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How to Handle QR Code Error Messages in C#

Curtis Chau
Curtis Chau
Updated:

IronQR's error handling helps you catch read and write failures, log diagnostics, and get clear results from every scan. If you do not add explicit checks, both an empty result and a corrupted file will return nothing, so you will not know what went wrong. By adding targeted exception handling and diagnostic logging, you can turn silent failures into useful feedback. This guide explains how to handle empty results, manage write-time exceptions, and build a structured logging wrapper for batch processing.

Quickstart: Handle QR Code Errors

Wrap QR read operations in a try-catch block and log diagnostics for file and decode failures.

  1. Install IronQR with NuGet Package Manager

    PM > Install-Package IronQR

  2. Copy and run this code snippet.

    using IronQr;
using IronSoftware.Drawing;

try
{
    var input = new QrImageInput(AnyBitmap.FromFile("label.png"));
    var results = new QrReader().Read(input);
    Console.WriteLine($"Found {results.Count()} QR code(s)");
}
catch (IOException ex)
{
    Console.Error.WriteLine($"File error: {ex.Message}");
}

  3. Deploy to test on your live environment

    Start using IronQR in your project today with a free trial

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Minimal Workflow (5 steps)

  1. Download the IronQR C# library for QR code error handling
  2. Wrap QR read/write calls in try-catch blocks
  3. Catch IOException and ArgumentException for specific failures
  4. Log diagnostics for empty results and exceptions
  5. Use structured JSON logging for pipeline observability

Handling Read Errors and Empty Results

Without logging, an empty result and a corrupted file appear identical to the caller. The following example detects file access failures and issues a warning if the scan returns no results.

Input

This QR example input exists on disk. We will simulate both scenarios: one where the user retrieves and decodes the file, and another where the file path is incorrect.

Valid QR code input encoding https://ironsoftware.com/qr/scan-1 
:path=/static-assets/qr/content-code-examples/how-to/detailed-error-messages/read-diagnostics.cs
using IronQr;
using IronSoftware.Drawing;

string filePath = "damaged-scan.png";

try
{
    // File-level failure throws IOException or FileNotFoundException
    var inputBmp = AnyBitmap.FromFile(filePath);
    var imageInput = new QrImageInput(inputBmp);

    var reader = new QrReader();
    IEnumerable<QrResult> results = reader.Read(imageInput);

    if (!results.Any())
    {
        // Not an exception — but a diagnostic event worth logging
        Console.Error.WriteLine($"[WARN] No QR codes found in: {filePath}");
        Console.Error.WriteLine($"  Action: Verify image quality or try a different scan");
    }
    else
    {
        foreach (QrResult result in results)
        {
            Console.WriteLine($"[{result.QrType}] {result.Value}");
        }
    }
}
catch (FileNotFoundException)
{
    Console.Error.WriteLine($"[ERROR] File not found: {filePath}");
}
catch (IOException ex)
{
    Console.Error.WriteLine($"[ERROR] Cannot read file: {filePath} — {ex.Message}");
}
catch (Exception ex)
{
    Console.Error.WriteLine($"[ERROR] Unexpected failure reading {filePath}: {ex.GetType().Name} — {ex.Message}");
}

Imports IronQr
Imports IronSoftware.Drawing

Module Module1
    Sub Main()
        Dim filePath As String = "damaged-scan.png"

        Try
            ' File-level failure throws IOException or FileNotFoundException
            Dim inputBmp = AnyBitmap.FromFile(filePath)
            Dim imageInput = New QrImageInput(inputBmp)

            Dim reader = New QrReader()
            Dim results As IEnumerable(Of QrResult) = reader.Read(imageInput)

            If Not results.Any() Then
                ' Not an exception — but a diagnostic event worth logging
                Console.Error.WriteLine($"[WARN] No QR codes found in: {filePath}")
                Console.Error.WriteLine("  Action: Verify image quality or try a different scan")
            Else
                For Each result As QrResult In results
                    Console.WriteLine($"[{result.QrType}] {result.Value}")
                Next
            End If
        Catch ex As FileNotFoundException
            Console.Error.WriteLine($"[ERROR] File not found: {filePath}")
        Catch ex As IOException
            Console.Error.WriteLine($"[ERROR] Cannot read file: {filePath} — {ex.Message}")
        Catch ex As Exception
            Console.Error.WriteLine($"[ERROR] Unexpected failure reading {filePath}: {ex.GetType().Name} — {ex.Message}")
        End Try
    End Sub
End Module
$vbLabelText   $csharpLabel

Output

Terminal output showing [QRCode] https://ironsoftware.com/qr/scan-1 for a successful QR code read

Please noteA success read would just return the QR code value, while an error during the runtime would show the exception message or warnings shown below.

