VBA使用API_01：读取文件

Open pathname For mode [ Access access ] [ lock ] As [ # ] filenumber [ Len = reclength ]

Public Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, ByVal lpSecurityAttributes As Long, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long
Public Declare Function ReadFile Lib "kernel32" (ByVal hFile As Long, ByVal lpBuffer As Long, ByVal nNumberOfBytesToRead As Long, ByRef lpNumberOfBytesRead As Long, ByVal lpOverlapped As Long) As Long
Public Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long

'lpFileName         文件名
'dwDesiredAccess    访问模式
Const GENERIC_READ As Long = &H80000000
Const GENERIC_WRITE As Long = &H40000000

'dwShareMode        共享模式，意思就是当前进程打开之后，还允许其他程序做什么，0就是独占了
Const FILE_SHARE_DELETE As Long = &H4
Const FILE_SHARE_READ As Long = &H1
Const FILE_SHARE_WRITE As Long = &H2

'lpSecurityAttributes   安全属性(也即销毁方式),     为NULL，句柄就不能被子进程继承。
Type SECURITY_ATTRIBUTES
    nLength As Long
    lpSecurityDescriptor As Long
    bInheritHandle As Long
End Type

'dwCreationDisposition  how to create
Const CREATE_NEW As Long = &H1  ' 创建新文件/对象(当对象已经存在是将返回失败)。
Const CREATE_ALWAYS As Long = &H2 ' 总是创建(如果对象存在就覆盖它，清除当前属性，把文件属性和dwFlagsAndAttributes指定的标志相结合)。
Const OPEN_EXISTING As Long = 3  ' 打开文件(如果不存在就返回失败)。
Const OPEN_ALWAYS As Long = &H4 ' 存在就打开；若不存在，假如dwCreationDisposition==CREATE_NEW就创建一个新文件。
Const TRUNCATE_EXISTING As Long = &H5 ' 存在就打开，且清空文件内容(至少要有GENERIC_WRITE权限)；若文件不存在就返回失败。

'dwFlagsAndAttributes   文件属性
Const FILE_ATTRIBUTE_READONLY  As Long = &H1
Const FILE_ATTRIBUTE_NORMAL As Long = &H80

'hTemplateFile  模板文件句柄

Const INVALID_HANDLE_VALUE As Long = -1
'成功返回文件句柄
'失败返回INVALID_HANDLE_VALUE
Public Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" (ByVal lpFileName As String, ByVal dwDesiredAccess As Long, ByVal dwShareMode As Long, ByVal lpSecurityAttributes As Long, ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long, ByVal hTemplateFile As Long) As Long

'dwMoveMethod
Const FILE_BEGIN As Long = 0
Const FILE_CURRENT As Long = 1
Const FILE_END As Long = 2
Public Declare Function SetFilePointer Lib "kernel32" (ByVal hFile As Long, ByVal lDistanceToMove As Long, lpDistanceToMoveHigh As Long, ByVal dwMoveMethod As Long) As Long

'lpSecurityAttributes As SECURITY_ATTRIBUTES


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

'lpBuffer        用来接收从文件中读出的数据的缓冲区指针
'nNumberOfBytesToRead    指明要读的字节总数
'lpNumberOfBytesRead    一个变量指针，用来存储实际传输的字节总数
'如果函数正确，返回非零。
Public Declare Function ReadFile Lib "kernel32" (ByVal hFile As Long, ByVal lpBuffer As Long, ByVal nNumberOfBytesToRead As Long, ByRef lpNumberOfBytesRead As Long, ByVal lpOverlapped As Long) As Long

'lpOverlapped As OVERLAPPED
Type OVERLAPPED
    Internal As Long
    InternalHigh As Long
    offset As Long
    OffsetHigh As Long
    hEvent As Long
End Type

Sub TestAPIReadFile()
    Dim hFile As Long

    hFile = CreateFile(ThisWorkbook.Path & "\test.txt", GENERIC_READ, 0, 0, OPEN_EXISTING, 0, 0)
    If hFile = INVALID_HANDLE_VALUE Then
        Debug.Print "open出错"
        Exit Sub
    End If
    
    Dim ret As Long

    Dim b() As Byte
    Dim nNumberOfBytesToRead As Long
    nNumberOfBytesToRead = 32
    ReDim b(nNumberOfBytesToRead - 1) As Byte

    Dim retlen As Long
    ret = ReadFile(hFile, VarPtr(b(0)), nNumberOfBytesToRead, retlen, 0)
    If ret = 0 Then
        Debug.Print "read出错"
        CloseHandle hFile
        Exit Sub
    End If
    Printf "文件读取成功：读的字节总数%d， 实际读取字节总数%d，%s", nNumberOfBytesToRead, retlen, VBA.StrConv(b, vbUnicode)

    CloseHandle hFile
End Sub