x86 MASM程序集-尽管FlushConsoleInputBuffer，输入缓冲区仍保留旧输入

Question

为了在MASM中练习组装，我创建了一个小程序，该程序应该执行以下操作：

1. 在屏幕上打印"键入a:">
2. 从输入缓冲区读取一个字符，然后对其进行刷新
3. 如果字符是"a"，则脱离循环并结束程序，否则，从第一步开始重复

我的代码如下：

.386

.model flat,stdcall

include masm32includekernel32.inc ; Defines Symbols To Be Used for the kernel32 library

includelib masm32libkernel32.lib

STD_OUTPUT_HANDLE equ -11
STD_INPUT_HANDLE equ -10
.code

entryPt proc
local inHandle:DWORD
local outHandle:DWORD
local noOfCharsWritten:DWORD
; Get Standard Output Handle
push STD_OUTPUT_HANDLE
call GetStdHandle
mov outHandle,eax
; Get Standard Input Handle
push STD_INPUT_HANDLE
call GetStdHandle
mov inHandle,eax
.while (eax == eax) ; while (true)
; Print "Type a: "
push 0
lea eax,noOfCharsWritten
push eax
push sizeof txt
push offset txt
push outHandle
call WriteConsoleA
; Poll for a byte
call getChar
.if (al == "a") ; if the byte was "a"...
.break ; ...then end the loop
.endif
.endw
; Leave with exit code 0
push 0
call ExitProcess
entryPt endp
getChar proc
local inHandle:DWORD
local noOfCharsRead:DWORD
local resBt:BYTE
; Get the Standard Input Handle
push STD_INPUT_HANDLE
call GetStdHandle
mov inHandle,eax
; Read one char from the console, put the result in resBt and the number of chars read in noOfCharsRead
push 0
lea eax,noOfCharsRead
push eax
push 1
lea eax,resBt
push eax
push inHandle
call ReadConsoleA
; Flush Console Input Buffer
push inHandle
call FlushConsoleInputBuffer
; Return the result in the accumulator
movzx eax,resBt
ret
getChar endp
.data
txt db "Type a: "
end entryPt

当键入"a"时，程序将退出，就像它应该退出一样。但是，如果我键入任何不是"a"(例如"s"(的内容，而不是再次查询"Typea:"，只查询一次，它将在查询另一个字节之前写入"Typea:Typea:Typea："。写多个非a字符会导致更多的"键入a:"s。

我怀疑这是因为ReadConsole正在读取旧的输入，因此提前终止了函数，但FlushConsoleInputBuffer不应该清除旧的输入吗？

Answer 1

ReadConsole从控制台输入缓冲区读取所有可用字符，并将它们存储在不受FlushConsoleInputBuffer影响的单独缓冲区中。您无法直接访问该缓冲区，也无法获取有关该缓冲区的信息。因此，您必须使用ReadConsole读取该缓冲区直到行尾。默认情况下，行的末尾标记有两个字节CR(0x0D(和LF(0x0A(。由于只读取一个字节，所以缓冲区中至少还剩下LF。

用ReadConsole循环替换FlushConsoleInputBuffer以清空缓冲区，直到读取LF：

.model flat,stdcall
include masm32includekernel32.inc ; Defines Symbols To Be Used for the kernel32 library
includelib masm32libkernel32.lib
STD_OUTPUT_HANDLE equ -11
STD_INPUT_HANDLE equ -10
.code
entryPt proc
local inHandle:DWORD
local outHandle:DWORD
local noOfCharsWritten:DWORD
; Get Standard Output Handle
push STD_OUTPUT_HANDLE
call GetStdHandle
mov outHandle,eax
; Get Standard Input Handle
push STD_INPUT_HANDLE
call GetStdHandle
mov inHandle,eax
.while (eax == eax) ; while (true)
; Print "Type a: "
push 0
lea eax,noOfCharsWritten
push eax
push sizeof txt
push offset txt
push outHandle
call WriteConsoleA
; Poll for a byte
call getChar
.if (al == "a") ; if the byte was "a"...
.break ; ...then end the loop
.endif
.endw
; Leave with exit code 0
push 0
call ExitProcess
entryPt endp
getChar proc
local inHandle:DWORD
local noOfCharsRead:DWORD
local resBt:BYTE, dummy:BYTE
; Get the Standard Input Handle
push STD_INPUT_HANDLE
call GetStdHandle
mov inHandle,eax
; Read one char from the console, put the result in resBt and the number of chars read in noOfCharsRead
push 0
lea eax,noOfCharsRead
push eax
push 1
lea eax,resBt
push eax
push inHandle
call ReadConsoleA
; Flush
mov al, resBt
mov dummy, al
FlushLoop:
cmp dummy, 0Ah
je EndOfFlush
invoke ReadConsoleA, inHandle, ADDR dummy, 1, ADDR noOfCharsRead, 0
jmp FlushLoop
EndOfFlush:
; Return the result in the accumulator
movzx eax,resBt
ret
getChar endp
.data
txt db "Type a: "
end entryPt