# CFMutableString ``` class CFMutableString ``` ## Overview CFMutableString manages dynamic strings. The basic interface for managing strings is provided by [`CFString`](/documentation/CoreFoundation/CFString). CFMutableString adds functions to modify the contents of a string. CFMutableString is “toll-free bridged” with its Cocoa Foundation counterpart, . This means that the Core Foundation type is interchangeable in function or method calls with the bridged Foundation object. Therefore, in a method where you see an `NSMutableString *` parameter, you can pass in a `CFMutableStringRef`, and in a function where you see a `CFMutableStringRef` parameter, you can pass in an NSMutableString instance. This also applies to concrete subclasses of NSMutableString. See [Toll-Free Bridged Types](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFDesignConcepts/Articles/tollFreeBridgedTypes.html#//apple_ref/doc/uid/TP40010677) for more information on toll-free bridging. ## Topics ### CFMutableString Miscellaneous Functions [`CFStringAppend(_:_:)`](/documentation/CoreFoundation/CFStringAppend(_:_:)) Appends the characters of a string to those of a CFMutableString object. [`CFStringAppendCharacters(_:_:_:)`](/documentation/CoreFoundation/CFStringAppendCharacters(_:_:_:)) Appends a buffer of Unicode characters to the character contents of a CFMutableString object. [`CFStringAppendCString(_:_:_:)`](/documentation/CoreFoundation/CFStringAppendCString(_:_:_:)) Appends a C string to the character contents of a CFMutableString object. [`CFStringAppendFormat`](/documentation/CoreFoundation/CFStringAppendFormat) Appends a formatted string to the character contents of a CFMutableString object. [`CFStringAppendFormatAndArguments(_:_:_:_:)`](/documentation/CoreFoundation/CFStringAppendFormatAndArguments(_:_:_:_:)) Appends a formatted string to the character contents of a CFMutableString object. [`CFStringAppendPascalString(_:_:_:)`](/documentation/CoreFoundation/CFStringAppendPascalString(_:_:_:)) Appends a Pascal string to the character contents of a CFMutableString object. [`CFStringCapitalize(_:_:)`](/documentation/CoreFoundation/CFStringCapitalize(_:_:)) Changes the first character in each word of a string to uppercase (if it is a lowercase alphabetical character). [`CFStringCreateMutable(_:_:)`](/documentation/CoreFoundation/CFStringCreateMutable(_:_:)) Creates an empty CFMutableString object. [`CFStringCreateMutableCopy(_:_:_:)`](/documentation/CoreFoundation/CFStringCreateMutableCopy(_:_:_:)) Creates a mutable copy of a string. [`CFStringCreateMutableWithExternalCharactersNoCopy(_:_:_:_:_:)`](/documentation/CoreFoundation/CFStringCreateMutableWithExternalCharactersNoCopy(_:_:_:_:_:)) Creates a CFMutableString object whose Unicode character buffer is controlled externally. [`CFStringDelete(_:_:)`](/documentation/CoreFoundation/CFStringDelete(_:_:)) Deletes a range of characters in a string. [`CFStringFindAndReplace(_:_:_:_:_:)`](/documentation/CoreFoundation/CFStringFindAndReplace(_:_:_:_:_:)) Replaces all occurrences of a substring within a given range. [`CFStringFold(_:_:_:)`](/documentation/CoreFoundation/CFStringFold(_:_:_:)) Folds a given string into the form specified by optional flags. [`CFStringInsert(_:_:_:)`](/documentation/CoreFoundation/CFStringInsert(_:_:_:)) Inserts a string at a specified location in the character buffer of a CFMutableString object. [`CFStringLowercase(_:_:)`](/documentation/CoreFoundation/CFStringLowercase(_:_:)) Changes all uppercase alphabetical characters in a CFMutableString to lowercase. [`CFStringNormalize(_:_:)`](/documentation/CoreFoundation/CFStringNormalize(_:_:)) Normalizes the string into the specified form as described in Unicode Technical Report #15. [`CFStringPad(_:_:_:_:)`](/documentation/CoreFoundation/CFStringPad(_:_:_:_:)) Enlarges a string, padding it with specified characters, or truncates the string. [`CFStringReplace(_:_:_:)`](/documentation/CoreFoundation/CFStringReplace(_:_:_:)) Replaces part of the character contents of a CFMutableString object with another string. [`CFStringReplaceAll(_:_:)`](/documentation/CoreFoundation/CFStringReplaceAll(_:_:)) Replaces all characters of a CFMutableString object with other characters. [`CFStringSetExternalCharactersNoCopy(_:_:_:_:)`](/documentation/CoreFoundation/CFStringSetExternalCharactersNoCopy(_:_:_:_:)) Notifies a CFMutableString object that its external backing store of Unicode characters has changed. [`CFStringTransform(_:_:_:_:)`](/documentation/CoreFoundation/CFStringTransform(_:_:_:_:)) Perform in-place transliteration on a mutable string. [`CFStringTrim(_:_:)`](/documentation/CoreFoundation/CFStringTrim(_:_:)) Trims a specified substring from the beginning and end of a CFMutableString object. [`CFStringTrimWhitespace(_:)`](/documentation/CoreFoundation/CFStringTrimWhitespace(_:)) Trims whitespace from the beginning and end of a CFMutableString object. [`CFStringUppercase(_:_:)`](/documentation/CoreFoundation/CFStringUppercase(_:_:)) Changes all lowercase alphabetical characters in a CFMutableString object to uppercase. ### Constants [`CFStringNormalizationForm`](/documentation/CoreFoundation/CFStringNormalizationForm) Unicode normalization forms as described in Unicode Technical Report #15. [Transform Identifiers for CFStringTransform](/documentation/CoreFoundation/transform-identifiers-for-cfstringtransform) Constants that identify transforms used with [`CFStringTransform(_:_:_:_:)`](/documentation/CoreFoundation/CFStringTransform(_:_:_:_:)). ## See Also [Property List Programming Topics for Core Foundation](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFPropertyLists/CFPropertyLists.html#//apple_ref/doc/uid/10000130i) [String Programming Guide for Core Foundation](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFStrings/introCFStrings.html#//apple_ref/doc/uid/10000131i) --- 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)