Read CSV from variable using CsvHelper (or similar library)

Question

I've got a function that makes something equivalent to a web request, and it returns a formatted CSV. My goal is to now import this data into CsvHelper. However, I can't seem to get CSVParser to read from static text, only from a stream.

I could write the output to a file then read it back, but I feel that doesn't make much sense here.

I'm not tied down at all to CsvHelper, however I can't seem to find a CSV library that supports this behavior. How should I do this?

var csvString = functionThatReturnsCsv()
/* as string:
columnA,columnB
dataA,dataB
*/

// my goal
???.parse(csvString)

Note (to anyone visiting this question and looking at the answers) that using a StringReader (as shown by David Specht's answer) is the approach that is more convenient, and leads to simpler and ultimately more readable code compared to converting the string to a byte array to a MemoryStream. After all, any CSV parser would need to translate the byte stream back into text characters anyway. (A CSV parser not accepting a text source in some form - for example, a TextReader - is not really worth considering, imo) — user2819245
– user2819245, Commented Jun 6, 2019 at 19:24

ProgrammingLlama · Accepted Answer · 2019-06-04 02:15:58Z

5

You can convert the string to a Stream in-memory and then use that as the source for your CSV reader:

public static Stream StringAsStream(string value)
{
    return StringAsStream(value, System.Text.Encoding.UTF8);
}

public static Stream StringAsStream(string value, System.Text.Encoding encoding)
{
    var bytes = encoding.GetBytes(value);
    return new MemoryStream(bytes);
}

Usage:

using (var stream = StringAsStream("hello"))
{
    // csv reading code here
}

or

using (var stream = StringAsStream("hello", Encoding.Ascii))
{
    // csv reading code here
}

Try it online

Note If you are reading from a source that can return a Stream (like a web request), you should use that Stream rather than doing this.

answered Jun 4, 2019 at 2:15

ProgrammingLlama

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4 Comments

I Yam Who I Yam Over a year ago

Can I ask why you're using a using directive here rather than just using the var in the code?

ProgrammingLlama Over a year ago

While you don't need to use Dispose with MemoryStream, it's good practice for any Stream you consume since they typically represent unmanaged resources (the garbage collector can't collect these). using will automatically clal Dispose once the using block completes - even in the event of an exception. See here for more info on what using does.

I Yam Who I Yam Over a year ago

Ok. So if I wanted to make a function that would return the stdout of another program, I would return the standard output from the using definition, correct? (like this rextester.com/VII34075)

I Yam Who I Yam Over a year ago

That's what I ended up doing and it worked. Thanks for your help!

David Specht · Accepted Answer · 2019-06-06 19:17:51Z

4

You could use StringReader. The CsvReader constructor takes a TextReader argument rather than a Stream. If you did have a stream instead of a string, just replace StringReader with StreamReader.

public static void Main(string[] args)
{    
    using (var reader = new StringReader(FunctionThatReturnsCsv()))
    using (var csv = new CsvReader(reader))
    {
        var results = csv.GetRecords<Foo>().ToList();
    }            
}

public static string FunctionThatReturnsCsv()
{
    return "columnA,columnB\ndataA,dataB";
}

public class Foo
{
    public string columnA { get; set; }
    public string columnB { get; set; }
}

edited Jun 6, 2019 at 19:17

answered Jun 5, 2019 at 17:12

David Specht

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