for-loop

C# – Remove items from a list while iterating

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There are two ways to iterate through a List<T> and remove items based on a condition: These remove items from the list in an in-place manner (i.e. modify the original list) and avoid the problems you run into when doing this incorrectly (such as using a foreach or looping forward). I’ll show examples below. Then … Read more

C# – Serialize and deserialize a multidimensional array to JSON

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System.Text.Json doesn’t support serializing / deserializing multidimensional arrays. When you try, it throws an exception like this – System.NotSupportedException: The type ‘System.Int[,] is not supported. You have three options: In this article, I’ll show an example of how to create a custom JsonConverter that handles multidimensional arrays. In this example, I’ll specifically show how to … Read more

C# – How to change StreamWriter’s buffer size

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StreamWriter buffers by writing data to an internal char array with a default size of 1024 (and a minimum size of 128). Once the buffer is full (or when you dispose the StreamWriter), it flushes the buffer to the underlying stream. You can change StreamWriter’s buffer size by passing in the bufferSize parameter. Here’s an … Read more

C# – How to disable ModelStateInvalidFilter

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There are two options for disabling ModelStateInvalidFilter: You’d do this when you want to manually perform model validation. I’ll show both options below. Disable ModelStateInvalidFilter globally To disable ModelStateInvalidFilter for *all* actions, set SuppressModelStateInvalidFilter=true in ConfigureApiBehaviorOptions, like this: Disable ModelStateInvalidFilter for specific actions To disable ModelStateInvalidFilter selectively, you can implement an IActionModelConvention attribute that removes … Read more

C# – The performance gains of HttpClient reusing connections

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When you use the same instance of HttpClient for multiple requests (sequential and concurrent) to the same URL, it’ll reuse connections. Requests that get to reuse a connection are 5.5-8.5x faster than requests that have to open a new connection. There are a few scenarios that benefit from this connection reuse: Measuring the performance gains … Read more

C# – Use yield return to minimize memory usage

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Let’s say you want to search for specific characters in a large text file and return a list of context objects to the calling code for further processing (such as showing the results in the UI). One way to do that is to build the entire list at once and return it. If you don’t … Read more

C# – Add or overwrite a value in ConcurrentDictionary

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The simplest way to add or overwrite a value in a ConcurrentDictionary is to use the indexer: If the key doesn’t exist, this adds it. If the key exists, this overwrites it. The indexer is thread-safe. The indexer is the simplest way to unconditionally add / overwrite a value. Sometimes you’ll want to use other … Read more

C# – Pad a 2D array on all sides

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Padding a 2D array on all sides means adding new rows on the top and bottom, new columns on the left and right, and then copying the original elements to the center of the padded array. It looks like this: There are two approaches for copying the elements. You can either copy individual items in … Read more

Logging to the database with ASP.NET Core

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I was reading about logging in ASP.NET when I came across this statement about logging to the database: When logging to SQL Server, don’t do so directly. Instead, add log messages to an in-memory queue and have a background worker dequeue and insert data to SQL Server. Paraphrased from Microsoft – No asynchronous logger methods … Read more

Algorithm Explained: Sum two big integers the hard way

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Problem statement: Sum two big integers that are passed in as strings. Return the sum as a string. In other words, implement the following method: Constraint: Don’t use the built-in BigInteger class (note: this is the name in C# and may have a different name in other languages). Do it the hard way instead. If … Read more

Collection was modified; enumeration operation may not execute

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If you try to add/remove items from a collection while it’s being looped over in a foreach loop (enumerated), then you’ll get the following exception: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.at System.Collections.Generic.List`1.Enumerator.MoveNext() This error can happen in two scenarios: The solution to this problem depends on which scenario you’re in. In this … Read more

NLog – Log to console

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There are two configuration options for logging to the console when you’re using NLog: In this article, I’ll show how to configure these two targets using nlog.config. At the end, I’ll show an example of configuring NLog programmatically. Console target Add a Console target and a rule that writes to that target in nlog.config, like … Read more

WinForms – How to remove checked items from CheckedListBox

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Normally the items in a CheckedListBox are hardcoded or added programmatically (from an enum or from binding a data source). But sometimes you may want to allow the user to add and remove items from a CheckedListItem. In this article I’ll show how to add items and remove them. I’ll be working with text, and … Read more

HackerRank – Two Strings solution

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In this article, I’ll explain how to solve the Two Strings algorithm problem on HackerRank. Problem statement: Given two strings, determine if they have a substring in common. The strings can have up to 100k characters. Example: Given “hello world” and “world”, do they have a substring in common? Yes, they many substrings in common. … Read more

C# – SQL Bulk Insert with SqlBulkCopy

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When you need to insert multiple rows into the database, consider doing a Bulk Insert instead of inserting one row at a time. Bulk Insertions are up to 20x faster than executing SQL Insert repeatedly. The simplest way to do a SQL Bulk Insert is by using the built-in SqlBulkCopy (from System.Data.SqlClient) with a DataTable. … Read more

WinForms – How to programmatically check items in CheckedListBox

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A CheckedListBox allows the user to check one or more checkboxes. Sometimes you’ll want to be able to check the boxes programmatically. For example, you may want to allow the user to check or uncheck all boxes at once. Or perhaps you want to persist the values the user checked and load them later. To … Read more

C# – ManualResetEventSlim and AutoResetEvent

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When you want thread(s) to wait until they’re signaled before continuing, there are two simple options: I’ll show examples of using both of these. ManualResetEventSlim examples ManualResetEventSlim is like waving a flag at a car race. All race cars (threads) line up at the starting line and wait for the flag, and then they all … Read more

C# – Reuse JsonSerializerOptions for performance

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Reusing JsonSerializerOptions (from System.Text.Json) is optimal for performance. It caches type info, which results in a 200x speedup when it deals with the type again. Therefore, always try to reuse JsonSerializerOptions. I’ll show a speed comparison of serializing with and without reusing JsonSerializerOptions. Measuring the performance gains of reusing JsonSerializerOptions To measure the performance gains … Read more

C# – Hex string to byte array

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This article shows code for converting a hex string to a byte array, unit tests, and a speed comparison. First, this diagram shows the algorithm for converting a hex string to a byte array. To convert a hex string to a byte array, you need to loop through the hex string and convert two characters … Read more

C# – How to make concurrent requests with HttpClient

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The HttpClient class was designed to be used concurrently. It’s thread-safe and can handle multiple requests. You can fire off multiple requests from the same thread and await all of the responses, or fire off requests from multiple threads. No matter what the scenario, HttpClient was built to handle concurrent requests. To use HttpClient effectively … Read more

C# – Use SemaphoreSlim for throttling threads

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When you have multiple threads trying to do work at the same time, and you want to throttle how many of them are actually executing (such as when you’re sending concurrent requests with HttpClient), you can use SemaphoreSlim. Example – a busy grocery store Grocery stores have a limited number of checkout lanes open. Let’s … Read more

C# – Pass in a Func to override behavior

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If I want to change the behavior of a method from the outside, I can pass in a function pointer. This approach exists in every language, and is one way to implement the Strategy Pattern. In C#, function pointers are referred to as delegates, and the two most common ones are Action and Func. The … Read more

Refactoring the Large Class code smell

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The Large Class code smells refers to a class that has too many responsibilities. It’s doing too much. Ideally a class should only have one responsibility (Single Responsibility Principle). Code Smell: Large Class Definition: A class has too many responsibilities. Solution: Large Class code smell example Here’s an example of the Large Class code smell … Read more