How to convert CSV to XLSX in C# and .NET: A step-by-step Guide

Step-by-step guide:

  1. Add SautinSoft.Excel from Nuget.
  2. Load an input document.
  3. Save to a XLSX format.

Complete code

using SautinSoft.Excel;
using System.IO;

namespace Example
{
    class Program
    {
        static void Main(string[] args)
        {
            // Get your free key here:   
            // https://sautinsoft.com/start-for-free/

            ConvertFromFile();
            ConvertFromStream();
        }

        /// <summary>
        /// Convert CSV to XLSX (file to file).
        /// </summary>
		/// <remarks>
        /// Details: https://sautinsoft.com/products/excel/help/net/developer-guide/convert-csv-to-xlsx-in-csharp-vb.php
        /// </remarks>
        static void ConvertFromFile()
        {
            string inpFile = @"..\..\..\Example.csv";
            string outFile = @"..\..\..\Result.xlsx";

            ExcelDocument excelDocument = ExcelDocument.Load(inpFile, new LoadOptions { CsvTryParseNumbers = true });
            excelDocument.Save(outFile, new XlsxSaveOptions());

            // Important for Linux: Install MS Fonts
            // sudo apt install ttf-mscorefonts-installer -y

            // Open the result for demonstration purposes.
            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo(outFile) { UseShellExecute = true });
        }

        /// <summary>
        /// Convert CSV to XLSX (using Stream).
        /// </summary>
		/// <remarks>
        /// Details: https://sautinsoft.com/products/excel/help/net/developer-guide/convert-csv-to-xlsx-in-csharp-vb.php
        /// </remarks>
        static void ConvertFromStream()
        {

            // We need files only for demonstration purposes.
            // The conversion process will be done completely in memory.
            string inpFile = @"..\..\..\Example.csv";
            string outFile = @"..\..\..\ResultStream.xlsx";
            byte[] inpData = File.ReadAllBytes(inpFile);
            byte[] outData = null;

            using (MemoryStream msInp = new MemoryStream(inpData))
            {

                // Load a document.
                ExcelDocument excelDocument = ExcelDocument.Load(inpFile, new LoadOptions { CsvTryParseNumbers = true });

                // Save the excel document to XLSX format.
                using (MemoryStream outMs = new MemoryStream())
                {
                    excelDocument.Save(outMs, new XlsxSaveOptions());
                    outData = outMs.ToArray();
                }
                // Show the result for demonstration purposes.
                if (outData != null)
                {
                    File.WriteAllBytes(outFile, outData);

                    // Important for Linux: Install MS Fonts
                    // sudo apt install ttf-mscorefonts-installer -y

                    System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo(outFile) { UseShellExecute = true });
                }
            }
        }
    }
}

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Imports SautinSoft.Excel
Imports System.IO

Namespace Example
	Friend Class Program
		Shared Sub Main(ByVal args() As String)
			' Get your free key here:   
			' https://sautinsoft.com/start-for-free/

			ConvertFromFile()
			ConvertFromStream()
		End Sub

		''' <summary>
		''' Convert CSV to XLSX (file to file).
		''' </summary>
		''' <remarks>
		''' Details: https://sautinsoft.com/products/excel/help/net/developer-guide/convert-csv-to-xlsx-in-csharp-vb.php
		''' </remarks>
		Private Shared Sub ConvertFromFile()
			Dim inpFile As String = "..\..\..\Example.csv"
			Dim outFile As String = "..\..\..\Result.xlsx"

			Dim excelDocument As ExcelDocument = ExcelDocument.Load(inpFile, New LoadOptions With {.CsvTryParseNumbers = True})
			excelDocument.Save(outFile, New XlsxSaveOptions())

			' Important for Linux: Install MS Fonts
			' sudo apt install ttf-mscorefonts-installer -y

			' Open the result for demonstration purposes.
			System.Diagnostics.Process.Start(New System.Diagnostics.ProcessStartInfo(outFile) With {.UseShellExecute = True})
		End Sub

		''' <summary>
		''' Convert CSV to XLSX (using Stream).
		''' </summary>
		''' <remarks>
		''' Details: https://sautinsoft.com/products/excel/help/net/developer-guide/convert-csv-to-xlsx-in-csharp-vb.php
		''' </remarks>
		Private Shared Sub ConvertFromStream()

			' We need files only for demonstration purposes.
			' The conversion process will be done completely in memory.
			Dim inpFile As String = "..\..\..\Example.csv"
			Dim outFile As String = "..\..\..\ResultStream.xlsx"
			Dim inpData() As Byte = File.ReadAllBytes(inpFile)
			Dim outData() As Byte = Nothing

			Using msInp As New MemoryStream(inpData)

				' Load a document.
				Dim excelDocument As ExcelDocument = ExcelDocument.Load(inpFile, New LoadOptions With {.CsvTryParseNumbers = True})

				' Save the excel document to XLSX format.
				Using outMs As New MemoryStream()
					excelDocument.Save(outMs, New XlsxSaveOptions())
					outData = outMs.ToArray()
				End Using
				' Show the result for demonstration purposes.
				If outData IsNot Nothing Then
					File.WriteAllBytes(outFile, outData)

					' Important for Linux: Install MS Fonts
					' sudo apt install ttf-mscorefonts-installer -y

					System.Diagnostics.Process.Start(New System.Diagnostics.ProcessStartInfo(outFile) With {.UseShellExecute = True})
				End If
			End Using
		End Sub
	End Class
End Namespace

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