# init(format:locale:arguments:) Returns an `NSString` object initialized by using a given format string as a template into which the remaining argument values are substituted according to given locale information. This method is meant to be called from within a variadic function, where the argument list will be available. ``` convenience init(format: String, locale: Any?, arguments argList: CVaListPointer) ``` ## Parameters `format` A format string. See [Formatting String Objects](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Strings/Articles/FormatStrings.html#//apple_ref/doc/uid/20000943) for examples of how to use this method, and [String Format Specifiers](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFStrings/formatSpecifiers.html#//apple_ref/doc/uid/TP40004265) for a list of format specifiers. This value must not be `nil`. > Important: > Raises an `NSInvalidArgumentException` if `format` is `nil`. `locale` An [`NSLocale`](/documentation/Foundation/NSLocale) object specifying the locale to use. To use the current locale (specified by user preferences), pass [[`NSLocale`](/documentation/Foundation/NSLocale) [`current`](/documentation/Foundation/NSLocale/current)]. To use the system locale, pass `nil`. For legacy support, this may be an instance of `NSDictionary` containing locale information. `argList` A list of arguments to substitute into `format`. ## Return Value An `NSString` object initialized by using `format` as a template into which values in `argList` are substituted according the locale information in `locale`. The returned object may be different from the original receiver. ## Discussion The following Objective-C code fragment illustrates how to create a string from `myArgs`, which is derived from a string object with the value “Cost:” and an int with the value 32: ```objc va_list myArgs; NSString *myString = [[NSString alloc] initWithFormat:@"%@: %d\n" locale:[NSLocale currentLocale] arguments:myArgs]; ``` The resulting string has the value “`Cost: 32\n`”. See [String Programming Guide](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Strings/introStrings.html#//apple_ref/doc/uid/10000035i) for more information. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)