Source name     : CHARSIN.ASM
;  Executable name : CHARSIN
;  Version         : 2.0
;  Created date    : 11/21/1999
;  Last update     : 5/28/2009
;  Author          : Jeff Duntemann
;  Description     : A character input demo for Linux, using NASM 2.05,
;                    incorporating calls to both fgets() and scanf().
;
;  Build using these commands:
;    nasm -f elf -g -F stabs charsin.asm
;    gcc charsin.o -o charsin
;

[SECTION .data]                ; Section containing initialised data

SPrompt  db 'Enter string data, followed by Enter: ',0
IPrompt  db 'Enter an integer value, followed by Enter: ',0
IFormat  db '%d',0
SShow    db 'The string you entered was: %s',10,0
IShow    db 'The integer value you entered was: %5d',10,0

[SECTION .bss]         ; Section containing uninitialized data

IntVal   resd 1        ; Reserve an uninitialized double word
InString resb 128m     ; Reserve 128 bytes for string entry buffer

[SECTION .text]        ; Section containing code

extern stdin           ; Standard file variable for input
extern fgets
extern printf
extern scanf
global main            ; Required so linker can find entry point

main:

push ebp        ; Set up stack frame for debugger
       mov ebp,esp
       push ebx        ; Program must preserve ebp, ebx, esi, & edi
       push esi
       push edi
;;; Everything before this is boilerplate; use it for all ordinary apps!

; First, an example of safely limited string input using fgets:
       push Sprompt    ; Push address of the prompt string
       call printf     ; Display it
       add esp,4       ; Stack cleanup for 1 parm

       push dword [stdin]  ; Push file handle for standard input
       push 72         ; Accept no more than 72 chars from keybd
       push InString   ; Push address of buffer for entered chars
       call fgets      ; Call fgets
       add esp,12      ; Stack cleanup: 3 parms X 4 bytes = 12

       push InString   ; Push address of entered string data buffer
       push Sshow      ; Push address of the string display prompt
       call printf     ; Display it
       add esp,8       ; Stack cleanup: 2 parms X 4 bytes = 8

; Next, use scanf() to enter numeric data:
       push Iprompt    ; Push address of the integer input prompt
       call printf     ; Display it
       add esp,4       ; Stack cleanup for 1 parm

       push IntVal     ; Push the address of the integer buffer
       push Iformat    ; Push the address of the integer format string
       call scanf      ; Call scanf to enter numeric data
       add esp,8       ; Stack cleanup: 2 parms X 4 bytes = 8

       push dword [IntVal]  ; Push integer value to display
       push Ishow      ; Push base string
       call printf     ; Call printf to convert & display the integer
       add esp,8       ; Stack cleanup: 2 parms X 4 bytes = 8

;;; Everything after this is boilerplate; use it for all ordinary apps!
       pop edi         ; Restore saved registers
       pop esi
       pop ebx
       mov esp,ebp     ; Destroy stack frame before returning
       pop ebp
       ret             ; Return control to Linux

[SECTION .data]        ; Section containing initialised data

sprompt  db 'Enter string data, followed by Enter: ',0
iprompt  db 'Enter an integer value, followed by Enter: ',0
iformat  db '%d',0
sshow    db 'The string you entered was: %s',10,0
ishow    db 'The integer value you entered was: %5d',10,0

[SECTION .bss]         ; Section containing uninitialized data

intval   resd 1        ; Reserve an uninitialized double word
instring resb 128      ; Reserve 128 bytes for string entry buffer