Managed C++ allows you to declare and use Managed .NET arrays which means you
don't have to do memory allocation of your own and garbage collection will take
care of memory de-allocation. Managed .NET arrays are basically objects of the
System::Array class and thus you have the additional benefit that you can call
methods of the System::Array class on your Managed .NET arrays. Both single and
multi-dimensional arrays are supported though the syntax is slightly different
from that used with old-style unmanaged arrays.
String* StrArray[] = new String* [5];
for(int i=0;i<5;i++)
StrArray[i] = i.ToString();
for(int i=0;i<5;i++)
Console::Write("{0} ",StrArray[i]);
Here the syntax is not much too different from that in unmanaged code, except that the array we create will be managed and thus garbage collected. Just as in unmanaged arrays, the array index is zero based.
int NumArray __gc[] = new int __gc[5];
for(int i=0;i<5;i++)
NumArray[i]=i;
for(int i=0;i<5;i++)
Console::Write("{0} ",__box(NumArray[i]));
For value types you have to explicitly use the __gc keyword when declaring
arrays. If we do not use the __gc keyword the new
operator will create an unmanaged array. But of course, the array members are
still native value types and thus we need to box them into managed types using
the __box keyword when passing them to Console::Write.
String* MultiString[,] = new String*[2,3];
for(int i=0;i<2;i++)
for(int j=0;j<3;j++)
MultiString[i,j] = String::Format("{0} * {1} = {2};",
__box(i),__box(j),__box(i*j));
for(int i=0;i<2;i++)
{
for(int j=0;j<3;j++)
Console::Write("{0} ",MultiString[i,j]);
Console::WriteLine();
}
Whoa! What's that, eh? Looks really weird, huh? I thought so too when I first came across the Managed C++ style of declaring Managed .NET arrays. You now have just one pair of brackets and each of the dimensional indexes are separated by commas. Unlike in unmanaged arrays, a 2-dimensional array is NOT an array of arrays. It is simply a 2-dimensional array.
Jagged arrays are multi-dimensional arrays that are non-rectangular. For example, you can have a 2-dimensional array where each of the single dimensional sub-arrays are of a different dimension. Unfortunately you cannot have jagged arrays in Managed C++ because there is currently no support for jagged arrays. What might piss you off even more is the fact that C# supports jagged arrays. But then you can always simulate jagged arrays which is what I did. It's not the same thing really, and I do hope they add jagged array support in the next release of VC++ .NET.
Array* Multi[] = new Array*[2];
Multi[0] = new String*[4];
Multi[1] = new String*[2];
for(int i=0;i<2;i++)
for(int j=0; j<Multi[i]->Length;j++)
Multi[i]->SetValue(String::Format("{0} * {1} = {2};",
__box(i),__box(j),__box(i*j)),j);
for(int i=0;i<2;i++)
{
for(int j=0; j<Multi[i]->Length;j++)
Console::Write("{0} ",Multi[i]->GetValue(j));
Console::WriteLine();
}
What I did was to create an array of System::Array objects and
then I initialized each of those System::Array objects to an array
of String objects. And we access an object as Multi[i]->GetValue(j)
where i and j are the dimensional indexes. I know that
some of you are groaning right now, but I couldn't find any alternative
solution. I have posted this in the VC++ .NET newsgroups too but haven't got any
responses.
static void MakeArrayUpper(String* TwoDArray[,])
{
for(int i=0;i <= TwoDArray->GetUpperBound(0); i++)
for(int j=0;j <= TwoDArray->GetUpperBound(1); j++)
TwoDArray[i,j]=TwoDArray[i,j]->ToUpper();
}
Well that was rather straightforward, wasn't it? I have used
GetUpperBound which is a member method of the System::Array
class on our array. As mentioned earlier and as I will explain later down below,
we can use any System::Array method on our arrays.
static void DoubleIntArray(int int_array __gc[])
{
for(int i=0; i< int_array->Length; i++)
int_array[i] *= 2;
}
Well this is just about similar to the previous version except that we have
used the __gc keyword here. One very interesting issue here is
that arrays of value types are passed by reference. This might seem odd at
first glance, but remember that the array itself is a System::Array
object and is thus a managed type which means it's always passed by reference.
static String* CreatePopulateDummyArray() [,]
{
String* Small[,] = new String* [2,2];
Small[0,0] = "Colin Davies";
Small[0,1] = "James T Johnson";
Small[1,0] = "Kannan Kalyanaraman";
Small[1,1] = "Roger Wright";
return Small;
}
LOL. I can imagine the incredulous look on some of your faces. For whatever reasons they might have had, Microsoft have decided to make it this way and so be it. After all this is C++ and it's not ever expected to make things easier for anyone. Well, so whenever we want to return a managed array, we suffix our function name with our array's dimensional order. Well, when you consider that in unmanaged C++ there was no way to actually return an array except by returning a pointer to it's first element, I must say that this is a great improvement. Now you can actually do something like this.
