CODEWITHSUNDEEP
c++windowsmsdnmultiple-monitors
annie1994
annie1994

Reputation: 143

EnumDisplayDevices does not return any value

I am trying to enumerate details of all monitors connected on a multi-monitor system. So I refered to this sample code. Here is the complete code for reference:

#include <windows.h>
#include <stdio.h>

#pragma comment(lib, "user32.lib")

void DumpDevice(const DISPLAY_DEVICE& dd, size_t nSpaceCount )
{
    printf("%*sDevice Name: %s\n", nSpaceCount, "", dd.DeviceName );
    printf("%*sDevice String: %s\n", nSpaceCount, "", dd.DeviceString );
    printf("%*sState Flags: %x\n", nSpaceCount, "", dd.StateFlags );
    printf("%*sDeviceID: %s\n", nSpaceCount, "", dd.DeviceID );
    printf("%*sDeviceKey: ...%s\n\n", nSpaceCount, "", dd.DeviceKey+42 );
}

int main()
{
    DISPLAY_DEVICE dd;

    dd.cb = sizeof(DISPLAY_DEVICE);

    DWORD deviceNum = 0;
    while( EnumDisplayDevices(NULL, deviceNum, &dd, 0) ){
        DumpDevice( dd, 0 );
        DISPLAY_DEVICE newdd = {0};
        newdd.cb = sizeof(DISPLAY_DEVICE);
        DWORD monitorNum = 0;
        while ( EnumDisplayDevices(dd.DeviceName, monitorNum, &newdd, 0))
        {
            DumpDevice( newdd, 4 );
            monitorNum++;
        }
        puts("");
        deviceNum++;
    }

    return 0;
}

However when I run this code, it returns this:

Device Name: \
Device String: N
State Flags: 5
DeviceID: P
DeviceKey: ...\

   Device Name: \
   Device String: V
   State Flags: 3
   DeviceID: M
   DeviceKey: ...\

Device Name: \
Device String: N
State Flags: 1
DeviceID: P
DeviceKey: ...\

Device Name: \
Device String: G
State Flags: 3
DeviceID: M
DeviceKey: ...\

Device Name: \
Device String: N
State Flags: 0
DeviceID: P
DeviceKey: ...\

Device Name: \
Device String: N
State Flags: 0
DeviceID: P
DeviceKey: ...\

Whereas it returned this:

Device Name: \\.\DISPLAY1
Device String: NVIDIA GeForce GTX 580
State Flags: 8000005
DeviceID: PCI\VEN_10DE&DEV_1080&SUBSYS_15803842&REV_A1
DeviceKey: ...\Control\Video\{B0CDD262-FCFB-4FD4-A03C-54621896C9CD}\0000

   Device Name: \\.\DISPLAY1\Monitor0
   Device String: Generic PnP Monitor
   State Flags: 3
   DeviceID: MONITOR\DEL4016\{4d36e96e-e325-11ce-bfc1-08002be10318}\0002
   DeviceKey: ...\Control\Class\{4d36e96e-e325-11ce-bfc1-08002be10318}\0002

Device Name: \\.\DISPLAY2
Device String: NVIDIA GeForce GTX 580
State Flags: 0
DeviceID: PCI\VEN_10DE&DEV_1080&SUBSYS_15803842&REV_A1
DeviceKey: ...\Control\Video\{B0CDD262-FCFB-4FD4-A03C-54621896C9CD}\0001

Device Name: \\.\DISPLAYV1
Device String: RDPDD Chained DD
State Flags: 8
DeviceID:
DeviceKey: ...\Control\Video\{DEB039CC-B704-4F53-B43E-9DD4432FA2E9}\0000

Device Name: \\.\DISPLAYV2
Device String: RDP Encoder Mirror Driver
State Flags: 200008
DeviceID:
DeviceKey: ...\Control\Video\{42cf9257-1d96-4c9d-87f3-0d8e74595f78}\0000

Device Name: \\.\DISPLAYV3
Device String: RDP Reflector Display Driver
State Flags: 200008
DeviceID:
DeviceKey: ...\Control\Video\{b043b95c-5670-4f10-b934-8ed0c8eb59a8}\0000

for the user who has provided this reference code

What is it that I am doing wrong here?

Upvotes: 2

Views: 743

Answers (1)

Miner_Glitch
Miner_Glitch

Reputation: 536

I suspect you have a problem with unicode.

It looks like your strings are only printing the first 8-bit char, because, in the strings you have, the chars are 16 bits and the next byte has a zero - so printf decides it is the end of the string.

Trying converting the strings from unicode to ascii before printing them.

Upvotes: 2

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