File.Open Method (String, FileMode, FileAccess)


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Opens a FileStream on the specified path, with the specified mode and access.

Namespace:   System.IO
Assembly:  mscorlib (in mscorlib.dll)

static member Open : 
        path:string *
        mode:FileMode *
        access:FileAccess -> FileStream


Type: System.String

The file to open.

Type: System.IO.FileMode

A FileMode value that specifies whether a file is created if one does not exist, and determines whether the contents of existing files are retained or overwritten.

Type: System.IO.FileAccess

A FileAccess value that specifies the operations that can be performed on the file.

Return Value

Type: System.IO.FileStream

An unshared FileStream that provides access to the specified file, with the specified mode and access.

Exception Condition

path is a zero-length string, contains only white space, or contains one or more invalid characters as defined by InvalidPathChars.


access specified Read and mode specified Create, CreateNew, Truncate, or Append.


path is null.


The specified path, file name, or both exceed the system-defined maximum length. For example, on Windows-based platforms, paths must be less than 248 characters, and file names must be less than 260 characters.


The specified path is invalid, (for example, it is on an unmapped drive).


An I/O error occurred while opening the file.


path specified a file that is read-only and access is not Read.


path specified a directory.


The caller does not have the required permission.


mode is Create and the specified file is a hidden file.


mode or access specified an invalid value.


The file specified in path was not found.


path is in an invalid format.

The path parameter is permitted to specify relative or absolute path information. Relative path information is interpreted as relative to the current working directory. To obtain the current working directory, see GetCurrentDirectory.

The following example opens a file with read-only access.

No code example is currently available or this language may not be supported.


for reading from and writing to the specified file. Associated enumerations: FileIOPermissionAccess.Read, FileIOPermissionAccess.Write

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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