SendInput无法模拟Print Screen按键的技术咨询

Print Screen is a tricky one— I’ve run into this exact issue before when working with full-screen apps and DirectInput-based software like emulators. The problem boils down to two key quirks of how Windows handles this specific key, and how you’re structuring your SendInput calls.

Here’s why your current code isn’t working: #

• System-level priority for Print Screen: Windows natively intercepts the Print Screen key to handle its built-in screenshot functionality. When you simulate the key via SendInput, this system-level capture might block the event from reaching your target app, especially if it’s running in full-screen mode or using DirectInput (which often bypasses the standard Windows message queue).
• Missing extended key flag: Print Screen is classified as an extended key in Windows, which means your SendInput calls need to include the KEYEVENTF_EXTENDEDKEY flag alongside the scan code. Your current code omits this flag, so the system doesn’t recognize the simulated key press as a valid Print Screen event.

Fixed code to simulate Print Screen correctly: #

#include "stdafx.h" //For create process & keyboard codes
#include <windows.h>
#include <stdio.h>
#include <tchar.h>

int main() {
 INPUT ip = {};
 ip.type = INPUT_KEYBOARD;
 ip.ki.wScan = 0;
 ip.ki.wVk = 0;
 ip.ki.dwExtraInfo = 0;
 ip.ki.dwFlags = 0;

 printf("Press a key, then taskswitch.\n");
 system("pause");
 Sleep(2000);

 // KEY DOWN: Print Screen with extended key flag
 ip.ki.wScan = 0x37; // Print Screen's hardware scan code
 ip.ki.dwFlags = KEYEVENTF_SCANCODE | KEYEVENTF_EXTENDEDKEY;
 SendInput(1, &ip, sizeof(INPUT));

 // Small delay to ensure the key-down event is processed
 Sleep(50);

 // KEY UP: Print Screen with extended key + key-up flags
 ip.ki.wScan = 0x37;
 ip.ki.dwFlags = KEYEVENTF_SCANCODE | KEYEVENTF_EXTENDEDKEY | KEYEVENTF_KEYUP;
 SendInput(1, &ip, sizeof(INPUT));

 printf("Done.\n");
 system("pause");
 return 0;
}

Key changes made: #

1. Added KEYEVENTF_EXTENDEDKEY to both the key-down and key-up events— this tells Windows you’re simulating an extended key like Print Screen.
2. Added a short Sleep(50) between the press and release events. This prevents Windows from merging the two events into an invalid "press-and-release-too-fast" action.

Additional notes for your emulator use case: #

• Run your frontend as admin: Full-screen emulators often run with elevated privileges, so your frontend might need admin rights to send input events to them.
• Check for emulator APIs: If SendInput still doesn’t work with FS-UAE, look into whether the emulator provides a native API or command-line arguments to trigger screenshots. This is often a more reliable approach than simulating hardware keys for DirectInput apps.

内容的提问来源于stack exchange，提问作者Domarius