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[英]What does `UnsafeMutablePointer.initialize()`actually do?
[英]Thread 1: Fatal error: UnsafeMutablePointer.initialize overlapping range
我正在尝试使用
UnsafeMutablePointer<UnsafeMutablePointer<Float>?>!
因为它是我需要使用的方法的参数所必需的。 但是我不知道这是什么或如何使用。
我通过执行以下操作创建了此值:
var bytes2: [Float] = [39, 77, 111, 111, 102, 33, 39, 0]
let uint8Pointer2 = UnsafeMutablePointer<Float>.allocate(capacity: 8)
uint8Pointer2.initialize(from: &bytes2, count: 8)
var bytes: [Float] = [391, 771, 1111, 1111, 1012, 331, 319, 10]
var uint8Pointer = UnsafeMutablePointer<Float>?.init(uint8Pointer2)
uint8Pointer?.initialize(from: &bytes, count: 8)
let uint8Pointer1 = UnsafeMutablePointer<UnsafeMutablePointer<Float>?>!.init(&uint8Pointer)
uint8Pointer1?.initialize(from: &uint8Pointer, count: 8)
但是我得到了错误:
Thread 1: Fatal error: UnsafeMutablePointer.initialize overlapping range
我究竟做错了什么?
您正在制造不良行为。
var bytes2: [Float] = [39, 77, 111, 111, 102, 33, 39, 0]
let uint8Pointer2 = UnsafeMutablePointer<Float>.allocate(capacity: 8)
uint8Pointer2.initialize(from: &bytes2, count: 8)
创建一个指向某些内存的指针,并将该内存初始化为存储在bytes2
的值。
因此: uint8Pointer2 = [39, 77, 111, 111, 102, 33, 39, 0]
然后,您决定创建一个引用该指针的内存的指针:
var uint8Pointer = UnsafeMutablePointer<Float>?.init(uint8Pointer2)
因此,如果您打印uint8Pointer
,它将具有与uint8Pointer2
完全相同的值。如果您决定也更改其任何值,它也会更改uint8Pointer2
的值。
因此,当您这样做时:
var bytes: [Float] = [391, 771, 1111, 1111, 1012, 331, 319, 10]
uint8Pointer?.initialize(from: &bytes, count: 8)
它用[391, 771, 1111, 1111, 1012, 331, 319, 10]
uint8Pointer2
覆盖了uint8Pointer2
的值。
到目前为止, uint8Pointer
是只是一个浅拷贝uint8Pointer2
..更改一个影响另一个..
现在,您决定执行以下操作:
let uint8Pointer1 = UnsafeMutablePointer<UnsafeMutablePointer<Float>?>!.init(&uint8Pointer)
uint8Pointer1?.initialize(from: &uint8Pointer, count: 8)
在这里,您创建了一个指针( uint8Pointer1
)到uint8Pointer
和你说uint8Pointer1
初始化uint8Pointer
..但是你初始化的指针本身和8计数指针..
首先,不要打扰在指向具有自身值的指针的指针上调用initialize。它已经指向了正确的值。
很好的是:
uint8Pointer1?.initialize(from: &uint8Pointer, count: 1)
//Same as: memcpy(uint8Pointer1, &uint8Pointer, sizeof(uint8Pointer)`
//However, they both point to the same memory address..
将崩溃,但是:
uint8Pointer1?.initialize(from: &uint8Pointer)
//Same as: `uint8Pointer1 = uint8Pointer`.. Note: Just a re-assignment.
不会..因为它不会对后者memcpy
,而前者却不会。
希望我能正确解释。
PS正确命名您的变量!
C ++人士的翻译:
//Initial pointer to array..
float bytes2[] = {39, 77, 111, 111, 102, 33, 39, 0};
float* uint8Pointer2 = &bytes[2];
memcpy(uint8Pointer2, &bytes2[0], bytes2.size() * sizeof(float));
//Shallow/Shadowing Pointer...
float* uint8Pointer = uint8Pointer2;
float bytes[] = {391, 771, 1111, 1111, 1012, 331, 319, 10};
memcpy(uint8Pointer, &bytes[0], bytes.size() * sizeof(float));
//Pointer to pointer..
float** uint8Pointer1 = &uint8Pointer;
//Bad.. uint8Pointer1 and &uint8Pointer is the same damn thing (same memory address)..
//See the line above (float** uint8Pointer1 = &uint8Pointer)..
memcpy(uint8Pointer1, &uint8Pointer, 8 * sizeof(uint8Pointer));
//The memcpy is unnecessary because it already pointers to the same location.. plus it's also wrong lol.
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