WINAPI FindFirstFile & FindNextFile problem

Jorge

15y7kVisual Basic .NET

Hi all,

I'm trying to get the list of files in a directory using WINAPI functions FindFirstFile and FindNextFile.

The problem is that WIN32_FIND_DATA.cFileName returns only the first character of the file name.

This is a console application created in Microsoft Visual C# 2008 Express Edition.

Here is the code. Do you have any ideas what is wrong?

Thanks

using System;

using System.IO;

using System.Runtime.InteropServices;

namespace DirectoryWINAPI

{

struct WIN32_FIND_DATA

{

public uint dwFileAttributes;

public System.Runtime.InteropServices.ComTypes.FILETIME ftCreationTime;

public System.Runtime.InteropServices.ComTypes.FILETIME ftLastAccessTime;

public System.Runtime.InteropServices.ComTypes.FILETIME ftLastWriteTime;

public uint nFileSizeHigh;

public uint nFileSizeLow;

public uint dwReserved0;

public uint dwReserved1;

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]

public string cFileName;

[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 14)]

public string cAlternateFileName;

}

class Program

{

[DllImport("kernel32", CharSet = CharSet.Auto)]

public static extern IntPtr FindFirstFile(string lpFileName, out WIN32_FIND_DATA lpFindFileData);

[DllImport("kernel32", CharSet = CharSet.Auto)]

public static extern bool FindNextFile(IntPtr hFindFile, out WIN32_FIND_DATA lpFindFileData);

[DllImport("kernel32", CharSet = CharSet.Auto)]

public static extern bool FindClose(IntPtr hFindFile);

static void Main(string[] args)

{

StreamWriter sw = new StreamWriter("dir.txt", false);

string dir = Path.GetFullPath(System.IO.Directory.GetCurrentDirectory());

WIN32_FIND_DATA wfd = new WIN32_FIND_DATA();

IntPtr h = FindFirstFile((dir + @"\*.*"), out wfd);

while (FindNextFile(h, out wfd))

sw.WriteLine(wfd.cFileName);

FindClose(h);

sw.Flush();

sw.Close();

}

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes15y ago
Accepted answer
I've just been playing around with this some more and found that if you add the following attribute to the struct in your original program then it works fine!

[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Auto)]

I think this is because you're using the CharSet.Auto versions of the functions which default to ANSI. As there was no attribute, the strings would have been marshalled to unicode.
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Jorge15y ago
Thank you very much, Vulpes! Your first reply worked with one minor adjustment, I only had to trim the trailing nulls from the string in the line: sw.WriteLine(Encoding.Unicode.GetString(wfd.cFileName)); The second reply was spot on! Thanks again
0
Vulpes15y ago
I think the problem there is that the API functions are unable to write properly to the strings within the struct bearing in mind that strings are immutable in .NET. StringBuilder doesn't work either but I did manage to get it to work using byte arrays (changes are commented):

using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Text; // added this

namespace DirectoryWINAPI
{
[StructLayout(LayoutKind.Sequential)] // added this
struct WIN32_FIND_DATA
{
public uint dwFileAttributes;
public System.Runtime.InteropServices.ComTypes.FILETIME ftCreationTime;
public System.Runtime.InteropServices.ComTypes.FILETIME ftLastAccessTime;
public System.Runtime.InteropServices.ComTypes.FILETIME ftLastWriteTime;
public uint nFileSizeHigh;
public uint nFileSizeLow;
public uint dwReserved0;
public uint dwReserved1;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 260)] // change here
public byte[] cFileName; // ditto
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 14)] // ditto
public byte[] cAlternateFileName; // ditto
}

class Program
{
[DllImport("kernel32", CharSet = CharSet.Auto)]
public static extern IntPtr FindFirstFile(string lpFileName, out WIN32_FIND_DATA lpFindFileData);

[DllImport("kernel32", CharSet = CharSet.Auto)]
public static extern bool FindNextFile(IntPtr hFindFile, out WIN32_FIND_DATA lpFindFileData);

[DllImport("kernel32", CharSet = CharSet.Auto)]
public static extern bool FindClose(IntPtr hFindFile);

static void Main(string[] args)
{
StreamWriter sw = new StreamWriter("dir.txt", false);
string dir = Path.GetFullPath(System.IO.Directory.GetCurrentDirectory());
WIN32_FIND_DATA wfd = new WIN32_FIND_DATA();
IntPtr h = FindFirstFile((dir + @"\*.*"), out wfd);
while (FindNextFile(h, out wfd))
sw.WriteLine(Encoding.Unicode.GetString(wfd.cFileName)); // change here
FindClose(h);
sw.Flush();
sw.Close();
}
}
}
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