Does Microsoft provide API for appending binary data to file end?

Question

I can use AppendTextAsync(IStorageFile, String, UnicodeEncoding) to append text to file (https://learn.microsoft.com/en-us/uwp/api/windows.storage.fileio.appendtextasync?view=winrt-22621). Does Microsoft provide API for appending binary data to file end?

Answer 1

You can use BinaryWriter:

using FileStream fs = new FileStream(@".\Test.bin", FileMode.Append, FileAccess.Write);
using BinaryWriter bw = new BinaryWriter(fs);

bw.Write(new byte[] { 0x01, 0x02, 0x03 });
bw.Write(new byte[] { 0x04, 0x05, 0x06 });

Note the FileStream has been opened with FileMode.Append.

Answer 2

Hi @longevity uyl ,

Welcome to Microsoft Q&A!

Due to the file permissions of UWP, it is recommended that you use ApplicationData.Current.LocalFolder to access files in the folder.

Use OpenStreamForWriteAsync to open stream and use WriteAsync to write binary data to file end.

StorageFolder localFolder = ApplicationData.Current.LocalFolder;
StorageFile saveFile = await localFolder.CreateFileAsync("FileIOtest.txt", CreationCollisionOption.OpenIfExists);

await FileIO.AppendTextAsync(saveFile, "hello world");

String s = "binary data";
Byte[] bytes = Encoding.UTF8.GetBytes(s);

using (Stream stream = await ApplicationData.Current.LocalFolder.OpenStreamForWriteAsync
    ("FileIOtest.txt", CreationCollisionOption.OpenIfExists))
{
    stream.Seek(0, SeekOrigin.End);
    await stream.WriteAsync(bytes, 0, bytes.Length);
}

Thank you.