I got a problem with reading to a buffer using fgets in assemmbly. I know that the numbers are equal to the ASCII value ATM , and its not the problem. I cant get the real value of the user input. Before using fgets I am required to print the string: "calc:" and i think its messing with my real input.
section .rodata
CALC: DB "calc:" , 10 , 0 ;format string
section .bss
buffer: resb 80 ;store my input
;....more data, not relevant
push CALC ;push string to stuck
call printf
add esp, 4 ;remove pushed argument
push dword [stdin] ;fgets need 3 param
push dword 80 ;max lenght
push dword buffer ;input buffer
call fgets
add esp, 12 ;remove 3 push from stuck
mov ecx, [buffer] ;THIS IS FOR GDB
stop_here:
Now, the problem is that the value in buffer isn't what the user put in the input. when I used the GDB debugger for better understanding I got the following results:
input 0 --> ecx value is: 2608 (should be 48)
input 1 --> ecx value is: 2609 (should be 49)
input 10 --> ecx value is: 667697 (should be 48+49)
input 34 --> ecx value is: 668723 (should be 51+52)
EDIT: I tryed using gets instead, and now it works! can someone PLEASE explain to me why?!
EDIT- 5 years later - I can't believe I knew this much assembly back then
fgets stores the terminating line feed into the buffer as well, and since you are loading 4 bytes into ecx, you will also see that.
2608 = 0A30 hex = '0' LF
667697 = 0A3031 hex = '1' '0' LF
(Remember that x86 is little endian.)