How to iterate over individual characters of a string in x86 assembly and print them?
global _main ; declare _main entry point
extern _printf ; extern method
section .data
string: db 'Iterate over this string #test', 0
character: db '_', 0
endStr: db 'Ended.', 0
section .text
_main:
lea eax, string ;load address of string to eax
loop:
mov cl, [eax] ; access [eax] in memory, save char to cl
test cl, cl ; check if zero terminator
jz end ; exit if 0
mov [character], cl ; write char to memory (character)
push character ; print character
call _printf
add esp, 4 ; clear stack
inc eax ; increment address
jmp loop ; loop again
end:
ret ; exit
My current program crashes after printing the first character of the string, "I". There is no error outputted to the console.
Thanks for any help in advance.
eax is not a call-preserved register. After the call to printf, eax is garbage.
The immediate best solution is to use register esi instead.
I'm actually in a little bit of trouble here because of the 16 byte stack alignment required for modern glibc, and I don't know the calling convention rules well enough to preserve it. But that doesn't seem to be why you are crashing.