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# CFStringCreateWithSubstring(_:_:_:)

Creates an immutable string from a segment (substring) of an existing string.

```
func CFStringCreateWithSubstring(_ alloc: CFAllocator!, _ str: CFString!, _ range: CFRange) -> CFString!
```

## Parameters

`alloc`

The allocator to use to allocate memory for the new string. Pass `NULL` or [`kCFAllocatorDefault`](/documentation/CoreFoundation/kCFAllocatorDefault) to use the current default allocator.

`str`

The string from which to create the new string.

`range`

The range of characters in `str` to copy. The specified range must not exceed the length of the string.

## Return Value

An immutable string, or `NULL` if there was a problem creating the object. Ownership follows the [The Create Rule](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/Ownership.html#//apple_ref/doc/uid/20001148-103029).

## Discussion

---

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