用lxn / win处理golang中的LPTSTR

Question

I have this piece of code which runs without returning err but simply doesn't do its job because it doesn't return the expected value. The idea is to use SHGetSpecialFolderPath in order to retrieve the path to the Windows directory (C:\Windows for example). This api call has the following signature:

BOOL SHGetSpecialFolderPath(
        HWND   hwndOwner, 
        _Out_ LPTSTR lpszPath,
        _In_  int    csidl,
        _In_  BOOL   fCreate );

I know it is deprecated, but still available even on current Windows versions. I have to use this API because I need to support Windows versions older than Windows 7 (I know that these are old or even end of life)

This is the piece of code:

target := "XXX...XXX" // hard coded string with more than 600 characters
buffer, err := syscall.UTF16PtrFromString(target)
if err != nil {
        fmt.Println("conversion of string:", err)
}

result := win.SHGetSpecialFolderPath(0, buffer, win.CSIDL_WINDOWS, false)
if err != nil {
    fmt.Println("result of get folder:", err)
}

fmt.Println("folder retrieved ok: ", result)
fmt.Println("folder: ", target)
}

None of the err is set, the API call returns true but the string is unchanged:

folder retrieved ok:  true
folder: XXX...XXX

The result is the same on Windows 10 x64 and on my testing VM running Windows XP SP3 (I know that XP is inherently unsafe)

I have seen examples how to use LPTRSTR with unsafe and uintptr here on SO and other sites but none of them compile on my version of golang (which is go version go1.10.1 windows/amd64, I compiled with GOARCH=386)

Answer 1

Approach the problem in a logical, systematic fashion.

---

Carefully read the Microsoft documentation for the function.

SHGetSpecialFolderPath function

---

Carefully read the lxn/win package documentation for the function.

package win

import "github.com/lxn/win" 

func SHGetSpecialFolderPath

func SHGetSpecialFolderPath(hwndOwner HWND, lpszPath *uint16, csidl CSIDL, fCreate bool) bool

---

Now, using the documentation, implement the function call in Go. Go Unicode strings are UTF-8 encoded. Windows Unicode strings are UTF-16 encoded.

package main

import (
    "fmt"
    "syscall"

    "github.com/lxn/win"
)

func main() {
    buf := make([]uint16, win.MAX_PATH)
    rv := win.SHGetSpecialFolderPath(win.HWND(0), &buf[0], win.CSIDL_WINDOWS, false)
    fmt.Println(rv)
    path := syscall.UTF16ToString(buf)
    fmt.Println(path)
}

Output:

true
C:\Windows