wParam == WM_KEYDOWN )
        //qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
        return num;


    return CallNextHookEx(hHook, nCode, wParam, lParam);
}

int main(int argc, char *argv[])
{

    QCoreApplication a(argc, argv);

    hHook = SetWindowsHookEx(WH_KEYBOARD_LL, MyLowLevelKeyBoardProc, NULL,0);
    if(hHook == NULL){
        qDebug() << "error";
    }
    QString tmp = QString::number(num);

    return a.exec();
}

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It's only for doing one example with qdebug of the webpage of microsoft. sorry again..

**d_stranz** · 5th October 2016, 05:49

I have no idea what you are trying to do. YOUR CODE IS UNREADABLE. FOR THE LAST TIME, USE [CODE] TAGS.

**davinciomare** · 5th October 2016, 09:19

what is code tags? where are?

**Lesiok** · 5th October 2016, 09:41

Originally Posted by davinciomare

what is code tags? where are?

Please use CODE tags when posting source code so it is more readable. Click "Go Advanced" and then the "#" icon to insert the tags. Paste your code between them.

**davinciomare** · 5th October 2016, 09:50

Sorry i will not repeat this mistake again.

Qt Code:

Switch view

#include <QCoreApplication>
#include <QDebug>
#include <QTime>
#include <QChar>
#include <iostream>
#include <Windows.h>
#pragma comment(lib,"user32.lib")
 
HHOOK hHook = NULL;
 
using namespace std;
 
void UpdateKeyState(BYTE *keystate, int keycode)
{
keystate[keycode] = GetKeyState(keycode);
}
 
LRESULT CALLBACK MyLowLevelKeyBoardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
 
//WPARAM is WM_KEYDOWN, WM_KEYUP, WM_SYSKEYDOWN or WM_SYSKEYUP
//LPARAM is the key information
// if( wParam == WM_KEYDOWN )
//qDebug() << "Key Pressed!";
 
//Get the key information
 
KBDLLHOOKSTRUCT cKey = *((KBDLLHOOKSTRUCT*)lParam);
 
wchar_t buffer[5];
 
//get the keyboard state
BYTE keyboard_state[256];
GetKeyboardState(keyboard_state);
UpdateKeyState(keyboard_state, VK_SHIFT);
UpdateKeyState(keyboard_state, VK_CAPITAL);
UpdateKeyState(keyboard_state, VK_CONTROL);
UpdateKeyState(keyboard_state, VK_MENU);
 
 
 
//Get Keyboard Layout
HKL keyboard_layout = GetKeyboardLayout(0);
 
//Get the name
char lpszName[0x100] = {0};
 
DWORD dwMsg = 1;
dwMsg += cKey.scanCode << 16;
dwMsg += cKey.flags << 24;
 
int i = GetKeyNameText(dwMsg, (LPTSTR)lpszName,255);
//try to convert the key info
int result = ToUnicodeEx(cKey.vkCode, cKey.scanCode, keyboard_state, buffer,4,0, keyboard_layout);
buffer[4] = L'\0';
//qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
int num = cKey.vkCode;
// Print the output
 
if( wParam == WM_KEYDOWN )
//qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
return num;
 
 
return CallNextHookEx(hHook, nCode, wParam, lParam);
}
 
int main(int argc, char *argv[])
{
 
QCoreApplication a(argc, argv);
 
hHook = SetWindowsHookEx(WH_KEYBOARD_LL, MyLowLevelKeyBoardProc, NULL,0);
if(hHook == NULL){
qDebug() << "error";
}
QString tmp = QString::number(num);
 
return a.exec();
}

#include <QCoreApplication>
#include <QDebug>
#include <QTime>
#include <QChar>
#include <iostream>
#include <Windows.h>
#pragma comment(lib,"user32.lib")

HHOOK hHook = NULL;

using namespace std;

void UpdateKeyState(BYTE *keystate, int keycode)
{
keystate[keycode] = GetKeyState(keycode);
}

LRESULT CALLBACK MyLowLevelKeyBoardProc(int nCode, WPARAM wParam, LPARAM lParam)
{

//WPARAM is WM_KEYDOWN, WM_KEYUP, WM_SYSKEYDOWN or WM_SYSKEYUP
//LPARAM is the key information
// if( wParam == WM_KEYDOWN )
//qDebug() << "Key Pressed!";

//Get the key information

KBDLLHOOKSTRUCT cKey = *((KBDLLHOOKSTRUCT*)lParam);

wchar_t buffer[5];

