# CTLineGetOffsetForStringIndex(_:_:_:) Determines the graphical offset or offsets for a string index. ``` func CTLineGetOffsetForStringIndex(_ line: CTLine, _ charIndex: CFIndex, _ secondaryOffset: UnsafeMutablePointer?) -> CGFloat ``` ## Parameters `line` The line from which the offset is requested. `charIndex` The string index corresponding to the desired position. `secondaryOffset` On output, the secondary offset along the baseline for `charIndex`. When a single caret is sufficient for a string index, this value will be the same as the primary offset, which is the return value of this function. May be `NULL`. ## Return Value The primary offset along the baseline for `charIndex`, or `0.0` if the line does not support string access. ## Discussion This function returns the graphical offset or offsets corresponding to a string index, suitable for movement between adjacent lines or for drawing a custom caret. For moving between adjacent lines, the primary offset can be adjusted for any relative indentation of the two lines; a constructed with the adjusted offset for its `x` value and `0.0` for its `y` value is suitable for passing to [`CTLineGetStringIndexForPosition(_:_:)`](/documentation/CoreText/CTLineGetStringIndexForPosition(_:_:)). For drawing a custom caret, the returned primary offset corresponds to the portion of the caret that represents the visual insertion location for a character whose direction matches the line’s writing direction. --- 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)