msvcrt.dll, getting one symbol from console hint

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twgt

Joined: 23 Jan 2007
Posts: 8

twgt 03 Jan 2008, 04:27

Some days ago, I tried to use function scanf from msvcrt.dll library for taking one char from console.
Every second attempt call function return value without asking user.

Code:

 cinvoke scanf,"%c",userinput

I print 'y'

Code:

 cinvoke scanf,"%c",userinput1

After this manipulation userinput contain 'y', but userinput1 contain 0x0A

in C language it can be viewed by next code

Code:

  unsigned int x, m;      
     scanf("%c",&x );     //x="y"
     scanf("%c",&m);     //m=0x0A
     scanf("%c",&m);     //m="y"

for correct using of this method of taking input char use "%s" as argument for scanf-function.

PS. functions getchar() and getc() also not returning char when they called twice
PPS. Thanks Stiver!

03 Jan 2008, 04:27

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20526
Location: In your JS exploiting you and your system

revolution 03 Jan 2008, 06:36

twgt: I am not sure what you are saying. Is that a question or are you offering advice?

03 Jan 2008, 06:36

twgt

Joined: 23 Jan 2007
Posts: 8

twgt 03 Jan 2008, 07:24

revolution, it's experience. Smile

Look at real sample.

Code:

.loop:                   ;wait for connect
        ..............................................................
        cinvoke printf,<"Accept connection?[y/n]: ">
        mov dword[userinput],0
        cinvoke scanf,"%c",userinput
        cinvoke printf,<13,10>
        cmp [userinput],'y'
        jz @accept_connection
        cinvoke printf,<"Connection not accepted",13,10,"Wait for another connection",13,10>
        invoke closesocket,[clientsock]
        ;mov [clientsock],0
        jmp .loop

Log of work:

Quote:

Accept connection?[y/n]: n

Connection not accepted
Wait for another connection

Accept connection?[y/n]:

Connection not accepted
Wait for another connection

Accept connection?[y/n]: n

Connection not accepted
Wait for another connection

Accept connection?[y/n]:

Connection not accepted
Wait for another connection

Understand?

03 Jan 2008, 07:24

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20526
Location: In your JS exploiting you and your system

revolution 03 Jan 2008, 07:44

You might want to think about draining the keyboard buffer before asking the user for input. But it depends on how your program operates as to whether that is a good alternative.

03 Jan 2008, 07:44

Yardman

Joined: 12 Apr 2005
Posts: 244
Location: US

Yardman 03 Jan 2008, 08:01

[ Post removed by author. ]

Last edited by Yardman on 04 Apr 2012, 03:08; edited 1 time in total

03 Jan 2008, 08:01

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 03 Jan 2008, 09:46

twgt: "scanf("%c", ...)" is NOT waiting for user to type one character. It is reading one character from STDIN. Stdin can be redirected from file, in that case user doesn't type anything.

If stdin is not redirected from file, it reads from console. Any reading from console causes program to stop, and lets user type one line, regardless of how much you are reading from it. After you type one line, desired amount of characters are returned, and rest stay buffered, and are returned in sebsequent reads.

For example, in your demo, try to type "abcdyynnyn" and then hit tner.

03 Jan 2008, 09:46

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