Golang下通过syscall调用win32的dll（calling Windows DLLs from Go ）
很多同学比如我虽然很喜欢golang，但是还是需要调用很多遗留项目或者其他优秀的开源项目，这时怎么办呢？我们想到的方法是用package里的syscall结合cgo
注意此处有坑：
在我调试时显示not enough arguments in call to syscall.Syscall
[ `go run dms.go` | done: 260.3744ms ]
# command-line-arguments
.\dms.go:72: not enough arguments in call to syscall.Syscall
exit status 2
因为我参照的是http://golang.org/pkg/syscall/#Syscall ，而其默认的是Linux/Unix的syscall API doc说明，
如何看windows的golang doc呢？
通过godoc command, 调用 godoc -http=:6060
然后在浏览器打开http://localhost:6060/pkg/syscall/#Syscall，这才是windows的golang pakage api
func Syscall
func Syscall(trap, nargs, a1, a2, a3 uintptr) (r1, r2 uintptr, err Errno)
Implemented in ../runtime/syscall_windows.goc.
func Syscall12
func Syscall12(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12 uintptr) (r1, r2 uintptr, err Errno)
func Syscall15
func Syscall15(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15 uintptr) (r1, r2 uintptr, err Errno)
func Syscall6
func Syscall6(trap, nargs, a1, a2, a3, a4, a5, a6 uintptr) (r1, r2 uintptr, err Errno)
func Syscall9
func Syscall9(trap, nargs, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err Errno)
例子1：
func test(){
//首先,准备输入参数, GetDiskFreeSpaceEx需要4个参数, 可查MSDN
lpFreeBytesAvailable := int64(0) //注意类型需要跟API的类型相符
lpTotalNumberOfBytes := int64(0)
lpTotalNumberOfFreeBytes := int64(0)
//获取方法的引用
kernel32, _ := syscall.LoadLibrary("Kernel32.dll") // 严格来说需要加上 defer syscall.FreeLibrary(kernel32)
GetDiskFreeSpaceEx, _ := syscall.GetProcAddress(syscall.Handle(kernel32), "GetDiskFreeSpaceExW")
//执行之. 因为有4个参数,故取Syscall6才能放得下. 最后2个参数,自然就是0了
r, _, _ := syscall.Syscall6(uintptr(GetDiskFreeSpaceEx), 4,
uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr("C:"))),
uintptr(unsafe.Pointer(&lpFreeBytesAvailable)),
uintptr(unsafe.Pointer(&lpTotalNumberOfBytes)),
uintptr(unsafe.Pointer(&lpTotalNumberOfFreeBytes)), 0, 0)
// 注意, errno并非error接口的, 不可能是nil
// 而且,根据MSDN的说明,返回值为0就fail, 不为0就是成功
if r != 0 {
log.Printf("Free %dmb", lpTotalNumberOfFreeBytes/1024/1024)
}
}
例子2，弹出一个简单的对话框messagebox， http://code.google.com/p/go-wiki/wiki/WindowsDLLs：
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")}
http://golang.org/pkg/syscall/#Syscall 里默认的是Linux/Unix的syscall API doc说明，