Golang中VB6调用DLL出现"Bad DLL calling convention"错误的解决方案

问题在于VB6默认使用stdcall调用约定，而Go默认导出的是cdecl调用约定。你需要使用//go:export指令配合syscall调用约定来导出函数。

以下是修正后的Go代码：

package main

// +build windows win32

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

//export GetIntFromDLL
func GetIntFromDLL() int32 {
	return 42
}

//export PrintHello
func PrintHello(Name *C.char, Output **C.char) int32 {
	*Output = C.CString(fmt.Sprintf("From DLL: Hello, %s!", C.GoString(Name)))
	return int32(len(C.GoString(*Output)))
}

//export PrintBye
func PrintBye(Output **C.char) int32 {
	*Output = C.CString(fmt.Sprintf("From DLL: Bye!"))
	return int32(len(C.GoString(*Output)))
}

//export LenString
func LenString(Input *C.char) int32 {
	return int32(len(C.GoString(Input)))
}

//export OutString
func OutString() (Output *C.char) {
	buf := C.CString("I am out string from DLL")
	return buf
}

func main() {
	// main
}

// 使用syscall.Syscall来确保stdcall调用约定
var (
	mod = syscall.NewLazyDLL("testDLL.dll")
	procGetIntFromDLL = mod.NewProc("GetIntFromDLL")
	procPrintHello = mod.NewProc("PrintHello")
	procPrintBye = mod.NewProc("PrintBye")
	procLenString = mod.NewProc("LenString")
	procOutString = mod.NewProc("OutString")
)

// 包装函数确保stdcall
func GetIntFromDLLWrapper() int32 {
	ret, _, _ := procGetIntFromDLL.Call()
	return int32(ret)
}

func PrintHelloWrapper(Name *C.char, Output **C.char) int32 {
	ret, _, _ := procPrintHello.Call(uintptr(unsafe.Pointer(Name)), uintptr(unsafe.Pointer(Output)))
	return int32(ret)
}

func PrintByeWrapper(Output **C.char) int32 {
	ret, _, _ := procPrintBye.Call(uintptr(unsafe.Pointer(Output)))
	return int32(ret)
}

func LenStringWrapper(Input *C.char) int32 {
	ret, _, _ := procLenString.Call(uintptr(unsafe.Pointer(Input)))
	return int32(ret)
}

func OutStringWrapper() *C.char {
	ret, _, _ := procOutString.Call()
	return (*C.char)(unsafe.Pointer(ret))
}

编译命令需要添加-ldflags "-s -w -H=windowsgui"来确保正确的调用约定：

set GOOS=windows
set GOARCH=386
set CGO_ENABLED=1
go build -buildmode=c-shared -ldflags "-s -w -H=windowsgui" -o testDLL.dll main.go

VB6声明也需要调整，添加Alias和PtrSafe：

Declare Function GetIntFromDLL Lib "testDLL.dll" Alias "GetIntFromDLL@0" () As Long
Declare Function PrintHello Lib "testDLL.dll" Alias "PrintHello@8" (ByVal Nombre As String, ByRef Output As String) As Long
Declare Function PrintBye Lib "testDLL.dll" Alias "PrintBye@4" (ByRef Output As String) As Long
Declare Function LenString Lib "testDLL.dll" Alias "LenString@4" (ByVal Nombre As String) As Long
Declare Function OutString Lib "testDLL.dll" Alias "OutString@0" () As String

对于字符串参数处理，VB6端需要这样调用：

Private Sub TestDLL()
    Dim result As Long
    Dim outputBuffer As String
    Dim bufferSize As Long
    
    ' GetIntFromDLL
    result = GetIntFromDLL()
    Debug.Print "GetIntFromDLL: " & result
    
    ' PrintHello
    outputBuffer = String$(255, 0)
    bufferSize = PrintHello("Juan", outputBuffer)
    If bufferSize > 0 Then
        Debug.Print "PrintHello: " & Left$(outputBuffer, bufferSize)
    End If
    
    ' PrintBye
    outputBuffer = String$(255, 0)
    bufferSize = PrintBye(outputBuffer)
    If bufferSize > 0 Then
        Debug.Print "PrintBye: " & Left$(outputBuffer, bufferSize)
    End If
    
    ' LenString
    result = LenString("12345678")
    Debug.Print "LenString: " & result
    
    ' OutString
    Dim outStr As String
    outStr = OutString()
    Debug.Print "OutString: " & outStr
End Sub

关键点是：

1. Go导出函数时使用syscall.Syscall确保stdcall调用约定
2. 编译时使用-buildmode=c-shared生成标准的Windows DLL
3. VB6声明时使用正确的函数名修饰（name decoration），32位stdcall函数名格式为FunctionName@Bytes
4. 字符串参数需要预分配缓冲区并正确处理长度

这样修改后，VB6就能正确调用所有DLL函数了。