//get the keyboard state
BYTE keyboard_state[256];
GetKeyboardState(keyboard_state);
UpdateKeyState(keyboard_state, VK_SHIFT);
UpdateKeyState(keyboard_state, VK_CAPITAL);
UpdateKeyState(keyboard_state, VK_CONTROL);
UpdateKeyState(keyboard_state, VK_MENU);



//Get Keyboard Layout
HKL keyboard_layout = GetKeyboardLayout(0);

//Get the name
char lpszName[0x100] = {0};

DWORD dwMsg = 1;
dwMsg += cKey.scanCode << 16;
dwMsg += cKey.flags << 24;

int i = GetKeyNameText(dwMsg, (LPTSTR)lpszName,255);
//try to convert the key info
int result = ToUnicodeEx(cKey.vkCode, cKey.scanCode, keyboard_state, buffer,4,0, keyboard_layout);
buffer[4] = L'\0';
//qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
int num = cKey.vkCode;
// Print the output

if( wParam == WM_KEYDOWN )
//qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
return num;


return CallNextHookEx(hHook, nCode, wParam, lParam);
}

int main(int argc, char *argv[])
{

QCoreApplication a(argc, argv);

hHook = SetWindowsHookEx(WH_KEYBOARD_LL, MyLowLevelKeyBoardProc, NULL,0);
if(hHook == NULL){
qDebug() << "error";
}
QString tmp = QString::number(num);

return a.exec();
}

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I want to return for example num of LRESULT function and print with qdebug since main or something like that.

**Lesiok** · 5th October 2016, 11:51

I think that this is not a version of the code with which you write in the first post. Line 63 is empty.

**davinciomare** · 5th October 2016, 12:09

When i use const char* to print with qdebug the program crash.
Code:

Qt Code:

Switch view

#include <QCoreApplication>
#include <QDebug>
#include <QTime>
#include <QChar>
#include <iostream>
#include <QFile>
#include <QString>
#include <Windows.h>
#pragma comment(lib,"user32.lib")
 
HHOOK hHook = NULL;
 
using namespace std;
 
QByteArray contenido="Estoy escribiendo a un archivo";
QFile ap("C:/Users/moh/Desktop/documento.txt");
QString ok;
 
void UpdateKeyState(BYTE *keystate, int keycode)
{
    keystate[keycode] = GetKeyState(keycode);
}
 
LRESULT CALLBACK MyLowLevelKeyBoardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    QFile ap("C:/Users/moh/Desktop/documento.txt");
 
 
    //WPARAM is WM_KEYDOWN, WM_KEYUP, WM_SYSKEYDOWN or WM_SYSKEYUP
    //LPARAM is the key information
   // if( wParam == WM_KEYDOWN )
        //qDebug() << "Key Pressed!";
 
    //Get the key information
 
    KBDLLHOOKSTRUCT cKey = *((KBDLLHOOKSTRUCT*)lParam);
 
    wchar_t buffer[5];
 
    //get the keyboard state
    BYTE keyboard_state[256];
    GetKeyboardState(keyboard_state);
    UpdateKeyState(keyboard_state, VK_SHIFT);
    UpdateKeyState(keyboard_state, VK_CAPITAL);
    UpdateKeyState(keyboard_state, VK_CONTROL);
    UpdateKeyState(keyboard_state, VK_MENU);
 
 
 
    //Get Keyboard Layout
    HKL keyboard_layout = GetKeyboardLayout(0);
 
    //Get the name
    char lpszName[0x100] = {0};
 
    DWORD dwMsg = 1;
    dwMsg += cKey.scanCode << 16;
    dwMsg += cKey.flags << 24;
 
    int i = GetKeyNameText(dwMsg, (LPTSTR)lpszName,255);
    //try to convert the key info
    int result = ToUnicodeEx(cKey.vkCode, cKey.scanCode, keyboard_state, buffer,4,0, keyboard_layout);
    buffer[4] = L'\0';
    //qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
    QString num = QString::fromUtf16((ushort*)buffer);
    // Print the output
 
    int cod = cKey.vkCode;
 
    if( wParam == WM_KEYDOWN ){
        //qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
        ap.open(QIODevice::WriteOnly | QIODevice::Text);
        ap.write((const char*)result);
        ap.close();
 
 
 
    }
 
    return CallNextHookEx(hHook, nCode, wParam, lParam);
 
 
}
 
int main(int argc, char *argv[])
{
 
    QCoreApplication a(argc, argv);
 
 
    hHook = SetWindowsHookEx(WH_KEYBOARD_LL, MyLowLevelKeyBoardProc, NULL,0);
    if(hHook == NULL){
        qDebug() << "error";
    }
 
