In this tutorial, we'll look at how to create a directory.
Overview
- Directory Handling
- CreateDirectory Windows Function
- Example Program
Directory Handling
In the next few tutorials, we'll make programs that would do some basic things in managing directories. In this tutorial, we would make a new directory, if one does not already exist, and display an okay message; otherwise, if the directory already exists, we would display a message box with an error message.
The third parameter of the MessageBox() function is the title for the message box; if that parameter is NULL, a default value of "Error" is used.
Besides this, in the next few tutorials, we would go over handling every item in a directory, changing the current directory, removing a directory, and deleting a file.
So first of all, to make a directory, we would need to use the CreateDirectory() Win32 API function; let's take a look at that.
CreateDirectory Windows Function
The CreateDirectory() Win32 API function makes a directory at the path specified by the first parameter. All the intermediate directories in the path have to already exist, by the time you call this function.
Parameters:
- The path to the new directory.
- An optional pointer to a SECURITY_ATTRIBUTES structure.
Return:
BOOL
If the function succeeds, the return value is non-zero (TRUE).
The return value is zero (FALSE), otherwise.
This function has ANSI and Unicode versions (CreateDirectoryA and CreateDirectoryW; just CreateDirectory won't work).
We would be using the CreateDirectoryA() version of the function.
This function is part of the kernel32.dll DLL. The kernel32.dll DLL contains a lot of the functions that are needed for a program to survive (ie memory allocation, file I/O, etc.).
For more reference to this function, go to CreateDirectory Function (Windows).
Example Program
Okay, now let's use the CreateDirectory() function.
The Plan
Use the CreateDirectoryA() Win32 API function to make a new directory, named our_dir.
If successful, display a message box that says so; display an error message box, otherwise.
To display a success message, we would need to compile a string from parts. We would need to copy part 1 of the message to a string, then append the name of the directory to that string, and then append part 2 of the message to the string.
Similar with the error message, except that we use part 1 and part 2 of the error message, for the copying and appending, instead of using the regular message's part 1 and part 2.
The Code
;; Define the externs. extern CreateDirectoryA extern MessageBoxA extern ExitProcess ;; Construct our symbol import table. import CreateDirectoryA kernel32.dll import MessageBoxA user32.dll import ExitProcess kernel32.dll ;; The following goes into the code section; use 32-bit code. section .text use32 ;; Start program execution here. ..start: ;; Call the main() function. call main ;; Exit, returning whatever main() returned. push eax call [ExitProcess] main: enter 0, 0 push dword 0 ;; The second argument is an optional pointer to a SECURITY_ATTRIBUTES structure. ;; Just as with the CreateFile(), the second parameter is optional, and can be NULL. push dword directory_name ;; The first argument is the pointer to a string that contains the name of the new directory. ;; This string doesn't have to be a plain name, it can also be a path to the new directory to make, but ;; if it's a path, all the parent directories of the new directory have to already exist by the time we ;; call this function. call [CreateDirectoryA] ;; And we call the function. cmp eax, 0 ;; CreateDirectoryA() returns 0 if it fails. jz .error ;; Set string1 to part1. push dword part1 push dword string1 call strcpy ;; Append directory_name to string1. push dword directory_name push dword string1 call strcat ;; Append part2 to string1. push dword part2 push dword string1 call strcat ;; Display a message box with the prepared message. push dword 0 push dword the_title push dword string1 push dword 0 call [MessageBoxA] ;; Clear the return value and go to .finish xor eax, eax jmp .finish .error: ;; Set string1 to err_p1 push dword err_p1 push dword string1 call strcpy ;; Append directory_name to string1 push dword directory_name push dword string1 call strcat ;; Append err_p2 to string1 push dword err_p2 push dword string1 call strcat ;; Display a message box with the prepared message. push dword 0 push dword 0 ;; If this parameter is NULL, MessageBoxA uses "Error" as a title. push dword string1 push dword 0 call [MessageBoxA] ;; Load the return value with 1 and go to .finish mov eax, 1 jmp .finish ;; There's no point of the 'jmp .finish' instruction, since it would go to .finish anyway (because .finish is ;; the label for the next instruction), but I put it there just for fun; the other reason I put it there is ;; in case I add another label between here and .finish, it would still go to .finish; it's kind of like ;; using a 'break' keyword, in JavaScript/C/C++/etc., at the end of a switch statement. .finish: leave ret %include "../inc/str.asm" ;; In order to use the string functions (strcpy, strcat, etc.), we need to ;; include the file that defines them. ;; The following goes into the data section. section .data ;; We define the string with the name of the directory we want to make. directory_name db "our_dir", 0 ;; The title for our message box. the_title db "Success!", 0 ;; And parts of the message we'll display in the message box. part1 db "The directory ", 0 part2 db " has been successfully made. ", 0 ;; Well, we might need an error message, in case CreateDirectoryA() fails. err_p1 db "Error. Could not make the directory ", 0 err_p2 db " . ", 0 ;; The following is for the bss section. section .bss ;; string1 is a blank string, to start out with. string1 resb 512
The Output
If the directory does not already exist, the output should be something like this:
(Fullsize Screenshot)
If the directory does exist, an error message should come up. You can remove the directory and try again, in that case.
References:
CreateDirectory Function (Windows)
First Tutorial:
Intro To Win32 Assembly, Using NASM
Previous Tutorial:
More About Arrays
Next Tutorial:
Directory Handling - Directory Listing
