简而言之:它是迄今为止最节省内存的。

A std::string comes with a pointer, a length, and a "short-string-optimization" buffer. But my situation is I need to store a string that is almost always empty, in a structure that I have hundreds of thousands of. In C, I would just use char *, and it would be null most of the time. Which works for C++, too, except that a char * has no destructor, and doesn't know to delete itself. By contrast, a std::unique_ptr<char[]> will delete itself when it goes out of scope. An empty std::string takes up 32 bytes, but an empty std::unique_ptr<char[]> takes up 8 bytes, that is, exactly the size of its pointer.

最大的缺点是，每次我想知道字符串的长度，我必须调用strlen。

在一些Windows Win32 API调用中可以找到一个常见的模式，其中使用std::unique_ptr<T[]>可以派上用场，例如，当你调用一些Win32 API(将在该缓冲区中写入一些数据)时，不知道输出缓冲区应该有多大:

// Buffer dynamically allocated by the caller, and filled by some Win32 API function.
// (Allocation will be made inside the 'while' loop below.)
std::unique_ptr<BYTE[]> buffer;

// Buffer length, in bytes.
// Initialize with some initial length that you expect to succeed at the first API call.
UINT32 bufferLength = /* ... */;

LONG returnCode = ERROR_INSUFFICIENT_BUFFER;
while (returnCode == ERROR_INSUFFICIENT_BUFFER)
{
    // Allocate buffer of specified length
    buffer.reset( BYTE[bufferLength] );
    //        
    // Or, in C++14, could use make_unique() instead, e.g.
    //
    // buffer = std::make_unique<BYTE[]>(bufferLength);
    //

    //
    // Call some Win32 API.
    //
    // If the size of the buffer (stored in 'bufferLength') is not big enough,
    // the API will return ERROR_INSUFFICIENT_BUFFER, and the required size
    // in the [in, out] parameter 'bufferLength'.
    // In that case, there will be another try in the next loop iteration
    // (with the allocation of a bigger buffer).
    //
    // Else, we'll exit the while loop body, and there will be either a failure
    // different from ERROR_INSUFFICIENT_BUFFER, or the call will be successful
    // and the required information will be available in the buffer.
    //
    returnCode = ::SomeApiCall(inParam1, inParam2, inParam3, 
                               &bufferLength, // size of output buffer
                               buffer.get(),  // output buffer pointer
                               &outParam1, &outParam2);
}

if (Failed(returnCode))
{
    // Handle failure, or throw exception, etc.
    ...
}

// All right!
// Do some processing with the returned information...
...

出于二进制兼容性的考虑，您需要结构只包含一个指针。 你需要使用一个API来返回用new[]分配的内存 例如，您的公司或项目有一个禁止使用std::vector的一般规则，以防止粗心的程序员不小心引入副本 您希望防止粗心的程序员在这种情况下意外地引入副本。

有一个普遍的规则，c++容器比使用指针滚动自己的容器更受欢迎。这是一个普遍规律;它有例外。有更多的;这些只是例子。

I have used unique_ptr<char[]> to implement a preallocated memory pools used in a game engine. The idea is to provide preallocated memory pools used instead of dynamic allocations for returning collision requests results and other stuff like particle physics without having to allocate / free memory at each frame. It's pretty convenient for this kind of scenarios where you need memory pools to allocate objects with limited life time (typically one, 2 or 3 frames) that do not require destruction logic (only memory deallocation).

简而言之:它是迄今为止最节省内存的。

A std::string comes with a pointer, a length, and a "short-string-optimization" buffer. But my situation is I need to store a string that is almost always empty, in a structure that I have hundreds of thousands of. In C, I would just use char *, and it would be null most of the time. Which works for C++, too, except that a char * has no destructor, and doesn't know to delete itself. By contrast, a std::unique_ptr<char[]> will delete itself when it goes out of scope. An empty std::string takes up 32 bytes, but an empty std::unique_ptr<char[]> takes up 8 bytes, that is, exactly the size of its pointer.

最大的缺点是，每次我想知道字符串的长度，我必须调用strlen。

我对公认答案的精神再怎么反对也不为过。“最后的手段”?远非如此!

在我看来，与C语言和其他类似语言相比，c++最强大的特性之一是能够表达约束，以便在编译时检查它们，并防止意外误用。因此，在设计结构时，要问问自己它应该允许哪些操作。应该禁止所有其他用途，最好能够静态地(在编译时)实现这些限制，以免误用导致编译失败。

因此，当需要一个数组时，以下问题的答案指定了它的行为: 1. 它的大小是a)在运行时动态的，还是b)静态的，但只在运行时知道，还是c)静态的，在编译时知道? 2. 数组是否可以分配到堆栈上?

根据这些答案，我认为这是这种数组的最佳数据结构:

       Dynamic     |   Runtime static   |         Static
Stack std::vector      unique_ptr<T[]>          std::array
Heap  std::vector      unique_ptr<T[]>     unique_ptr<std::array>

是的，我认为unique_ptr<std::array>也应该被考虑，这两个都不是最后的工具。想想什么最适合你的算法。

所有这些都通过指向数据数组的原始指针(vector.data() / array.data() / uniquePtr.get())与普通C api兼容。

P. S. Apart from the above considerations, there's also one of ownership: std::array and std::vector have value semantics (have native support for copying and passing by value), while unique_ptr<T[]> can only be moved (enforces single ownership). Either can be useful in different scenarios. On the contrary, plain static arrays (int[N]) and plain dynamic arrays (new int[10]) offer neither and thus should be avoided if possible - which should be possible in the vast majority of cases. If that wasn't enough, plain dynamic arrays also offer no way to query their size - extra opportunity for memory corruptions and security holes.