WindowsDLLs
Gopal Adhikari edited this page on Apr 29, 2018 · 6 revisions
Calling a Windows DLL
Go allows you to call native Windows function in several different ways.
Dynamically load a DLL, then call a function in it. You can call the function via SyscallX (where X is the number of parameters. If the function has fewer parameters than that, for example passing 7 arguments to a function that accepts 9, Syscall9 will still work, you just need to specify 7 as your second argument to Syscall9).
A sample Go program that calls a Windows DLL function using this method:
package main
import (
"fmt"
"syscall"
"unsafe"
)
func abort(funcname string, err error) {
panic(fmt.Sprintf("%s failed: %v", funcname, err))
}
var (
kernel32, _ = syscall.LoadLibrary("kernel32.dll")
getModuleHandle, _ = syscall.GetProcAddress(kernel32, "GetModuleHandleW")
user32, _ = syscall.LoadLibrary("user32.dll")
messageBox, _ = syscall.GetProcAddress(user32, "MessageBoxW")
)
const (
MB_OK = 0x00000000
MB_OKCANCEL = 0x00000001
MB_ABORTRETRYIGNORE = 0x00000002
MB_YESNOCANCEL = 0x00000003
MB_YESNO = 0x00000004
MB_RETRYCANCEL = 0x00000005
MB_CANCELTRYCONTINUE = 0x00000006
MB_ICONHAND = 0x00000010
MB_ICONQUESTION = 0x00000020
MB_ICONEXCLAMATION = 0x00000030
MB_ICONASTERISK = 0x00000040
MB_USERICON = 0x00000080
MB_ICONWARNING = MB_ICONEXCLAMATION
MB_ICONERROR = MB_ICONHAND
MB_ICONINFORMATION = MB_ICONASTERISK
MB_ICONSTOP = MB_ICONHAND
MB_DEFBUTTON1 = 0x00000000
MB_DEFBUTTON2 = 0x00000100
MB_DEFBUTTON3 = 0x00000200
MB_DEFBUTTON4 = 0x00000300
)
func MessageBox(caption, text string, style uintptr) (result int) {
var nargs uintptr = 4
ret, _, callErr := syscall.Syscall9(uintptr(messageBox),
nargs,
0,
uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(text))),
uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(caption))),
style,
0,
0,
0,
0,
0)
if callErr != 0 {
abort("Call MessageBox", callErr)
}
result = int(ret)
return
}
func GetModuleHandle() (handle uintptr) {
var nargs uintptr = 0
if ret, _, callErr := syscall.Syscall(uintptr(getModuleHandle), nargs, 0, 0, 0); callErr != 0 {
abort("Call GetModuleHandle", callErr)
} else {
handle = ret
}
return
}
func main() {
defer syscall.FreeLibrary(kernel32)
defer syscall.FreeLibrary(user32)
fmt.Printf("Return: %d
", MessageBox("Done Title", "This test is Done.", MB_YESNOCANCEL))
}
func init() {
fmt.Print("Starting Up
")
}
Using syscall.NewProc instead of syscall.GetProcAddress. These are basically some helper methods over the syscall ones, you saw above, and are available in Windows only: http://golang.org/src/pkg/syscall/dll_windows.go
package main
import (
"fmt"
"syscall"
"unsafe"
)
func main() {
var mod = syscall.NewLazyDLL("user32.dll")
var proc = mod.NewProc("MessageBoxW")
var MB_YESNOCANCEL = 0x00000003
ret, _, _ := proc.Call(0,
uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr("This test is Done."))),
uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr("Done Title"))),
uintptr(MB_YESNOCANCEL))
fmt.Printf("Return: %d
", ret)
}
By "linking" against the library, using the "cgo" method (this way works in Linux and Windows). Example:
import ("C")
...
C.MessageBoxW(...)
See cgo for further details.