如何从字符数组中获取UnsafeMutableBufferPointer

Question

let array : [Character] = ....
func getUnsafeMP(array: [Character]) -> UnsafeMutableBufferPointer<Character> {

    let count = array.count
    let memory = UnsafeMutablePointer<Character>(allocatingCapacity: count)

    for (index , value) in array.enumerated() {

        memory[index] = value //it fails here EXC_BAD_ACCESS
    }

    let buffer = UnsafeMutableBufferPointer(start: memory, count: count)

    return buffer
}

Answer 1

由unsafeMutablePointer寻址的内存可以处于以下三种状态之一：

/// - Memory is not allocated (for example, pointer is null, or memory has
///   been deallocated previously).
///
/// - Memory is allocated, but value has not been initialized.
///
/// - Memory is allocated and value is initialised.

呼叫

let memory = UnsafeMutablePointer<Character>(allocatingCapacity: count)

分配内存，但不初始化内存：

/// Allocate and point at uninitialized aligned memory for `count`
/// instances of `Pointee`.
///
/// - Postcondition: The pointee is allocated, but not initialized.
public init(allocatingCapacity count: Int)

/// Access the pointee at `self + i`.
///
/// - Precondition: the pointee at `self + i` is initialized.
public subscript(i: Int) -> Pointee { get nonmutating set }

memory.initializeFrom(array)

当然，您最终必须取消初始化并释放内存。

另一种方法是

var cArray: [Character] = ["A", "B", "C"]
cArray.withUnsafeMutableBufferPointer { bufPtr  in
    // ...
}

这里没有分配新的内存，但是使用指向数组连续存储的指针调用闭包。此缓冲区指针仅在闭包内部有效。