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Table 5-1. Differences Between Native and Managed Arrays
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Difference
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Underlying representation What s in the type
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Native Array
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A native array is a pointer to a block of memory.
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Managed Array
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A managed array is an object with properties and methods. Rank, not size.
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Rank, and size of each dimension except the last.
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C HA PTER 5 FUNDA MENTAL TYPES : STRINGS , ARRA YS , AN D E NUMS
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Table 5-1. Differences Between Native and Managed Arrays
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Difference
Stack or heap Allowed element types
Native Array
Arrays are created on the stack. Native types.
Managed Array
Arrays are created on the managed heap. Managed types, primitive types, or native pointers.
Arrays As Parameters
Using arrays as parameters and return values requires special care in C++, because the type of the array includes the length of all dimensions except one, as you can see by considering that the code in Listing 5-28 is legal in C++. An array with a dimension unequal to that specified in the function signature is accepted by the function g, and in fact the size of the first dimension does not even need to be specified in the function signature, as in the signature for f. This is because a classic C++ array is actually a pointer. For a pointer to be useful for operations such as incrementing and decrementing, the compiler needs to know the size of the objects pointed to in order to move the correct number of bytes ahead when incrementing; however, the compiler does not need to know the number of objects in a sequence. Listing 5-28. Passing an Array of Inconsistent Size // array_dimension_type.cpp // f takes an unspecified number of arrays 2 x 3 in size void f(int a[][2][3]) { } // g takes an array of 5 arrays 2 x 3 in size void g(int a[5][2][3]) { } int main() { int native_3d_array[5][2][3]; int native_3d_array2[15][2][3]; f(native_3d_array); f(native_3d_array2); g(native_3d_array); g(native_3d_array2); } For managed arrays, the rank (number of dimensions) is part of the type, but not the length of any of the dimensions. Thus, functions taking managed arrays should be written to handle arrays of any dimensional length.
// No error, but may result in a buffer overrun
CHAPTER 5 FUNDAMEN TA L TYPES: STRING S, A RRAY S, A ND ENUM S
Arrays are passed by reference, not by value. Managed arrays are passed by reference, like any reference type, so this behavior is the same. Listing 5-29 shows how to use a managed array as a function parameter. Listing 5-29. Using an Array As a Parameter // arrays_parameter.cpp using namespace System; // using an array as an argument void set_to_one(int i, array<int>^ array_arg) { // Change the array inside this function. array_arg[i] = 1; } int main() { array<int>^ array1 = { 0, 1 }; set_to_one(0, array1); // The output here is " 1 1", indicating that the array // change is made to the same array. Console::WriteLine(" {0} {1}", array1[0], array1[1]); } Arrays may be used as return values just as any reference type.
Copying an Array
If you use the assignment operator with arrays, you ll create another reference to the same array. In other words, the assignment operator is a shallow copy, just as you saw with String. If you want a deep copy, you need to use the static Array::Copy method. Listing 5-30 shows how. Listing 5-30. Making Copies of an Array // arrays_copy.cpp using namespace System; int main() { array<int>^ array1 = { 0, 1, 2};
C HA PTER 5 FUNDA MENTAL TYPES : STRINGS , ARRA YS , AN D E NUMS
// Shallow copy creates another name for the array. array<int>^ array2 = array1; array2[0] = 100; // This prints "100" since array2 is a synonym of array1. Console::WriteLine( "{0}", array1[0] ); array<int>^ array3 = gcnew array<int>(3); Array::Copy(array1, array3, array1->Length); // Change a value in the new copy of the array. array3[0] = 200; // This prints "100 1 2" since the old array was not affected. Console::WriteLine( "{0} {1} {2}", array1[0], array1[1], array1[2]); } Here is the output of Listing 5-30: 100 100 1 2
Managed Array Class Members
A managed array is actually an instance of the class System::Array. System::Array inherits from System::Object and implements IList. All managed arrays have the members shown in Tables 5-2 and 5-3.
Table 5-2. Some Public System::Array Properties
Property
Length LongLength Rank SyncRoot
Description
Returns the number of elements in all the dimensions of the array Returns lengths greater than the maximum 32-bit integer, 231 1 Returns the number of dimensions in the array Returns an object that can be used for thread synchronization
CHAPTER 5 FUNDAMEN TA L TYPES: STRING S, A RRAY S, A ND ENUM S
Table 5-3. Some Public System::Array Methods
Name of Method
AsReadOnly BinarySearch (various overloads) Clear Clone ConstrainedCopy generic ConvertAll Copy CopyTo CreateInstance Equals
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