    /*
       if(!ap.exists()){
        qDebug() << "El archivo seleccionado no existe";
        return 1;
    }
    ap.open(QIODevice::WriteOnly | QIODevice::Text);
    if (!ap.isOpen()){
        qDebug() << "El archivo no se ha podido abrir";
        return 2;
    }
    //contenido = ap.readAll();
    ap.write(contenido);
    ap.flush();
    ap.close();
*/
 
    return a.exec();
}

#include <QCoreApplication>
#include <QDebug>
#include <QTime>
#include <QChar>
#include <iostream>
#include <QFile>
#include <QString>
#include <Windows.h>
#pragma comment(lib,"user32.lib")

HHOOK hHook = NULL;

using namespace std;

QByteArray contenido="Estoy escribiendo a un archivo";
QFile ap("C:/Users/moh/Desktop/documento.txt");
QString ok;

void UpdateKeyState(BYTE *keystate, int keycode)
{
    keystate[keycode] = GetKeyState(keycode);
}

LRESULT CALLBACK MyLowLevelKeyBoardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    QFile ap("C:/Users/moh/Desktop/documento.txt");


    //WPARAM is WM_KEYDOWN, WM_KEYUP, WM_SYSKEYDOWN or WM_SYSKEYUP
    //LPARAM is the key information
   // if( wParam == WM_KEYDOWN )
        //qDebug() << "Key Pressed!";

    //Get the key information

    KBDLLHOOKSTRUCT cKey = *((KBDLLHOOKSTRUCT*)lParam);

    wchar_t buffer[5];

    //get the keyboard state
    BYTE keyboard_state[256];
    GetKeyboardState(keyboard_state);
    UpdateKeyState(keyboard_state, VK_SHIFT);
    UpdateKeyState(keyboard_state, VK_CAPITAL);
    UpdateKeyState(keyboard_state, VK_CONTROL);
    UpdateKeyState(keyboard_state, VK_MENU);



    //Get Keyboard Layout
    HKL keyboard_layout = GetKeyboardLayout(0);

    //Get the name
    char lpszName[0x100] = {0};

    DWORD dwMsg = 1;
    dwMsg += cKey.scanCode << 16;
    dwMsg += cKey.flags << 24;

    int i = GetKeyNameText(dwMsg, (LPTSTR)lpszName,255);
    //try to convert the key info
    int result = ToUnicodeEx(cKey.vkCode, cKey.scanCode, keyboard_state, buffer,4,0, keyboard_layout);
    buffer[4] = L'\0';
    //qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
    QString num = QString::fromUtf16((ushort*)buffer);
    // Print the output

    int cod = cKey.vkCode;

    if( wParam == WM_KEYDOWN ){
        //qDebug() << "key:" << cKey.vkCode << " " << QString::fromUtf16((ushort*)buffer) << " " << QString::fromUtf16((ushort*)lpszName);
        ap.open(QIODevice::WriteOnly | QIODevice::Text);
        ap.write((const char*)result);
        ap.close();



    }

    return CallNextHookEx(hHook, nCode, wParam, lParam);


}

int main(int argc, char *argv[])
{

    QCoreApplication a(argc, argv);


    hHook = SetWindowsHookEx(WH_KEYBOARD_LL, MyLowLevelKeyBoardProc, NULL,0);
    if(hHook == NULL){
        qDebug() << "error";
    }

    /*
       if(!ap.exists()){
        qDebug() << "El archivo seleccionado no existe";
        return 1;
    }
    ap.open(QIODevice::WriteOnly | QIODevice::Text);
    if (!ap.isOpen()){
        qDebug() << "El archivo no se ha podido abrir";
        return 2;
    }
    //contenido = ap.readAll();
    ap.write(contenido);
    ap.flush();
    ap.close();
*/

    return a.exec();
}

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Basically the problem is here:
ap.write((const char*)cod);

When i write this the program crash. And i can't return other values only 4 arguments since MyLowLevelKeyBoardProc. Some way to return my key pressed is for learning?

**Lesiok** · 5th October 2016, 13:13

You do not necessarily know what you're doing. "(const char*)cod" is the "cod variable contains the address." I do not think the variable cod was a pointer to memory.
I guess you must first learn the basics of C ++ and later use libraries as powerful as Qt

**davinciomare** · 5th October 2016, 14:13

yes i am not very well in c++ but i was searching and you right a lot of documentation about this so it's right. thx solved

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