nasm astrlwr_s函数 x86

xxx.asm

%define p1 ebp+8
%define p2 ebp+12
%define p3 ebp+16

section .text
  global dllmain
  export astrlwr_s

dllmain:
  mov eax,1
  ret 12

;-----------------------------------------;
;  将字符串转换为小写
;-----------------------------------------;
astrlwr_s:
  push ebp
  mov ebp,esp
  
  mov eax,[p1]	; str ptr
  mov ecx,[p2]	; numberOfElements
  
  .for:
  
  test ecx,ecx
  jz .return
  
  mov dl,[eax]
  test dl,dl
  jz .return
  
  ;----------------------------------------;
  ; 如果 < 0x41 next
  ;----------------------------------------;
  cmp dl,41h
  jb .next

  ;----------------------------------------;
  ; 如果 > 0x5A next
  ;----------------------------------------;
  cmp dl,5Ah
  ja .next
  
  add dl,20h
  mov [eax],dl
  
  .next:
  dec ecx
  inc eax
  jmp .for
  
  .return:
  xor eax,eax
  mov esp,ebp
  pop ebp
  ret 8

c++:

#include <iostream>
#include <Windows.h>

typedef int (CALLBACK* astrlwr_s_t)(char* str, size_t numberOfElements);

astrlwr_s_t astrlwr_s;

int main()
{
  HMODULE myDLL = LoadLibraryA("xxx.dll");
  astrlwr_s = (astrlwr_s_t)GetProcAddress(myDLL, "astrlwr_s");

  char a[10] = "aBcD";
  printf("%d, %s
", _strlwr_s(a, 10), a); // abcd


  char b[10] = "aBcD";
  printf("%d, %s
", astrlwr_s(b, 10), b); // abcd
  return 0;
}