C ++声明数组，其大小值来自const数组

Question

I'm trying to define a stack c-style array whose size is taken from const array and is known in compile-time.

const int size[2]={100, 100};
int ar[size[0]]; //error: expression must have a constant value

It fails. How it can be fixed?

Answer 1

"array whose size is taken from const array and is known in compile-time "

With C++11 you can have :

constexpr int size[2]={100, 100}; // size[0] is Compile-time constant

Use -std=c++11 or -std=c++0x to compile

Answer 2

Some options (with varying degrees of popularity):

1. Use constexpr (not supported in Visual Studio)
2. Use a Vector
3. Use dynamic allocation
4. Use a const int (C99 or newer or C++)
5. Use an enum
6. Use a MACRO to define the size (since it's known at compile time)

Answer 3

C++ array sizes must be constant expressions, not just constant data. Array data, even though const, is not a constant expression.

array size and const