How to Load Existing Spreadsheets in C#

Which File Formats Can I Load?

:path=/static-assets/excel/content-code-examples/how-to/load-spreadsheet-load-spreadsheet.cs

using IronXL;

// Supported for XLSX, XLS, XLSM, XLTX, CSV and TSV
WorkBook workBook = WorkBook.Load("sample.xlsx");

Imports IronXL

' Supported for XLSX, XLS, XLSM, XLTX, CSV and TSV
Private workBook As WorkBook = WorkBook.Load("sample.xlsx")

The flexibility to load multiple file formats means you can work with legacy Excel files (XLS), modern Excel workbooks (XLSX), macro-enabled workbooks (XLSM), and template files (XLTX). This compatibility ensures smooth migration from older systems while supporting modern Excel features. For more details on creating new spreadsheets, check out our comprehensive guide.

How Do I Handle Password-Protected Files?

Working with sensitive data often requires password protection. IronXL makes it simple to load password-protected workbooks by providing the password as a parameter:

// Load password-protected Excel file
WorkBook protectedWorkBook = WorkBook.Load("protected.xlsx", "myPassword123");

// Work with the workbook normally
WorkSheet sheet = protectedWorkBook.DefaultWorkSheet;
sheet["B2"].Value = "Updated secure data";

// Save with password protection
protectedWorkBook.SaveAs("updated_protected.xlsx");

// Load password-protected Excel file
WorkBook protectedWorkBook = WorkBook.Load("protected.xlsx", "myPassword123");

// Work with the workbook normally
WorkSheet sheet = protectedWorkBook.DefaultWorkSheet;
sheet["B2"].Value = "Updated secure data";

// Save with password protection
protectedWorkBook.SaveAs("updated_protected.xlsx");

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What About Loading from Byte Arrays or Streams?

In modern applications, files often come from various sources like web uploads, API responses, or database BLOBs. IronXL handles these scenarios elegantly:

// Loading from byte array
byte[] excelBytes = File.ReadAllBytes("sample.xlsx");
WorkBook workBookFromBytes = WorkBook.FromByteArray(excelBytes);

// Loading from stream
using (FileStream stream = new FileStream("sample.xlsx", FileMode.Open))
{
    WorkBook workBookFromStream = WorkBook.FromStream(stream);

    // Process the workbook
    var sheet = workBookFromStream.DefaultWorkSheet;
    Console.WriteLine($"Sheet has {sheet.RowCount} rows");
}

// Loading from MemoryStream (common in web applications)
using (MemoryStream memStream = new MemoryStream(excelBytes))
{
    WorkBook workBookFromMemory = WorkBook.FromStream(memStream);
}

// Loading from byte array
byte[] excelBytes = File.ReadAllBytes("sample.xlsx");
WorkBook workBookFromBytes = WorkBook.FromByteArray(excelBytes);

// Loading from stream
using (FileStream stream = new FileStream("sample.xlsx", FileMode.Open))
{
    WorkBook workBookFromStream = WorkBook.FromStream(stream);

    // Process the workbook
    var sheet = workBookFromStream.DefaultWorkSheet;
    Console.WriteLine($"Sheet has {sheet.RowCount} rows");
}

// Loading from MemoryStream (common in web applications)
using (MemoryStream memStream = new MemoryStream(excelBytes))
{
    WorkBook workBookFromMemory = WorkBook.FromStream(memStream);
}

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When Is LoadCSV Better Than Load?

The LoadCSV method provides enhanced control over CSV parsing, making it ideal when you need to specify custom delimiters, handle different encodings, or work with large CSV files. It's particularly useful when dealing with international data formats or when CSV files use non-standard delimiters like semicolons or pipes.

How Does LoadCSV Handle Special Characters?

:path=/static-assets/excel/content-code-examples/how-to/load-spreadsheet-load-csv.cs

using IronXL;

// Load CSV file
WorkBook workBook = WorkBook.LoadCSV("sample.csv");

Imports IronXL

' Load CSV file
Private workBook As WorkBook = WorkBook.LoadCSV("sample.csv")

The LoadCSV method automatically handles various encodings including UTF-8, UTF-16, and ASCII, ensuring that special characters, accented letters, and international symbols are preserved correctly. This is crucial when working with multilingual data or scientific notation. Learn more about writing CSV files in .NET for complete CSV workflow management.

Why Would I Convert DataSet to Excel?

Converting DataSet objects to Excel format is essential for reporting, data export, and creating user-friendly data presentations. Business users often prefer Excel formats for data analysis, and automated reports frequently need to transform database results into spreadsheet formats. This conversion enables features like conditional formatting, chart creation, and formula application that aren't available in raw DataSet objects.

What Happens to DataSet Relationships in Excel?

When loading a DataSet with multiple related tables, IronXL creates separate worksheets for each DataTable in the DataSet. Table relationships are preserved through consistent key values, allowing users to maintain data integrity when working with the exported Excel file. This makes it ideal for exporting complex database schemas while maintaining referential integrity.

Can I Load Multiple Tables from DataSet?

:path=/static-assets/excel/content-code-examples/how-to/load-spreadsheet-load-dataset.cs

using IronXL;
using System.Data;

// Create dataset
DataSet dataSet = new DataSet();

// Create workbook
WorkBook workBook = WorkBook.Create();

// Load DataSet
WorkBook.LoadWorkSheetsFromDataSet(dataSet, workBook);

Imports IronXL
Imports System.Data

' Create dataset
Private dataSet As New DataSet()

' Create workbook
Private workBook As WorkBook = WorkBook.Create()

' Load DataSet
WorkBook.LoadWorkSheetsFromDataSet(dataSet, workBook)

For more advanced scenarios involving database integration, explore our guide on Excel to SQL via System.Data.DataSet which demonstrates bidirectional data flow between Excel and databases.

The ability to load various data sources into Excel format makes IronXL an invaluable tool for .NET developers. Whether you're building reporting systems, data migration tools, or business intelligence applications, the loading capabilities provide the foundation for powerful spreadsheet manipulation. For more examples and advanced techniques, visit our comprehensive tutorials section.