Flat assembler: reading files, using fopen+fread

FILE.ASM

 format PE GUI 3.1

 use16
 align 1
 entry start
 heap 0
 stack 0

 include 'win32a.inc'

 struct _iobuf
    _ptr      dd ? ; char*
    _cnt      dd ? ; int
    _base     dd ? ; char*
    _flag     dd ? ; int
    _file     dd ? ; int
    _charbuf  dd ? ; int
    _bufsiz   dd ? ; int
    _tmpfname dd ? ; char*
 ends

 section '' code data readable executable writeable shareable discardable notpageable
   start:
     invoke fopen,c,d
     mov    [a],eax
     invoke fread,b,1,16,[a]
     invoke MessageBox,HWND_DESKTOP,b,c,MB_OK
     invoke fclose,[a]
     invoke ExitProcess,0

   a _iobuf ?
   b db 17 dup ?
   c db 'FILE.TXT',0
   d db 'r',0

 section '' import data readable writeable
   library kernel,'KERNEL32.DLL',\
           msvcrt,'msvcrt.dll',\
           user32,'USER32.DLL'
   import kernel,\
          ExitProcess,'ExitProcess'
   import msvcrt,\
          fopen,'fopen',\
          fread,'fread'
   import user32,\
          MessageBox,'MessageBoxA'

msvcrt blooooaaattt use createfile