Call windows function (getting the font directory)

For example,

package main

import (
    "fmt"
    "syscall"
    "unsafe"
)

type GUID struct {
    Data1 uint32
    Data2 uint16
    Data3 uint16
    Data4 [8]byte
}

var (
    FOLDERID_Fonts = GUID{0xFD228CB7, 0xAE11, 0x4AE3, [8]byte{0x86, 0x4C, 0x16, 0xF3, 0x91, 0x0A, 0xB8, 0xFE}}
)

var (
    modShell32               = syscall.NewLazyDLL("Shell32.dll")
    modOle32                 = syscall.NewLazyDLL("Ole32.dll")
    procSHGetKnownFolderPath = modShell32.NewProc("SHGetKnownFolderPath")
    procCoTaskMemFree        = modOle32.NewProc("CoTaskMemFree")
)

func SHGetKnownFolderPath(rfid *GUID, dwFlags uint32, hToken syscall.Handle, pszPath *uintptr) (retval error) {
    r0, _, _ := syscall.Syscall6(procSHGetKnownFolderPath.Addr(), 4, uintptr(unsafe.Pointer(rfid)), uintptr(dwFlags), uintptr(hToken), uintptr(unsafe.Pointer(pszPath)), 0, 0)
    if r0 != 0 {
        retval = syscall.Errno(r0)
    }
    return
}

func CoTaskMemFree(pv uintptr) {
    syscall.Syscall(procCoTaskMemFree.Addr(), 1, uintptr(pv), 0, 0)
    return
}

func FontFolder() (string, error) {
    var path uintptr
    err := SHGetKnownFolderPath(&FOLDERID_Fonts, 0, 0, &path)
    if err != nil {
        return "", err
    }
    defer CoTaskMemFree(path)
    folder := syscall.UTF16ToString((*[1 << 16]uint16)(unsafe.Pointer(path))[:])
    return folder, nil
}

func main() {
    folder, err := FontFolder()
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println("Font Folder:", folder)
}

Output:

Font Folder: C:\Windows\Fonts

Just in case someone needs the folder id for documents in golang format:

Replace this in peterSO's code example:

FOLDERID_Documents = GUID{0xFDD39AD0, 0x238F, 0x46AF, [8]byte{0xAD, 0xB4, 0x6C, 0x85, 0x48, 0x03, 0x69, 0xC7}}

FOLDERID_PublicDocuments = GUID{0xED4824AF, 0xDCE4, 0x45A8, [8]byte{0x81, 0xE2, 0xFC, 0x79, 0x65, 0x08, 0x36, 0x34}}

see

https://msdn.microsoft.com/en-us/library/windows/desktop/dd378457(v=vs.85).aspx