程序代码：

Option Explicit
Private Declare Function GetOpenFileName Lib "comdlg32.dll" Alias "GetOpenFileNameA" (pOpenfilename As OPENFILENAME) As Long
Private Const OFN_PATHMUSTEXIST = &H800     '路径必须存在
Private Const OFN_FILEMUSTEXIST = &H1000    '文件必须存在

'' OPENFILENAME 结构的元素顺序必须按vb6自带的api浏览器里的格式声明。按foxApi V1.5里的声明时出错
Private Type OPENFILENAME

    lStructSize     As Long
    hwndOwner       As Long
    hInstance       As Long
    lpstrFilter     As String
    lpstrCustomFilter As String
    nMaxCustFilter  As Long
    nFilterIndex    As Long
    lpstrFile       As String
    nMaxFile        As Long
    lpstrFileTitle  As String
    nMaxFileTitle   As Long
    lpstrInitialDir As String
    lpstrTitle      As String
    flags           As Long
    nFileOffset     As Integer
    nFileExtension  As Integer
    lpstrDefExt     As String
    lCustData       As Long
    lpfnHook        As Long
    lpTemplateName  As String

End Type

Public Function ShowOpen(ByVal hwndOwner As Long, Optional ByVal strTitle As String = "打开...", Optional ByVal lpstrFilter As String = "All Files(*.*)" & vbNullChar & "*.*" & vbNullChar, Optional ByVal initDir As String = "c:\", Optional ByVal defExt As String = "*.JTF") As String

    On Error Resume Next

    Dim OFName As OPENFILENAME
    OFName.lStructSize = Len(OFName)
    OFName.hwndOwner = hwndOwner
    OFName.lpstrFilter = lpstrFilter
    OFName.lpstrFile = Space$(254)
    OFName.nMaxFile = 255
    OFName.lpstrFileTitle = Space$(254)
    OFName.nMaxFileTitle = 255
    OFName.lpstrInitialDir = initDir
    OFName.lpstrTitle = strTitle
    OFName.lpstrDefExt = defExt
    OFName.flags = OFN_FILEMUSTEXIST Or OFN_PATHMUSTEXIST

    'Debug.Print OFName.nFileExtension
    If GetOpenFileName(OFName) Then
        ShowOpen = Trim$(OFName.lpstrFile)
    Else
        ShowOpen = ""
    End If

End Function