Please, help me to create a nested struct with an array. How do I fix this code?
class CMain
{
public:
CMain();
~CMain();
private:
struct
{
CCheckSum() : BufferSize(500) {memset(Buffer, 0, BufferSize);}
const int BufferSize;
char Buffer[BufferSize];
}SmallBuffer;
}
Thanks.
Even though you declared BufferSize as const, at class scope this does not declare a compile-time constant, which is needed for declaring array sizes in C++, but a constant data member, which, once set in the constructor, cannot be changed anymore for the lifetime of the instance (but can still be different for each instance).
Two solutions: Make
BufferSize static const at class scope, orconst at namespace scope (including global scope).
Static arrays need to know their length at compile time, or you need to dynamically allocate memory:
struct CCheckSum
{
CCheckSum()
: BufferSize(500),
Buffer(new char[BufferSize])
{
memset(Buffer, 0, BufferSize);
}
~CCheckSum() { delete[] Buffer; } // Note the use of delete[]!
const int BufferSize;
char* Buffer;
}SmallBuffer;
You're probably better off using std::vector though:
struct CCheckSum
{
CCheckSum() : Buffer(500, 0) {}
std::vector<char> Buffer; // A std::vector keeps
// track of its size enternally
}SmallBuffer;
std::(tr1::)array, not std::vector is the correct thing to use here, since the size is (supposed to be) a compile-time constant.
There is no problem related to the nesting.
Arrays have constant size. Either make BufferSize constant or use a std::vector instead of a char[].
Array size cannot be changed at run time. It should be known at compile time itself. You can use std::vector for this use case. Also, the struct name should be given before writing the constructor with the name CCheckSum.
struct CCheckSum
{
CCheckSum() : ....
