CODEWITHSUNDEEP
c#streamfilestreamdacbacpac
CodeMonkey
CodeMonkey

Reputation: 12444

Difference between loading a file from a path and from a stream C#

This is a follow up question to this question:

Difference between file path and file stream?

I didn't fully understand everything answered in the linked question.

I am using the Microsoft.SqlServer.Dac.BacPackage which contains a Load method with 2 overloads - one that receives a string path and one that receives a Stream.

This is the documentation of the Load method:

https://learn.microsoft.com/en-us/dotnet/api/microsoft.sqlserver.dac.bacpackage.load?view=sql-dacfx-150

What exactly is the difference between the two? Am I correct in assuming that the overloading of the string path saves all the file in the memory first, while the stream isn't? Are there other differences?

Upvotes: 0

Views: 1188

Answers (2)

Harald Coppoolse
Harald Coppoolse

Reputation: 30474

Short answer:

The fact that you have two methods, one that accepts a filename and one that accepts a stream is just for convenience. Internally, the one with the filename will open the file as a stream and call the other method.

Longer answer

You can consider a stream as a sequence of bytes. The reason to use a stream instead of a byte[] or List<byte>, is, that if the sequence is really, really large, and you don't need to have access to all bytes at once, it would be a waste to put all bytes in memory before processing them.

For instance, if you want to calculate the checksum for all bytes in a file: you don't need to put all data in memory before you can start calculating the sum. In fact, anything that efficiently can deliver you the bytes one by one would suffice.

That is the reason why people would want to read a file as a stream.

The reason why people want a stream as input for their data, is that they want to give the caller the opportunity to specify the source of their data: callers can provide a stream that reads from a file, but also a stream with data from the internet, or from a database, or from a textBox, the procedure does not care, as long as it can read the bytes one by one or sometimes per chunk of bytes:

using (Stream fileStream = File.Open(fileName)
{
    ProcessInputData(fileStream);
}

Or:

byte[] bytesToProcess = ...
using (Stream memoryStream = new MemoryStream(bytesToProcess))
{
    ProcessInputData(memoryStream);
}

Or:

string operatorInput = this.textBox1.Text;
using (Stream memoryStream = new MemoryStream(operatorInput))
{
    ProcessInputData(memoryStream);
}

Conclusioin

Methods use streams in their interface to indicate that they don't need all data in memory at once. One-by-one, or per chunk is enough. The caller is free to decide where the data comes from.

Upvotes: 0

Charlieface
Charlieface

Reputation: 72087

No, the file will not usually be fully loaded all at once.

A string path parameter normally means it will just open the file as a FileStream and pass it to the other version of the function. There is no reason why the stream should fully load the file into memory unless requested.

A Stream parameter means you open the file and pass the resulting Stream. You could also pass any other type of Stream, such as a network stream, a zip or decryption stream, a memory-backed stream, anything really.

Upvotes: 0

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