What is SafeFileHandle in c# and when should i use?

问题

While I am still learning System.IO, in File Stream class 's constructors, I found that there are overloaded constructors with the type named SafeFileHandle, I tried to search on the internet and the MSDN Documention, but I can't understand anything, and I found even stranger words, like IntPtr, can any one explain it to me?

public FileStream (Microsoft.Win32.SafeHandles.SafeFileHandle handle, System.IO.FileAccess access, int bufferSize, bool isAsync);

can someone explain it, or are there good websites that I can learn from..?

回答1:

https://docs.microsoft.com/en-us/dotnet/api/microsoft.win32.safehandles.safefilehandle?view=netframework-4.8

http://www.dotnetframework.org/default.aspx/DotNET/DotNET/8@0/untmp/whidbey/REDBITS/ndp/clr/src/BCL/Microsoft/Win32/SafeHandles/SafeFileHandle@cs/1/SafeFileHandle@cs

https://csharp.hotexamples.com/examples/-/SafeFileHandle/-/php-safefilehandle-class-examples.html

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwizlPG3ornlAhVFCKwKHUl9DxIQFjABegQIAxAB&url=https%3A%2F%2Fdocs.microsoft.com%2Fen-us%2Fdotnet%2Fapi%2Fmicrosoft.win32.safehandles.safefilehandle.-ctor&usg=AOvVaw3M0YPCVH1439KghalbcDfG

https://docs.microsoft.com/en-us/dotnet/api/system.io.filestream.safefilehandle?view=netframework-4.8

https://docs.microsoft.com/en-us/dotnet/api/microsoft.win32.safehandles.safefilehandle?redirectedfrom=MSDN&view=netframework-4.8

These links provide info on SafeFileHandle, and some provide source code.

You can also check this out: How to Close SafeFile Handle properly

IntPtr...

It's a "native (platform-specific) size integer." It's internally represented as void* but exposed as an integer. You can use it whenever you need to store an unmanaged pointer and don't want to use unsafe code. IntPtr.Zero is effectively NULL (a null pointer).

Pointer...

In general (across programming languages), a pointer is a number that represents a physical location in memory. A null pointer is (almost always) one that points to 0, and is widely recognized as "not pointing to anything". Since systems have different amounts of supported memory, it doesn't always take the same number of bytes to hold that number, so we call a "native size integer" one that can hold a pointer on any particular system.

SafeFileHandle kernel32...

[DllImport("kernel32.dll", SetLastError = true, CharSet=CharSet.Unicode)]
static extern SafeFileHandle CreateFile(string lpFileName, uint dwDesiredAccess,
  uint dwShareMode, IntPtr lpSecurityAttributes, uint dwCreationDisposition,
  uint dwFlagsAndAttributes, IntPtr hTemplateFile);

More with SafeFileHandle and kernel32...

[DllImport("kernel32.dll", SetLastError = true)]
static extern SafeFileHandle CreateFile(
string lpFileName,
uint dwDesiredAccess,
uint dwShareMode,
IntPtr lpSecurityAttributes,
uint dwCreationDisposition,
uint dwFlagsAndAttributes,
IntPtr hTemplateFile);
private SafeFileHandle handleValue = null;
handleValue = CreateFile(
Path,
GENERIC_WRITE,
0,
IntPtr.Zero,
OPEN_EXISTING,
0,
IntPtr.Zero);

Though, if you are trying to open a File, then use the System.IO Controls

To simply open a file and read all of it's text:

richTextBox1.Text = File.ReadAllText(yourfilename);

You can change the richTextBox1 to your Control's name.

I hope I am helping you, Prof Soft :)

来源：https://stackoverflow.com/questions/58568415/what-is-safefilehandle-in-c-sharp-and-when-should-i-use

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