The console below shows a [WARN] for the empty-result case and an [ERROR] for the missing file, with the file path and a suggested action for each.

Terminal output showing WARN for no QR codes found in damaged-scan.png and ERROR file not found for missing-label.png

Handling Write Failures

Passing null to QrWriter.Write triggers an IronQrEncodingException. Data that exceeds capacity for the configured error correction level also throws, since higher correction levels reduce available data capacity.

Input

The two input variables below define the failure scenarios: nullContent is null and oversizedContent is a 5,000-character string that exceeds QR capacity at the highest correction level.

:path=/static-assets/qr/content-code-examples/how-to/detailed-error-messages/write-diagnostics.cs
using IronQr;

string? content = null; // null throws IronQrEncodingException 
string oversizedContent = new string('A', 5000); // 5,000 chars exceeds QR capacity at Highest error correction level 

// Scenario 1: null input
try
{   
    QrCode qr = QrWriter.Write(content); // Input
}
catch (Exception ex)
{
    Console.Error.WriteLine($"[ERROR] Null content: {ex.GetType().Name} — {ex.Message}"); // Output
}

// Scenario 2: data exceeds QR capacity at the configured error correction level
try
{
    var options = new QrOptions(QrErrorCorrectionLevel.Highest);
    QrCode qr = QrWriter.Write(oversizedContent, options); // Input
}
catch (Exception ex)
{
    Console.Error.WriteLine($"[ERROR] QR capacity exceeded: {ex.Message}"); // Output
    Console.Error.WriteLine($"  Input length: {oversizedContent.Length} chars");
    Console.Error.WriteLine($"  Action: Reduce content or lower error correction level");
}

Imports IronQr

Dim content As String = Nothing ' Nothing throws IronQrEncodingException 
Dim oversizedContent As String = New String("A"c, 5000) ' 5,000 chars exceeds QR capacity at Highest error correction level 

' Scenario 1: null input
Try
    Dim qr As QrCode = QrWriter.Write(content) ' Input
Catch ex As Exception
    Console.Error.WriteLine($"[ERROR] Null content: {ex.GetType().Name} — {ex.Message}") ' Output
End Try

' Scenario 2: data exceeds QR capacity at the configured error correction level
Try
    Dim options As New QrOptions(QrErrorCorrectionLevel.Highest)
    Dim qr As QrCode = QrWriter.Write(oversizedContent, options) ' Input
Catch ex As Exception
    Console.Error.WriteLine($"[ERROR] QR capacity exceeded: {ex.Message}") ' Output
    Console.Error.WriteLine($"  Input length: {oversizedContent.Length} chars")
    Console.Error.WriteLine("  Action: Reduce content or lower error correction level")
End Try
$vbLabelText   $csharpLabel

Output

The console shows the exception type and message for both failure scenarios.

Terminal output showing IronQrEncodingException for null content passed to QrWriter.Write

Log the input length with the exception message to identify whether the issue requires shorter content or a lower correction level. For user input, validate string length and check for null values before encoding to reduce exception overhead and improve diagnostics.

Logging QR Code Operations

Use IronSoftware.Logger to capture internal diagnostics. For each read operation, implement a helper that logs the file path, result count, and elapsed time as JSON to ensure clear output for the entire batch.

Input

The batch includes four valid QR code images from qr-scans/ and a fifth file, scan-05-broken.png, with invalid bytes.

QR code encoding https://ironsoftware.com/qr/scan-1

Scan 1

QR code encoding https://ironsoftware.com/qr/scan-2

Scan 2

QR code encoding https://ironsoftware.com/qr/scan-3

Scan 3

QR code encoding https://ironsoftware.com/qr/scan-4

Scan 4 

:path=/static-assets/qr/content-code-examples/how-to/detailed-error-messages/logging-wrapper.cs
using IronQr;
using IronSoftware.Drawing;
using System.Diagnostics;

// Enable shared Iron Software logging for internal diagnostics
IronSoftware.Logger.LoggingMode = IronSoftware.Logger.LoggingModes.All;
IronSoftware.Logger.LogFilePath = "ironqr-debug.log";

// Reusable wrapper for structured observability
(IEnumerable<QrResult> Results, bool Success, string Error) ReadQrWithDiagnostics(string filePath)
{
    var sw = Stopwatch.StartNew();
    try
    {
        var input = new QrImageInput(AnyBitmap.FromFile(filePath));
        var results = new QrReader().Read(input).ToList();
        sw.Stop();

