In this guide, we will discuss CMPS Instruction in Assembly Programming Language. The CMPS instruction compares two strings. This instruction compares two data items of one byte, word or doubleword, pointed to by the DS:SI and ES:DI registers and sets the flags accordingly. You can also use the conditional jump instructions along with this instruction.
The following example demonstrates comparing two strings using the CMPS instruction −
section .text global _start ;must be declared for using gcc _start: ;tell linker entry point mov esi, s1 mov edi, s2 mov ecx, lens2 cld repe cmpsb jecxz equal ;jump when ecx is zero ;If not equal then the following code mov eax, 4 mov ebx, 1 mov ecx, msg_neq mov edx, len_neq int 80h jmp exit equal: mov eax, 4 mov ebx, 1 mov ecx, msg_eq mov edx, len_eq int 80h exit: mov eax, 1 mov ebx, 0 int 80h section .data s1 db 'Hello, world!',0 ;our first string lens1 equ $-s1 s2 db 'Hello, there!', 0 ;our second string lens2 equ $-s2 msg_eq db 'Strings are equal!', 0xa len_eq equ $-msg_eq msg_neq db 'Strings are not equal!' len_neq equ $-msg_neq
When the above code is compiled and executed, it produces the following result −
Strings are not equal!
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