Thread: Enum as array

Originally Posted by antred

That's not my point. Let me show you what I was getting at.

I was apparently in the middle of my point when you stopped reading.

Code:

State* states = 0;
...
if ((states = new (std::nothrow) State[size]) != 0)
   ...

I don't really find fault with code like this, although, like I said, new generally throws when it fails so you might not want to do this anyway. There is no way you could dereference states and cause problems. It's an idiosyncrasy that is about as indefensible as others.

Originally Posted by Dontgiveup

Not sure that is a good idea. I think, and someone correct me if I am wrong, in C++, unless you assign values, everything remains undefined.

bool

int

float

double

Seems like all have been initialized by default.

Originally Posted by R41D3N

bool

int

float

double

Seems like all have been initialized by default.

I can do that too.
C++ code - 11 lines - codepad

Context matters. In this case the only reason that bool arrays may be initialized is because you wrote a new statement in the initializer list. Ordinarily, plain old data is not constructed at all, but the compiler can generate constructors for them, and they can be called.

I don't recommend calling new in the initializer list anyway. Because you have to handle the exception that might be thrown. And I seem to recall that code not working for microsoft compilers.

Originally Posted by whiteflags

I can do that too.
C++ code - 11 lines - codepad

That is actually initializing (afaik), the values are 0 within the error margins of double.

It's not. If it were initialized, it would say zero. It so happens that zero is also a common value in memory, so if you take a random selection of bytes and treat them as doubles, you will likely get (unnormalized) values close to zero.

I can do that too.

I can too! Mine is better!

Soma

Code:

#include <iostream>

using namespace std;

void T1()
{
    float a;
    cout << a << '\n';
}

void T2()
{
    float a(4.0f);
    cout << a << '\n';
}

void T3()
{
    float a;
    cout << a << '\n';
}

void T4()
{
    int a;
    cout << a << '\n';
}

void T5()
{
    int a(16);
    cout << a << '\n';
}

void T6()
{
    int a;
    cout << a << '\n';
}

void T7()
{
    int * a(new int[10]);
    for(unsigned int c(0); c < 10; ++c)
    {
        cout << a[c] << '\n';
    }
    delete[] a;
}

void T8()
{
    int * a(new int[10]);
    for(unsigned int c(0); c < 10; ++c)
    {
        a[c] = c;
        cout << a[c] << '\n';
    }
    delete[] a;
}

void T9()
{
    int * a(new int[10]);
    for(unsigned int c(0); c < 10; ++c)
    {
        cout << a[c] << '\n';
    }
    delete[] a;
}

int main()
{
    T1();
    T2();
    T3();
    T4();
    T5();
    T6();
    T7();
    T8();
    T9();
    return(0);
}

Code:

6.00414e-039
4
4
1082130432
16
16
4063968
4063968
0
0
0
0
0
0
0
0
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9

Sorry, turns out it was the compiler in that site. Tried the same code with MinGW and it returns garbage :P.

@Dontgiveup: Your best bet then is fill()

Originally Posted by whiteflags

I was apparently in the middle of my point when you stopped reading.

Yes, I may have misread your post. Sorry about that. But still, the example you gave doesn't preclude putting declaration and initialization in one statement:

Code:

if ( States* states = new (std::nothrow) State[size] )
{
	// ...
}

I didn't mean to preclude anything, but wouldn't that make the scope of states really weird, as in the if statement block?

Well yeah, it would only be accessible in the if and else blocks. If you need access beyond that scope then this method isn't applicable.

Originally Posted by Elysia

@OP:
You can assign enums to other variables because they are treated as ints due to their C heritage.
Yes, that means you can assigns Cars to Fruits (assuming enums here) too!
That said, this is all bad practise, so do not do it.
You may also want to read about strong enums and initializer lists (both C++11 features).

Thanks, so I guess the answer to my question is no. That it is not possible to initialise a dynamic array in an initialisation list. Instead of, as am doing now:

Code:

class Test {
bool * test;

public:
void init() {
test = new bool [10];
for(int i = 0; i < 10; ++i) test[i] = false;
Test () : test(0) {init();}
};

something like:

Code:

class Test {
bool * test;

public:
Test () : test(new bool [10]{false})//initalise it with default false values
};

Originally Posted by Elysia

It most definitely is possible. I haven't tried this myself, but something like this should work:

Code:

class Test
{
	std::vector<myenum> m_Vec;
	Test(): m_Vec({ e1, e2, e3, ... }) {}
};

Requires a modern compiler with C++11 initializer lists support.

Unfortunately, we can't use predefine data structure. This is part of a programming assignment where we are supposed to make our own hashtable (add remove, sorting etc.) using our own functions, STL data structures not permitted. I have done everything well and so far all is working well. I was just on the lookout for inefficiencies in my program, and what, where and how I maybe able to improve.