WinRT No mapping for the Unicode character exists in the target multi-byte code page - file-io

Question

I am trying to read a file in my Windows 8 Store App. Here is a fragment of code I use to achieve this:
if(file != null)
{
var stream = await file.OpenAsync(FileAccessMode.Read);
var size = stream.Size;
using(var inputStream = stream.GetInputStreamAt(0))
{
DataReader dataReader = new DataReader(inputStream);
uint numbytes = await dataReader.LoadAsync((uint)size);
string text = dataReader.ReadString(numbytes);
}
}
However, an exeption is thrown at line:
string text = dataReader.ReadString(numbytes);
Exeption message:
No mapping for the Unicode character exists in the target multi-byte code page.
How do I get by this?

Answer 1

I managed to read file correctly using similar approach to suggested by duDE:
if(file != null)
{
IBuffer buffer = await FileIO.ReadBufferAsync(file);
DataReader reader = DataReader.FromBuffer(buffer);
byte[] fileContent = new byte[reader.UnconsumedBufferLength];
reader.ReadBytes(fileContent);
string text = Encoding.UTF8.GetString(fileContent, 0, fileContent.Length);
}
Can somebody please elaborate, why my initial approach didn't work?

Answer 2

Try this instead of string text = dataReader.ReadString(numbytes):
dataReader.ReadBytes(stream);
string text = Convert.ToBase64String(stream);

Answer 3

If, like me, this was the top result when search for the same error regarding UWP, see the below:
The code I had which was throwing the error (no mapping for the unicode character exists..):
var storageFile = await Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.GetFileAsync(fileToken);
using (var stream = await storageFile.OpenAsync(FileAccessMode.Read))
{
using (var dataReader = new DataReader(stream))
{
await dataReader.LoadAsync((uint)stream.Size);
var json = dataReader.ReadString((uint)stream.Size);
return JsonConvert.DeserializeObject<T>(json);
}
}
What I changed it to so that it works correctly
var storageFile = await Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.GetFileAsync(fileToken);
using (var stream = await storageFile.OpenAsync(FileAccessMode.Read))
{
T data = default(T);
using (StreamReader astream = new StreamReader(stream.AsStreamForRead()))
using (JsonTextReader reader = new JsonTextReader(astream))
{
JsonSerializer serializer = new JsonSerializer();
data = (T)serializer.Deserialize(reader, typeof(T));
}
return data;
}