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\n", MessageBox("Done Title", "This test is Done.", MB_YESNOCANCEL))
}

func init() {
	fmt.Print("Starting Up\n")
}

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\n", 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.

AVX512 Articles AssemblyPolicy Benchmarks Blogs Books BoundingResourceUse CSSStyleGuide ChromeOS CodeReview CodeReviewComments CodeReviewConcurrency CodeTools Comments CommitMessage CommonMistakes CompilerOptimizations Conferences Configuring GoLand for WebAssembly Contributing to gopls CoreDumpDebugging Courses CreatingSubRepository CustomPprofProfiles Darwin DashboardBuilders Deprecated DesignDocuments Diagnostics Download build farm failed logs and debugging DragonFly BSD ErrorValueFAQ Errors ExperienceReports FileTreeDocumentation FreeBSD FromXToGo Frozen Fuzzing trophy case GOPATH Gardening GcToolchainTricks GccgoCrossCompilation GerritAccess GerritBot GithubAccess Go 1.10 Release Party Go 1.6 release party Go 1.8 Release Party Go Community Slides Go Release Cycle Go2 Go2ErrorHandlingFeedback Go2ErrorValuesFeedback Go2GenericsFeedback GoArm GoForCPPProgrammers GoGenerateTools GoGetProxyConfig GoGetTools GoMips GoStrings GoTalks GoUserGroups GoUsers Gomote Gopher HandlingIssues Home HostedContinuousIntegration How to ask for help HowToAsk IDEsAndTextEditorPlugins InstallFromSource InstallTroubleshooting InterfaceSlice InvalidFlag Iota Learn LearnConcurrency LearnErrorHandling LearnServerProgramming LearnTesting Linux LinuxKernelSignalVectorBug Livestreams LockOSThread MacOS12BSDThreadRegisterIssue MethodSets MinimumRequirements MinorReleases Mobile Modules MutexOrChannel NativeClient NetBSD NewSpeakers NoMeToo NoPlusOne NonEnglish OpenBSD PackagePublishing PanicAndRecover PerfDashboard Performance Plan9 Podcasts PortingPolicy PriorDiscussion Projects Proposals ProviderIntegration Questions Quiet Weeks Range RateLimiting ResearchPapers Resolving Problems From Modified Module Path Resources for slog SQLDrivers SQLInterface Screencasts SettingGOPATH SignalHandling SimultaneousAssignment SliceTricks SlowBots Solaris Spectre Spelling Style SuccessStories Switch TableDrivenTests TargetSpecific TestComments TestFailures Timeouts Training Ubuntu Watchflakes WebAccessibilityResourcesAndTips Well known struct tags WhyGo Windows WindowsBuild WindowsCrossCompiling WindowsDLLs X Repositories _Footer cgo golang tools gopherbot gopls integrator FAQ gopls heapdump13 heapdump14 heapdump15 through heapdump17 heapdump15