        Console.WriteLine($"{{\"op\":\"qr_read\",\"file\":\"{Path.GetFileName(filePath)}\","
            + $"\"status\":\"ok\",\"count\":{results.Count},\"ms\":{sw.ElapsedMilliseconds}}}");

        return (results, true, null);
    }
    catch (Exception ex)
    {
        sw.Stop();
        string error = $"{ex.GetType().Name}: {ex.Message}";

        Console.Error.WriteLine($"{{\"op\":\"qr_read\",\"file\":\"{Path.GetFileName(filePath)}\","
            + $"\"status\":\"error\",\"exception\":\"{ex.GetType().Name}\","
            + $"\"message\":\"{ex.Message}\",\"ms\":{sw.ElapsedMilliseconds}}}");

        return (Enumerable.Empty<QrResult>(), false, error);
    }
}

// Usage: process a batch with per-file isolation
string[] files = Directory.GetFiles("qr-scans/", "*.png");
int ok = 0, fail = 0;

foreach (string file in files)
{
    var (results, success, error) = ReadQrWithDiagnostics(file);
    if (success && results.Any()) ok++;
    else fail++;
}

Console.WriteLine($"\nBatch complete: {ok} success, {fail} failed/empty out of {files.Length} files");

Imports IronQr
Imports IronSoftware.Drawing
Imports System.Diagnostics
Imports System.IO
Imports System.Linq

' Enable shared Iron Software logging for internal diagnostics
IronSoftware.Logger.LoggingMode = IronSoftware.Logger.LoggingModes.All
IronSoftware.Logger.LogFilePath = "ironqr-debug.log"

' Reusable wrapper for structured observability
Private Function ReadQrWithDiagnostics(ByVal filePath As String) As (IEnumerable(Of QrResult), Boolean, String)
    Dim sw = Stopwatch.StartNew()
    Try
        Dim input = New QrImageInput(AnyBitmap.FromFile(filePath))
        Dim results = New QrReader().Read(input).ToList()
        sw.Stop()

        Console.WriteLine($"{{""op"":""qr_read"",""file"":""{Path.GetFileName(filePath)}"",""status"":""ok"",""count"":{results.Count},""ms"":{sw.ElapsedMilliseconds}}}")

        Return (results, True, Nothing)
    Catch ex As Exception
        sw.Stop()
        Dim error As String = $"{ex.GetType().Name}: {ex.Message}"

        Console.Error.WriteLine($"{{""op"":""qr_read"",""file"":""{Path.GetFileName(filePath)}"",""status"":""error"",""exception"":""{ex.GetType().Name}"",""message"":""{ex.Message}"",""ms"":{sw.ElapsedMilliseconds}}}")

        Return (Enumerable.Empty(Of QrResult)(), False, error)
    End Try
End Function

' Usage: process a batch with per-file isolation
Dim files As String() = Directory.GetFiles("qr-scans/", "*.png")
Dim ok As Integer = 0, fail As Integer = 0

For Each file As String In files
    Dim result = ReadQrWithDiagnostics(file)
    Dim results = result.Item1
    Dim success = result.Item2
    Dim error = result.Item3

    If success AndAlso results.Any() Then
        ok += 1
    Else
        fail += 1
    End If
Next

Console.WriteLine($"\nBatch complete: {ok} success, {fail} failed/empty out of {files.Length} files")
$vbLabelText   $csharpLabel

Output

The console shows JSON log lines for each file: four successful reads and one structured error entry for the broken file, followed by the batch summary. IronSoftware.Logger writes internal diagnostics to IronQR-debug.log at the same time. You can download the full debug log here.

Terminal output showing JSON structured log lines for 4 successful reads and 1 error, plus batch completion summary

The JSON output feeds directly into log aggregation tools: pipe stdout to Fluentd, Datadog, or CloudWatch in a containerized deployment. The ms field surfaces latency regressions, and the debug log captures internal processing steps that the wrapper does not.

Further Reading

View licensing options when you're ready for production.

Click here to download the complete DetailedErrorMessagesTest console app project.

Curtis Chau
Curtis Chau
  Chat with engineering team now
Technical Writer

Curtis Chau holds a Bachelor’s degree in Computer Science (Carleton University) and specializes in front-end development with expertise in Node.js, TypeScript, JavaScript, and React. Passionate about crafting intuitive and aesthetically pleasing user interfaces, Curtis enjoys working with modern frameworks and creating well-structured, visually appealing manuals.

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