C ++创建数组 [英] C++ creating arrays

问题描述

为什么我不能做这样的事情：

Why can't I do something like this:

int size = menu.size;
int list[size];

反正是有解决这个而不是使用矢量？ （阵列的速度更快，所以我想用数组）

Is there anyway around this instead of using a vector? (arrays are faster, so I wanted to use arrays)

感谢

推荐答案

的大小必须在编译时是已知的，因为编译器需要知道多少的堆栈空间将需要的分配足够内存吧。 （编辑：我站在纠正在C， 可以在栈上分配变长数组C ++不允许变长数组，但是。）

The size must be known at compile-time, since the compiler needs to know how much stack space will be needed to allocate enough memory for it. ( I stand corrected. In C, variable length arrays can be allocated on the stack. C++ does not allow variable length arrays, however.)

不过，您可以创建在的堆阵列的在运行时：

But, you can create arrays on the heap at run-time:

int* list = new int[size];

只要确保你释放内存，当你做，否则你会得到一个内存泄漏：

Just make sure you free the memory when you're done, or you'll get a memory leak:

delete [] list;

请注意，它很容易意外创建内存泄漏和矢量几乎肯定更容易使用和维护。载体的非常的快（特别是如果你储备（）他们到合适的规模第一），我强烈建议使用矢量代替人工记忆-management。

Note that it's very easy to accidentally create memory leaks, and a vector is almost for sure easier to use and maintain. Vectors are quite fast (especially if you reserve() them to the right size first), and I strongly recommend using a vector instead of manual memory-management.

在一般情况下，它是分析您的code，找出真正的瓶颈是不是一个好主意微优化前面（由于优化并不总是优化）。

In general, it's a good idea to profile your code to find out where the real bottlenecks are than to micro-optimize up front (because the optimizations are not always optimizations).

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