Does Disposing a StreamReader Also Close the Underlying Stream?

Close of StreamReader and underlying stream: detailed explanation and best practices

When working with streams in programming, you typically use StreamReader to perform a specific task, such as reading lines from a text file. However, a common question is: does the release of the StreamReader object affect the closing of the underlying stream?

Answer: Yes.

Release StreamReader (as well as StreamWriter, BinaryReader and BinaryWriter) triggers the closing and release of the underlying stream. This happens when the Dispose methods of these reader and writer objects are explicitly called. However, these classes do not free the stream through garbage collection. Therefore, be sure to manually release the reader/writer instance using the using statement to ensure the stream is closed properly.

Best Practices:

To ensure consistent release of the stream, it is recommended to directly use the using statement to manage the stream itself. The desired release behavior can be elegantly achieved by using nested using statements to manage streams and readers and writers, as shown below:

using (Stream stream = ...)
using (StreamReader reader = new StreamReader(stream, Encoding.Whatever))
{
    // 使用 reader 读取数据
}

Even though the stream statement for using may seem redundant, this approach is strongly recommended given the exceptions that may occur during StreamReader instantiation. Doing this ensures that the stream is released correctly even if the StreamReader is removed or later replaced by using the stream directly.

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