c++ - 系统调用 GetLastError() 不返回错误

Question

在 golang 中 syscall.GetLastError() 不返回最后一个错误。看下面的例子

if handle := _OpenSCManager(machineNamePtr, databaseNamePtr, desiredAccess); handle == nil {
    if err := syscall.GetLastError(); err != nil {
        return InvalidServiceDatabaseHandleHandle, ServiceErrno(err.(syscall.Errno))
    }
}

err 始终为 nil。假设 machineNamePtr 是一台不存在的机器。使用 C++ 测试了相同的代码，GetLastError() 抛出 RPC 服务器不可用。那为什么不 go 呢？

编辑

_OpenSCManager 是用go generate 生成的。//sys _OpenSCManager(machineName *uint16, databaseName *uint16, desiredAccesss ServiceAccessRight) (句柄 ServiceDatabaseHandle) = advapi32.OpenSCManagerW

func _OpenSCManager(machineName *uint16, databaseName *uint16, desiredAcces ServiceAccessRight) (handle ServiceDatabaseHandle) {
r0, _, _ := syscall.Syscall(procOpenSCManagerW.Addr(), 3, uintptr(unsafe.Pointer(machineName)), uintptr(unsafe.Pointer(databaseName)), uintptr(desiredAcces))
handle = ServiceDatabaseHandle(r0)
return

Answer 1

所以我终于成功了。首先，我尝试返回一个具有以下签名的错误变量 //sys _OpenSCManager(machineName *uint16, databaseName *uint16, desiredAcces ServiceAccessRight) (handle ServiceDatabaseHandle, lasterror error) = advapi32.OpenSCManagerW。但是 go generate 总是抛出 Only last windows error is allowed as second return value...。但是，如果将其更改为 //sys ... (handle ServiceDatabaseHandle, err error) = advapi32.OpenSCManagerW 它会成功生成代码。所以你必须明确地写err error。有人知道为什么吗？所以现在函数看起来像

func _OpenSCManager(machineName *uint16, databaseName *uint16, desiredAcces ServiceAccessRight) (handle ServiceDatabaseHandle, err error) {
r0, _, e1 := syscall.Syscall(procOpenSCManagerW.Addr(), 3, uintptr(unsafe.Pointer(machineName)), uintptr(unsafe.Pointer(databaseName)), uintptr(desiredAcces))
handle = ServiceDatabaseHandle(r0)
if handle == 0 {
    if e1 != 0 {
        err = errnoErr(e1)
    } else {
        err = syscall.EINVAL
    }
}
return
}

它返回一个错误。因此无需调用 GetLastError()。