vb中怎么使用形参为指针的Api？

[Quantumquark]

比如Enumjobs，我直接使用得到需要使用的缓冲区大小后再指定缓冲区大小，代码运行到这里vb就退出。请问高手如何解决？

[zyl910]

ByRef

• 打赏
• 举报

回复 赞

[zyl910]

给我看看那个函数的原型定义
我现在在网吧，没有MSDN

• 打赏
• 举报

回复 赞

[rainstormmaster]

取得地址后，用byval也可

• 打赏
• 举报

回复 赞

[hwyqy]

忘了Enumjobs怎么用，但VB中可以运用指针。
如要指定一个函数的地址（称为回调），用AddressOf（函数名），如a(3,addrssof(b))，AddrssOf后面的函数必须在标准模块中。
如用变量的地址，VB中有函数VarPtr（得数值变量地址）和StrPtr（得字符串变量地址）可以得到变量的地址
如：dim a as integer
dim b as long
b=varptr(a)
call add(byval b)
回为b包含的是地址信息，所以用byval。
关于strptr较复杂，建议不要使用。传字符串地址直接用byval 变量名就行。

• 打赏
• 举报

回复 赞

[zyl910]

http://www.mentalis.org/apilist/032700B745AB7E90AAB51EA25999E3B2.html

• 打赏
• 举报

回复 赞

[rainstormmaster]

如何得知某一台网络打印机尚有几份等待打印的报表？
当我们要打印报表时，如果打印机是本机的打印机的话，当然马上就会将报表打印出来，反正打印机就只有您一个人在使用而已！但是如果是在一个人数很多的公司或企业时，往往就必须很多人来分享某一部打印机了，而且打印机也不一定就放在举目可及之处！

当您将报表丢到网络打印机之后，由于不一定看得到打印机，您必须特别到摆放打印机的地方去拿报表，这时候您最关心的，就是报表印了没有，如果还没有的话，那还有几份还没打印的报表排在您的报表之前呢？

下面这一段程序，可以让您知道某一台网络打印机尚有几份等待打印的报表？在您的程序丢出报表的同时，您可以告诉您的 User，他的报表排在第几份！

'在 .bas 文件中加入以下声明及模组：

'Constants Definition
Public Const CCHDEVICENAME = 32
Public Const CCHFORMNAME = 32
Public Const PRINTER_ACCESS_ADMINISTER = &H4
Public Const PRINTER_ACCESS_USE = &H8

'Types Definition
Public Type DEVMODE
dmDeviceName As String * CCHDEVICENAME
dmSpecVersion As Integer
dmDriverVersion As Integer
dmSize As Integer
dmDriverExtra As Integer
dmFields As Long
dmOrientation As Integer
dmPaperSize As Integer
dmPaperLength As Integer
dmPaperWidth As Integer
dmScale As Integer
dmCopies As Integer
dmDefaultSource As Integer
dmPrintQuality As Integer
dmColor As Integer
dmDuplex As Integer
dmYResolution As Integer
dmTTOption As Integer
dmCollate As Integer
dmFormName As String * CCHFORMNAME
dmUnusedPadding As Integer
dmBitsPerPel As Long
dmPelsWidth As Long
dmPelsHeight As Long
dmDisplayFlags As Long
dmDisplayFrequency As Long
End Type

Public Type PRINTER_DEFAULTS
pDatatype As String
pDevMode As DEVMODE
DesiredAccess As Long
End Type

'API Declarations
Public Declare Function OpenPrinter Lib "winspool.drv" Alias "OpenPrinterA" (ByVal pPrinterName As String, phPrinter As Long, pDefault As PRINTER_DEFAULTS) As Long
Public Declare Function EnumJobs Lib "winspool.drv" Alias "EnumJobsA" (ByVal HPrinter As Long, ByVal FirstJob As Long, ByVal NoJobs As Long, ByVal Level As Long, pJob As Byte, ByVal cdBuf As Long, pcbNeeded As Long, pcReturned As Long) As Long

Public Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long

'取得指定的打印机，目前有多少 Jobs (最大值为 128)
'打印机的名称可以是 mapping 的网络路径名称，例如： "\\myserver\myprinter"
Function GetPrinterQueue(PrinterName As String) As Long
Dim PrinterStruct As PRINTER_DEFAULTS
Dim HPrinter As Long
Dim ret As Boolean
Dim JobStruct(0 To 127) As Byte
Dim pcbNeeded As Long
Dim pcReturned As Long
Dim TempByte As Byte

'设定 Printer structure 初值
PrinterStruct.pDatatype = vbNullString
PrinterStruct.pDevMode.dmSize = Len(PrinterStruct.pDevMode)
PrinterStruct.DesiredAccess = PRINTER_ACCESS_USE
'取得打印机的 Handle
ret = OpenPrinter(PrinterName, HPrinter, PrinterStruct)
'取得打印机的 active jobs
ret = EnumJobs(HPrinter, 0, 127, 1, TempByte, 0, pcbNeeded, pcReturned)
If pcbNeeded = 0 Then
GetPrinterQueue = 0
Else
ret = EnumJobs(HPrinter, 0, 127, 1, JobStruct(0), pcbNeeded, pcbNeeded, pcReturned)
GetPrinterQueue = pcReturned
End If
'关闭打印机
ret = CloseHandle(HPrinter)
End Function

'在表单中放一个 CommandButton，程序码如下：

Private Sub Command1_Click()
'测试预设打印机的 Queue (Printer.DeviceName)
Msgbox "打印机中尚有 " & GetPrinterQueue(Printer.DeviceName) & " 份报表", 64, "讯息"
End Sub

'好了，试试看吧！

• 打赏
• 举报

回复 赞

[Quantumquark]

zyl910(910：分儿，我又来了！) :谢谢！下面是api声明：

Public Declare Function EnumJobs Lib "winspool.drv" Alias "EnumJobsA" (ByVal hPrinter As Long, ByVal FirstJob As Long, ByVal NoJobs As Long, ByVal Level As Long, pJob As Byte, ByVal cdBuf As Long, pcbNeeded As Long, pcReturned As Long) As Long

pJob As Byte 这个指针指向Job_Info结构的缓冲区，不知道如何使用

########################################################
rainstormmaster(rainstormmaster)：谢谢！我正在试。

• 打赏
• 举报

回复 赞

[zyl910]

你自己不知道改一下声明啊


Public Declare Function EnumJobs Lib "winspool.drv" Alias "EnumJobsA" (ByVal hPrinter As Long, ByVal FirstJob As Long, ByVal NoJobs As Long, ByVal Level As Long, Byref pJob As Job_Info, ByVal cdBuf As Long, pcbNeeded As Long, pcReturned As Long) As Long




Dim Jobs(1 to 10) as Job_Info
EnumJobs hPrinter, FirstJob, NoJobs, Level, Jobs(1), len(Jobs(1))*10, pcbNeeded, pcReturned

• 打赏
• 举报

回复 赞

[Quantumquark]

我改过声明，但一运行到指定缓冲区大小（cdBuf&=pcNeeded&）到时候就发生：“Vb6发生错误（KERNEL32.DLL)。Vb6即将退出。”然后就退出。

rainstormmaster(rainstormmaster)：你给我的这段代码有时候发生上面说的错误。有时候不发生。

• 打赏
• 举报

回复 赞

[海牛]

学习ing

• 打赏
• 举报

回复 赞

[Quantumquark]

还是不太稳定，结贴了。谢谢各位。

• 打赏
• 举报

回复 赞