I would like to have an array which has a length that depends on the parameter of my template, but I keep getting the "expected constant expression" error.
enum MyEnum
{
FIRST,
OTHER
};
template<MyEnum e>
struct MyTemplate
{
static const int arrSize;
int myArr[arrSize]; // error C2057: expected constant expression
// int myArr[e == FIRST ? 4 : 10]; // works, but isn't very readable...
};
template<>
const int MyTemplate<FIRST>::arrSize = 4;
template<>
const int MyTemplate<OTHER>::arrSize = 10;
The compiler I must use does not support constexpr
, or any other C++ 11 features, and I also cannot pass the array size as a template parameter.
edit: I also must not use new
.
Thanks
In some cases like this, I'll add a function get_array_size<e>()
. Since you say you don't have constexpr, there's still decent possibilities:
//I call this a pseudo-template-function, but there's probably better names
template<MyEnum> struct GetArraySize; //compiler error for default
template<> struct GetArraySize<FIRST> {static const int value=4;};
template<> struct GetArraySize<OTHER> {static const int value=10;};
template<MyEnum e>
struct MyTemplate
{
static const int arrSize = GetArraySize<e>::value;
int myArr[arrSize];
};
Are we reinventing the wheel here ? Enums are compile time constants . Just do this :
enum MyEnum
{
FIRST = 4,
OTHER = 10
};
template<MyEnum e>
struct MyTemplate
{
int myArr[e];
};
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.