String* Small[,] = Test::CreatePopulateDummyArray();
Array::Sort(nArray);
for(int i=0;i<3;i++)
Console::Write("{0} ",__box(nArray[i]));
Console::WriteLine();
Array::Reverse(nArray);
for(int i=0;i<3;i++)
Console::Write("{0} ",__box(nArray[i]));
Console::WriteLine();
I have used Array::Sort and Array::Reverse on my arrays. Now isn't that
handy?
#include "stdafx.h"
#using <mscorlib.dll>
#include <tchar.h>
using namespace System;
__gc class Test
{
public:
static void MakeArrayUpper(String* TwoDArray[,])
{
for(int i=0;i <= TwoDArray->GetUpperBound(0); i++)
for(int j=0;j <= TwoDArray->GetUpperBound(1); j++)
TwoDArray[i,j]=TwoDArray[i,j]->ToUpper();
}
static String* CreatePopulateDummyArray() [,]
{
String* Small[,] = new String* [2,2];
Small[0,0] = "Colin Davies";
Small[0,1] = "James T Johnson";
Small[1,0] = "Kannan Kalyanaraman";
Small[1,1] = "Roger Wright";
return Small;
}
static void DoubleIntArray(int int_array __gc[])
{
for(int i=0; i< int_array->Length; i++)
int_array[i] *= 2;
}
};
int _tmain(void)
{
//Single dimensional arrays - reference types
String* StrArray[] = new String* [5];
for(int i=0;i<5;i++)
StrArray[i] = i.ToString();
for(int i=0;i<5;i++)
Console::Write("{0} ",StrArray[i]);
Console::WriteLine();
//Single dimensional arrays - value types
int NumArray __gc[] = new int __gc[5];
for(int i=0;i<5;i++)
NumArray[i]=i;
for(int i=0;i<5;i++)
Console::Write("{0} ",__box(NumArray[i]));
Console::WriteLine();
//Multi dimensional arrays
String* MultiString[,] = new String*[2,3];
for(int i=0;i<2;i++)
for(int j=0;j<3;j++)
MultiString[i,j] = String::Format("{0} * {1} = {2};",
__box(i),__box(j),__box(i*j));
for(int i=0;i<2;i++)
{
for(int j=0;j<3;j++)
Console::Write("{0} ",MultiString[i,j]);
Console::WriteLine();
}
//Simulating jagged arrays
Array* Multi[] = new Array*[2];
Multi[0] = new String*[4];
Multi[1] = new String*[2];
for(int i=0;i<2;i++)
for(int j=0; j<Multi[i]->Length;j++)
Multi[i]->SetValue(String::Format("{0} * {1} = {2};",
__box(i),__box(j),__box(i*j)),j);
for(int i=0;i<2;i++)
{
for(int j=0; j<Multi[i]->Length;j++)
Console::Write("{0} ",Multi[i]->GetValue(j));
Console::WriteLine();
}
//Passing arrays as arguments to functions and
//returning arrays back from the function
String* Small[,] = Test::CreatePopulateDummyArray();
for(int i=0;i<2;i++)
for(int j=0;j<2;j++)
Console::Write("{0} ",Small[i,j]);
Console::WriteLine();
Test::MakeArrayUpper(Small);
for(int i=0;i<2;i++)
for(int j=0;j<2;j++)
Console::Write("{0} ",Small[i,j]);
Console::WriteLine();
//Passing an int array by reference
int nArray __gc[] = new int __gc[3];
nArray[0] = 5;
nArray[1] = 7;
nArray[2] = 2;
for(int i=0;i<3;i++)
Console::Write("{0} ",__box(nArray[i]));
Console::WriteLine();
Test::DoubleIntArray(nArray);
for(int i=0;i<3;i++)
Console::Write("{0} ",__box(nArray[i]));
Console::WriteLine();
//Calling Array member methods
Array::Sort(nArray);
for(int i=0;i<3;i++)
Console::Write("{0} ",__box(nArray[i]));
Console::WriteLine();
Array::Reverse(nArray);
for(int i=0;i<3;i++)
Console::Write("{0} ",__box(nArray[i]));
Console::WriteLine();
return 0;
}
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