英文:
Pass String to a method that accepts an UnsafeRawPointer parameter
问题
每次执行processUnsafeRawPointer(key)时，打印的结果为什么不同？
将String 直接传递给接受UnsafeRawPointer参数的方法时会发生什么？
var key = "Key"
func jump() {
print("\n测试UnsafeRawPointer")
processUnsafeRawPointer(key)
processUnsafeRawPointer(&key)
}
func processUnsafeRawPointer(_ key: UnsafeRawPointer) {
print(key)
}
public static func main() {
jump()
jump()
jump()
}
控制台输出：
测试UnsafeRawPointer
0x0000600000c104a0
0x000000010000d3c0
测试UnsafeRawPointer
0x0000600000c104a0
0x000000010000d3c0
测试UnsafeRawPointer
0x0000600000c18020
0x000000010000d3c0
英文:
Does anyone know why every time processUnsafeRawPointer(key) is executed, the printed result is different?
What happens when passing String directly to a method that accepts an UnsafeRawPointer parameter?
var key = "Key"
func jump() {
print("\ntest UnsafeRowPointer")
processUnsafeRawPointer(key)
processUnsafeRawPointer(&key)
}
func processUnsafeRawPointer(_ key: UnsafeRawPointer) {
print(key)
}
public static func main() {
jump()
jump()
jump()
}
Console:
test UnsafeRowPointer
0x0000600000c104a0
0x000000010000d3c0
test UnsafeRowPointer
0x0000600000c104a0
0x000000010000d3c0
test UnsafeRowPointer
0x0000600000c18020
0x000000010000d3c0
答案1
得分: 2
以下是翻译好的部分：
> 当您调用声明为接受UnsafePointer<Type>参数的函数时，可以传递以下任何一种：
- 如果Type是
Int8或UInt8，则可以传递String值。字符串将自动转换为以零结尾的UTF8缓冲区，并将该缓冲区的指针传递给函数。 - 包含可变变量、属性或下标引用的in-out表达式，其类型为
Type，将作为指向左侧标识符地址的指针传递。
当您调用接受UnsafeRawPointer参数的函数时，可以传递与UnsafePointer<Type>相同的操作数，但Type可以是任何类型。
processUnsafeRawPointer(key)是“String值”情况。将创建一个缓冲区。此缓冲区在内存中的某个位置分配，并且不必每次都在相同位置。
processUnsafeRawPointer(&key)是“in-out表达式”情况。由于key是一个var，这只会传递var的位置，而不会执行其他操作。
英文:
What actually happens is documented here:
> When you call a function that is declared as taking an
> UnsafePointer<Type> argument, you can pass any of the following:
>
> ...
>
> - A String value, if Type is Int8 or UInt8. The string is automatically converted to UTF8 in a zero-terminated buffer, and a
> pointer to that buffer is passed to the function.
> - An in-out expression that contains a mutable variable, property, or subscript reference of type Type, which is passed as a pointer to
> the address of the left-hand side identifier.
>
> ...
>
> When you call a function that takes an UnsafeRawPointer argument,
> you can pass the same operands as UnsafePointer<Type>, but with any
> type as Type.
processUnsafeRawPointer(key) is the "a String value" case. A buffer will be created. This buffer is allocated somewhere in memory, and doesn't have to be the same location every time.
processUnsafeRawPointer(&key) is the "an in-out expression" case. Since key is a var, this will just pass the location of the var, without doing anything else.
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