# CFStringGetDoubleValue(_:) Returns the primary `double` value represented by a string. ``` func CFStringGetDoubleValue(_ str: CFString!) -> Double ``` ## Parameters `str` A string that represents a double value. The only allowed characters are the ASCII digit characters (ASCII `0x30` - `0x39`), the plus sign (ASCII `0x2B`), the minus sign (ASCII `0x2D`), and the period character (ASCII `0x2E`). ## Return Value The `double` value represented by `str`, or `0.0` if there is a scanning error (if the string contains disallowed characters or does not represent a double value). ## Discussion Consider the following example: ```objc double val = CFStringGetDoubleValue(CFSTR("0.123")); ``` The variable `val` in this example would contain the value `0.123` after the function is called. --- 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)