--- title: How to use String.Format - and why you should care about it description: A tutorial on String.Format in C#, comparing it to concatenation and string interpolation, explaining positional placeholders, numeric and date formatting with... canonical: https://daily.dev/posts/how-to-use-string-format---and-why-you-should-care-about-it-zucpu8hdx twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: How to use String.Format - and why you should care about it | daily.dev og:description: A tutorial on String.Format in C#, comparing it to concatenation and string interpolation, explaining positional placeholders, numeric and date formatting with... og:url: https://daily.dev/posts/how-to-use-string-format---and-why-you-should-care-about-it-zucpu8hdx og:image: https://api.daily.dev/og/posts/zucPu8HdX.png og:image:alt: How to use String.Format - and why you should care about it og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # How to use String.Format - and why you should care about it **[Code4IT](https://daily.dev/sources/code4it)** · 9 min read · 0 upvotes · 0 comments ## Summary A tutorial on String.Format in C#, comparing it to concatenation and string interpolation, explaining positional placeholders, numeric and date formatting with standard format strings, culture-specific formatting, and how to build a custom formatter by implementing IFormatProvider and ICustomFormatter interfaces using a CapturedPokemon example class. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How do I create a custom formatter for a class using String.Format in C#? Implement both IFormatProvider and ICustomFormatter on a class. IFormatProvider's GetFormat method returns 'this' when asked for ICustomFormatter; the ICustomFormatter.Format method receives the format string, the target object, and the format provider, and returns the formatted string based on a switch over the format string (e.g., 'full', 'pokedex', 'name'). Pass an instance of this formatter as the first argument to String.Format. _daily.dev surfaces more C# formatting patterns for developers building custom IFormatProvider implementations._ ### What happens if String.Format has more placeholders than arguments in C#? A FormatException is thrown with the message that the zero-based index must be greater than or equal to zero and less than the size of the argument list. Conversely, if there are more arguments than placeholders, the extra arguments are simply ignored and no exception occurs. _developers debugging String.Format exceptions in C# can find related gotchas on daily.dev._ --- Tags: [#.net](https://daily.dev/tags/.net), [#c#](https://daily.dev/tags/c#) [View this post on daily.dev](https://daily.dev/posts/how-to-use-string-format---and-why-you-should-care-about-it-zucpu8hdx) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"How to use String.Format - and why you should care about it","url":"https://daily.dev/posts/how-to-use-string-format---and-why-you-should-care-about-it-zucpu8hdx","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/how-to-use-string-format---and-why-you-should-care-about-it-zucpu8hdx"},"datePublished":"2026-10-04T13:05:40.359Z","dateModified":"2026-10-04T13:11:15.638Z","description":"A tutorial on String.Format in C#, comparing it to concatenation and string interpolation, explaining positional placeholders, numeric and date formatting with...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/dfbe7c03cea8d54915c957a38180da1f?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/dfbe7c03cea8d54915c957a38180da1f?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Code4IT","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Code4IT","logo":"https://media.daily.dev/image/upload/s--OaaG4G10--/f_auto,q_auto/v1791119049/logos/code4it?_a=BAMAMicg0","url":"https://daily.dev/sources/code4it"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/how-to-use-string-format---and-why-you-should-care-about-it-zucpu8hdx","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":".net,c#","timeRequired":"PT9M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Code4IT","item":"https://daily.dev/sources/code4it"},{"@type":"ListItem","position":3,"name":"How to use String.Format - and why you should care about it"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/how-to-use-string-format---and-why-you-should-care-about-it-zucpu8hdx#faq","mainEntity":[{"@type":"Question","name":"How do I create a custom formatter for a class using String.Format in C#?","acceptedAnswer":{"@type":"Answer","text":"Implement both IFormatProvider and ICustomFormatter on a class. 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