(C++) Array

A way to store a a large number of values and access them by index. There are two kinds of arrays:

Static arrays (size known at compile-time)
Dynamically allocated arrays (size known at run-time)

Take care not to write beyond the bounds of an array [6].

Static arrays

//Create an array
int array[10];
//Initialize it with non-random values
for (int i=0; i!=10; ++i) array[i]=i;
//Square them
for (int i=0; i!=10; ++i) array[i]*=array[i];
//std::cout them
for (int i=0; i!=10; ++i) std::cout << array[i] << std::endl;

Prefer a std::vector over an array by default [1,2,3,5].

Static arrays cannot have a size of zero elements. This is used for compile-time assertions.

Tip

The Boost C++ Library supplies a class called boost::array, which might be chosen over a std::vector when there is no need of resizing at run-time.

How to determine a static array's size?

This can be done from the array's pointer and the size of the zero-th element:

include <iostream>

include <cassert>


int main()
{
  const int staticSize = 100;
  int myArray[staticSize];
  const int size = (sizeof(myArray)/sizeof(myArray[0]));
  std::cout << "staticSize: " << staticSize << std::endl;
  std::cout << "size: " << size << std::endl;
  assert(size==staticSize);
}

Dynamically allocated arrays

These array's sizes are unknown at compile-time and use new and delete[].

include <iostream>

include <cassert>


int main()
{
  const int randomSize = std::rand()%100;
  int * myArray = new int[randomSize];
  delete[] myArray;
}

Prefer a std::vector to dynamically allocated arrays [1,2,3,4,5].

How to determine a dynamically allocated array's size?

This can NOT[/red] be done from the array's pointer and the size of the zero-th element:

include <iostream>

include <cassert>


int main()
{
  const int randomSize = 2 + std::rand()%100; //Can never be 1
  int * myArray = new int[randomSize];
  const int size = (sizeof(myArray)/sizeof(myArray[0]));
  std::cout << "randomSize: " << randomSize << std::endl;
  std::cout << "size: " << size << std::endl;
  assert(size==1);
  assert(size!=randomSize);
  delete[] myArray;
}

'Array' links

C
C++ class (called boost::array)
C#
General
NQC

Code links

References

1) Bjarne Stroustrup. The C++ Programming Language (3rd edition).ISBN: 0-201-88954-4 Chapter 5.8.4 'Use vector and valarray rather than built-in (C-style) arrays'.
2) Herb Sutter and Andrei Alexandrescu. C++ coding standards: 101 rules, guidelines, and best practices. ISBN: 0-32-111358-6. Chapter 76: 'Use vector by default. Otherwise choose an appropriate container.'
3) Marshall Cline,Greg Lomow and Mike Girou. C++ FAQs. ISBN: 0-201-3098301, FAQ 28.02: 'Are arrays good or evil?' (Answer: 'Arrays are evil'
4) Scott Meyers. Effective STL. ISBN: 0-201-74962-9. Item 13: 'Prefer vector and string over dynamically allocated arrays'.
5) Bjarne Stroustrup. The C++ Programming Language (3rd edition).ISBN: 0-201-88954-4 Chapter C.14.11 'Prefer vector over array'.
6) Bjarne Stroustrup. The C++ Programming Language (3rd edition).ISBN: 0-201-88954-4 5.8.2: 'Take care not to write beyond the bounds of an array'.

last edited (November 7, 2007) by bilderbikkel, Number of views: 24654, Current Rev: 22 (Diff)

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