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我想制作一个程序，现在可以说表示一个矩阵，该矩阵将由一个向量表示，该向量中的每个对象都将表示一个单元格示例：vector now 当构造矩阵时，构造函数接收要插入的单元格列表矩阵。列表的大小在编译时是未知的

我有兴趣在不使用堆内存的情况下创建这个矩阵。换句话说，不使用“new”或“delete”这个词创建对象，如果我不知道有多少对象要插入向量中，有什么办法吗？

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有一种特殊的方法可以使用 new 在堆栈中分配内存，或者使用所谓的放置 new 运算符作为静态存储。使用这个版本的 new，你保留了一块内存，并且你明确地告诉 new 你想在哪里存储一个特定的变量。它将按如下方式工作：

   #include <new>
   int main()
   {
      char buffer[500];  // chunk of memory
      int p*;
      p = new (buffer) int[10];
   }

请注意，您需要包含新标头才能使用此特殊的新运算符。在这种情况下，当您使用自动存储时，内存将在离开声明它的块（主）时被释放。

参考资料：C++ Primer plus。第9章 第420页

于 2010-09-16T23:55:42.637 回答
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如果不使用汇编指令直接（因此依赖于平台）操作程序/函数的堆栈帧，就没有标准的方法可以做到这一点——我非常不鼓励这样做。是什么阻止您使用堆？

于 2010-09-16T23:21:24.637 回答
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用于alloca获取指针，然后使用就地new运算符：

void *p = alloca(sizeof(Class));
new (p) Whatever(arguments);

但是，请在使用前阅读alloca手册页！要非常小心。正如 Jim Brissom 所说，alloca不便携。

你不需要delete。函数返回时内存将被释放

于 2010-09-16T23:22:45.653 回答
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There is a way, it's very limiting and very unorthodox. You'll need to create a statically sized array of unsigned char which form a memory pool. There will be a limit to the size of the list of objects. You'll need to overload a new operator (and delete operator) for that class to specifically target such a memory pool.

That said, there's really no good reason to go this route.

于 2010-09-16T23:24:56.350 回答
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Well, if you don't want to use memory on the heap, where else do you want to get it from?

a) system dependant - you can ask the operating system to allocate some memory for you. But this is bad style (system dependant), and will use the same RAM... just in a different way allocated. For example, ::GlobalAlloc or ::LocalAlloc in Windows 32 will do such things if you are really interested in doing that.

b) memory mapped files - that might be interesting if you are asking because you think you'll have not enough RAM available and access time isn't an issue.

c) resort to C functions like malloc/free and cast the pointers... that is getting memory from the heap, just avoiding the "new" and "delete" keywords.

However, it is hard to tell what a "good" solution without information why you want to avoid new / delete. You have need for dynamic memory allocation, these two are the tools to do that.

Could you please explain/rephrase your question so you can get more precise answers?

于 2010-09-16T23:32:37.877 回答