C ++和Swift彼此不喜欢

I am trying to use a C++ library named MP4v2 in Swift. It is mostly working in that I can can call some functions, use some classes, etc.

我试图在Swift中使用名为MP4v2的C ++库。它主要是工作,我可以调用一些函数,使用一些类,等等。

I am having trouble with a particular function that returns a void pointer. It is NULL on failure, or some other value on success. There is a constant defined to check with, but neither that nor checking for nil works.

我遇到一个返回void指针的特定函数的问题。失败时为NULL,或成功时为其他值。有一个常量定义来检查,但既不检查也不检查nil是否有效。

if file != MP4_INVALID_FILE_HANDLE {

throws /<path_to_project>/main.swift:19:12: Use of unresolved identifier 'MP4_INVALID_FILE_HANDLE', but it is DOES exist (other constants work).

throws / /main.swift:19:12:使用未解析的标识符'MP4_INVALID_FILE_HANDLE',但它存在(其他常量有效)。

if file != NULL just causes the same problem, and if file != nil never is true, even if the function failed. What am I doing wrong?

if file!= NULL只会导致同样的问题,如果file!= nil永远不是真的,即使函数失败了。我究竟做错了什么?

1 个解决方案

#1

Looking at MP4v2 documentation, here is the definition of the macro to check for invalid handle:

查看MP4v2文档,这里是检查无效句柄的宏的定义:

 #define    MP4_INVALID_FILE_HANDLE   ((MP4FileHandle)NULL)

The reason it cannot be used in Swift is because it involves a NULL. In fact, if you define something like

它无法在Swift中使用的原因是因为它涉及NULL。事实上,如果你定义类似的东西

#define MY_NULL NULL

in your Objective-C(++) code and try to use it in Swift, Swift will suggest that you use nil instead.

在您的Objective-C(++)代码中尝试在Swift中使用它,Swift会建议您使用nil代替。

The handle type MP4FileHandle is

句柄类型MP4FileHandle是

typedef void *  MP4FileHandle

So, if you are calling a function like

所以,如果你正在调用类似的函数

MP4FileHandle aCPPFunction()

You should be able to check the return value as follows in Swift:

您应该能够在Swift中检查返回值,如下所示:

let h : MP4FileHandle = aCPPFunction()

if h != nil
{
   // The handle is valid and can be given as an argument to
   // other library functions.
}
else
{
   // The handle is NULL
}

I understand you tried this. It should work, please double-check. If for whatever strange reason this doesn't work for you, there are some other options:

我知道你试过这个。它应该工作,请仔细检查。如果由于任何奇怪的原因这对你不起作用,还有其他一些选择:

Write a simple helper function in C, C++, Objective-C or Objective-C++ to check if the handle is valid and return a integer flag, which should be easily understood by Swift.

用C,C ++,Objective-C或Objective-C ++编写一个简单的辅助函数来检查句柄是否有效并返回一个整数标志,Swift应该很容易理解。

Check h.hashValue. If it is 0, then the handle is invalid, otherwise it is valid. This is a bad undocumented hack, but it has worked for me. I would stay away from this one.

检查h.hashValue。如果为0,则句柄无效,否则有效。这是一个糟糕的无证件黑客,但它对我有用。我会远离这一个。

#1