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Editorial Team
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Asked: 2026-05-13T13:01:12+00:00

While opening a file in C# using stream reader is the file going to

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While opening a file in C# using stream reader is the file going to remain in memory till it closed.
For eg if a file of size 6MB is opened by a program using streamreader to append a single line at the end of the file. Will the program hold the entire 6 MB in it’s memory till file is closed. OR is a file pointer returned internally by .Net code and the line is appended at the end. So the 6MB memory will not be taken up by the program

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1 Answer

  1. Editorial Team

    A StreamReader uses FileStream to open the file. FileStream stores a Windows handle, returned by the CreateFile() API function. It is 4 bytes on a 32-bit operating system. FileStream also has a byte[] buffer, it is 4096 bytes by default. This buffer avoids having to call the ReadFile() API function for every single read call. StreamReader itself has a small buffer to make decoding the text in the file more efficient, it is 128 bytes by default. And it has some private variables to keep track of the buffer index and whether or not a BOM has been detected.

    This all adds up to a few kilobytes. The data you read with StreamReader will of course take space in your program’s heap. That could add up to 12 megabytes if you store every string in, say, a List. You usually want to avoid that.

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