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+---- Thread: [Assembly] Intel x86 NASM Using fgets (/showthread.php?tid=4860009)
Intel x86 NASM Using fgets - splutter - Jun 11, 2015
So I have a piece of code and I'm attempting to scan in a string with a call to fgets. It's not reading anything in and the return value is NULL. May someone tell me how I could check my error value or teach me how I should approach this?
My code goes something like this:
Code
...
push DWORD 0x0 ; STDIN is 0
push BYTE 0xA ; Max size is 10
push DWORD buf ; load address of buffer for input
call _fgets
add esp 0xC ; reset stack pointer
cmp eax, 0x0 ; check return value in eax
jz err ; jump to error address if NULL
...* - Only3 - Jun 11, 2015
char fgets ( char str, int num, FILE * stream ); http://www.cplusplus.com/reference/cstdio/fgets
push stream
push num
push str
call fgets
* - Mr. Dr. Prof. Patrick - Jun 11, 2015
STDIN is not 0, STDIN is a maco and there is a function you can use to find the address of STDIN
Code
push eax
call ___iob_func ; returns an array containing addresses of Files like stdio, stdout
push eax ; STDIN is the first in the array that is returned giving it postion 0
push BYTE 0xA ; Max size is 10
push DWORD buf ; load address of buffer for input
call _fgets* - Masm4ever - Jun 12, 2015
Shorter (but you need a modern assembler):
invoke crt_fgets, addr buffer, sizeof buffer, rv(crt___p__iob)