How to check in C++ if the system is active?

Question

I\'m writing code that need to run only when there is no human activity on the PC, like when the screensaver is running. Any suggestions on how to do this in c++ under windows?<

Answer 1

You can use GetLastInputInfo to check how long the user has been idle (not moved around the mouse or typed something on the keyboard) and SystemParametersInfo to check if a screensaver is active.

Example

#define WINDOWS_LEAN_AND_MEAN
#include 
#include 

// do something after 10 minutes of user inactivity
static const unsigned int idle_milliseconds = 60*10*1000;
// wait at least an hour between two runs
static const unsigned int interval = 60*60*1000;

int main() {
    LASTINPUTINFO last_input;
    BOOL screensaver_active;

    // main loop to check if user has been idle long enough
    for (;;) {
        if ( !GetLastInputInfo(&last_input)
          || !SystemParametersInfo(SPI_GETSCREENSAVERACTIVE, 0,  
                                   &screensaver_active, 0))
        {
            std::cerr << "WinAPI failed!" << std::endl;
            return ERROR_FAILURE;
        }

        if (last_input.dwTime < idle_milliseconds && !screensaver_active) {
            // user hasn't been idle for long enough
            // AND no screensaver is running
            Sleep(1000);
            continue;
        }

        // user has been idle at least 10 minutes
        do_something();
        // done. Wait before doing the next loop.
        Sleep(interval);
    }
}

Note that I wrote that code on a Linux machine, so I couldn't test it.