Question

Using Windows API perform following exercise:

Implement your own version of the ReadString procedure, using stack parameters. Pass it a
pointer to a string and an integer, indicating the maximum number of characters to be entered.
Return a count (in EAX) of the number of characters actually entered. The procedure must input
a string from the console and insert a null byte at the end of the string (in the position occupied

by 0Dh). See Section 11.1.4 for details on the Win32 ReadConsole function. Write a short pro-
gram that tests your procedure.

Assembly please thanks!

Answer 1

Read_String PROTO,
   bufferPtr:PTR DWORD,
   bufferSize:DWORD,

BufSize = 80

.data
buffer BYTE BufSize DUP(?)
msg BYTE "Please enter a string: "

.code
main PROC

; Display a prompt
   mov edx, OFFSET msg   ; message to display
   call WriteString

; Input a string
   INVOKE Read_String,
   ADDR buffer,   ; points to buffer
   BufSize   ; size of buffer

; EAX now contains the number of bytes entered
   call DumpRegs

; Display the buffer
   mov edx,OFFSET buffer
   call WriteString
   call Crlf

;   mov esi, OFFSET buffer
;   mov ecx, eax   ; number of characters read
;   mov ebx, TYPE buffer    ; one character per byte
;   call DumpMem

   exit
main ENDP

;-------------------------------------------------------
Read_String PROC USES esi,
   bufferPtr:PTR DWORD,
   bufferSize:DWORD
LOCAL stdInHandle:DWORD, bytesRead:DWORD
;
; Wrapper procedure for the function ReadConsole in the
; Windows API. The user enters a string which is stored
; in the buffer pointed to by the bufferPtr parameter.
; Receives: bufferPtr and bufferSize
; Returns: EAX = number of characters actually entered
;-------------------------------------------------------
;.data
;stdInHandle DWORD ?
;bytesRead DWORD ?
;.code
   ; Get handle to standard input
   INVOKE GetStdHandle, STD_INPUT_HANDLE
   mov stdInHandle, eax   ; save standard input handle

   ; Get user input
   INVOKE ReadConsole, stdInHandle, bufferPtr,
   bufferSize, ADDR bytesRead, 0

   sub bytesRead,2
   mov esi, bufferPtr   ; ESI = pointer to buffer
   add esi, bytesRead   ; ESI = end of buffer
;   sub esi, 2   ; ESI = position of 0Dh
;   mov al, 0   ; AL = null
   mov BYTE PTR[esi], 0   ; replace 0Dh with null

   mov eax, bytesRead   ; EAX = characters read

   ret
Read_String ENDP

END main