C# FileInfo.Open method to read or write a file

We know that File.Open method is used to open a file (i.e. creating a stream) to read/write the file. Alos, the non-static FileInfo.Open methods can be used to read/write a file. FileInfo.Open has following overloads:

• public FileStream Open(FileMode mode, FileAccess access);
• public FileStream Open(FileStreamOptions options);
• public FileStream Open(FileMode mode, FileAccess access, FileShare share);
• public FileStream Open(FileMode mode);
• public FileStream OpenRead();
• public StreamReader OpenText();

FileMode enumerations:

• CreateNew = 1,
• Create = 2,
• Open = 3,
• OpenOrCreate = 4,
• Truncate = 5,
• Append = 6

FileAccess enumerations:

• Read = 1,
• Write = 2,
• ReadWrite = 3

Look at the following table to see different File Modes:

File Mode	Meaning
CreateNew = 1	Throws error if file exists
Create = 2	Overwrites if file exists
Open = 3	Throws error if file not found
OpenOrCreate = 4	Creates file if file not found
Truncate = 5	Opens an existing file and erase all of its contents immediately (set length to 0).
Append = 6	Opens file if it exists and seeks to the end of the file or creates a new file.

Look at the following table to see different File Access:

File Access	Meaning
Read	Can Read from a file
Write	Can Write into a file
ReadWrite	Can Read and Write a file

Example. Create mode

string desktop = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
string source_folder = Path.Combine(desktop, "source_folder");
string target_file = "sample.txt";

if (Directory.Exists(source_folder))
{
    FileInfo fileInfo = new FileInfo(Path.Combine(source_folder, target_file));
    // File will be overwritten if it already exists
    using FileStream fileStream = fileInfo.Open(FileMode.Create, FileAccess.Write);
    // Write "Hello World!" to the file
    fileStream.Write(System.Text.Encoding.UTF8.GetBytes("Hello World!"), 0, "Hello World!".Length);
    Console.WriteLine($"The {target_file} is created successfully.");
}

Example. CreateNew mode

string desktop = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
string source_folder = Path.Combine(desktop, "source_folder");
string target_file = "sample.txt";

if (Directory.Exists(source_folder))
{
    FileInfo fileInfo = new FileInfo(Path.Combine(source_folder, target_file));
    // Exception will be thrown if it already exists
    using FileStream fileStream = fileInfo.Open(FileMode.CreateNew, FileAccess.Write);
    // Write "Hello World!" to the file
    fileStream.Write(System.Text.Encoding.UTF8.GetBytes("Hello World!"), 0, "Hello World!".Length);
    Console.WriteLine($"The {target_file} is created successfully.");
}

Example. Open mode

string desktop = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
string source_folder = Path.Combine(desktop, "source_folder");
string target_file = "sample.txt";
string message = "Hello World!";
if (Directory.Exists(source_folder))
{
    FileInfo fileInfo = new FileInfo(Path.Combine(source_folder, target_file));
    // Exception will be thrown if file is missing
    using FileStream fileStream = fileInfo.Open(FileMode.Open, FileAccess.Write);
    // Write "Hello World!" to the file
    fileStream.Write(System.Text.Encoding.UTF8.GetBytes(message), 0, message.Length);
    Console.WriteLine($"The {target_file} is written successfully.");
}

Example. OpenOrCreate mode

string desktop = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
string source_folder = Path.Combine(desktop, "source_folder");
string target_file = "sample.txt";
string message = "Hello World!";
if (Directory.Exists(source_folder))
{
    FileInfo fileInfo = new FileInfo(Path.Combine(source_folder, target_file));
    // a new file will be created if file is missing
    using FileStream fileStream = fileInfo.Open(FileMode.OpenOrCreate, FileAccess.Write);
    // Write "Hello World!" to the file
    fileStream.Write(System.Text.Encoding.UTF8.GetBytes(message), 0, message.Length);
    Console.WriteLine($"The {target_file} is written successfully.");
}

Example. Append mode 

string desktop = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
string source_folder = Path.Combine(desktop, "source_folder");
string target_file = "sample.txt";
string message = "Hello World!";
if (Directory.Exists(source_folder))
{
    FileInfo fileInfo = new FileInfo(Path.Combine(source_folder, target_file));
    // Exception will be thrown if file is missing
    using FileStream fileStream = fileInfo.Open(FileMode.Append, FileAccess.Write);
    // Append "Hello World!" to the file
    fileStream.Write(System.Text.Encoding.UTF8.GetBytes(message), 0, message.Length);
    Console.WriteLine($"The {target_file} is written successfully.");
}

Notes. 

1. Change the FieAccess.Write to FileAccess.Read to perform Read operation on file.
2. FieAccess mode is optional. You can even use Open(FileMode mode) to create FileStream.
3. To read a text file, you can use OpenText method which returns StreamReader.

Example. OpenText method

string desktop = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
string source_folder = Path.Combine(desktop, "source_folder");
string target_file = "sample.txt";
if (Directory.Exists(source_folder))
{
    FileInfo fileInfo = new FileInfo(Path.Combine(source_folder, target_file));
    using StreamReader reader = fileInfo.OpenText();
    string allData = reader.ReadToEnd();
    Console.WriteLine($"The {target_file} contains:\n {allData}");
}