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(C++) std::vector

STL container for storing instances of any data type.

Example: create a std::vector

//Create an empty std::vector
std::vector<int> v;

//Create a std::vector with size 10, all elements zero
std::vector<int> v(10);

//Create a std::vector with size 10, all elements 42
std::vector<int> v(10, 42);

//Create a std::vector with one element: 10
std::vector<int> v{10};
std::vector<int> v = {10};

//Create a std::vector with two elements: 10 and 42
std::vector<int> v{10, 42};
std::vector<int> v = {10, 42};

Example: create a std::vector for another STL container

//Create a copy of a std::vector
std::vector<int> v(some_other_vector);
std::vector<int> v = some_other_vector; //Calls copy constructor, like above

//Create a std::vector with same elements as an STL container
std::vector<int> v(std::begin(some_container), std::end(some_container));

Example: convert argv to std::vector<std::string>

Because you can create a std::vector from two iterators, you can use argc and argv to get the command-line arguments in a std::vector<std::string>:

#include <cassert>
#include <string>
#include <vector>

int main(int argc, char* argv[])
{
  const std::vector<std::string> args(argv, argv + argc);
  assert(argc == static_cast<int>(args.size()));
  assert(argv[0] == args[0]);
}

Example: sorting a std::vector

#include <algorithm>
#include <cassert>
#include <vector>

int main()
{
  std::vector<int> v = {4, 2, 3, 1};
  std::sort(std::begin(v), std::end(v));
  const std::vector<int> expected = {1, 2, 3, 4};
  assert(v == expected);
}

std::vector versus plain array

Advantages of a std::vector over an array are:

  1. std::vector allocates memory from the free space when increasing in size
  2. std::vector is not a pointer in disguise [3]
  3. std::vector can increase/decrease in size run-time
  4. std::vector can do range checking (using at())

The erase-remove idiom

Calling std::remove to remove a certain value from a std::vector does not change a std::vector its size. std::remove does return an iterator to where the removed elements are put. This iterator can be used to call std::vector its 'erase' member function. These two operations are called the erase-remove idiom.

Use the erase-remove idiom the really remove a value from a std::vector.

std::vector code snippets

Note that among these are also more general container code snippets.

  1. AllAboutEqual, check if all doubles in a std::vector are about equal
  2. Append two std::vectors, Append
  3. Append, append two std::vectors
  4. Check if all doubles in a std::vector are about equal, AllAboutEqual
  5. CreateVector, create a std::vector from three values
  6. Convert Matrix<X> to Matrix<Y>, ConvertMatrix
  7. Convert std::vector<std::vector<X> > to std::vector<std::vector<Y> >, ConvertMatrix
  8. Convert two 2D std::vector<X> to 2D std::vector<Y>, ConvertMatrix
  9. ConvertMatrix, convert Matrix<X> to Matrix<Y>
  10. ConvertMatrix, convert std::vector<std::vector<X> > to std::vector<std::vector<Y> >
  11. ConvertMatrix, convert two 2D std::vector<X> to 2D std::vector<Y>
  12. CoutVector, std::cout on a std::vector
  13. GetIncVector, get a std::vector of incremented values (for example with values 0,1,2,3,etc)
  14. GetLongestString, find the length of the std::string with the most characters in a container
  15. GetShortestString, find the length of the std::string with the least characters in a container
  16. HugeVector, class that can contain more elements than std::vector
  17. LoopReader, reading a container looped
  18. RandomShuffle, shuffle a std::vector to a random order
  19. Read and write a std::vector from/to a std::stream
  20. Read and write two std::vectors from/to a std::stream
  21. Reading a container looped, LoopReader
  22. Save a container to file, SaveContainer
  23. SaveContainer, save a container to file
  24. SumStringLength, sum the lengths of std::strings irn a container
  25. Shuffle a std::vector to a random order, RandomShuffle
  26. Sort a std::vector, SortVector
  27. SortVector, sort a std::vector
  28. Write and read a std::vector to/from a std::stream
  29. Write and read two std::vectors to/from a std::stream
  30. std::cout on a std::vector, CoutVector

Advice

External links

References

  • [1] Herb Sutter, Andrei Alexandrescu. C++ coding standards: 101 rules, guidelines, and best practices. 2005. ISBN: 0-32-111358-6. Chapter 76: 'Use vector by default. Otherwise, choose an appropriate container'.
  • [2] Herb Sutter, Andrei Alexandrescu. C++ coding standards: 101 rules, guidelines, and best practices. 2005. ISBN: 0-32-111358-6. Chapter 77: 'Use vector and string instead of arrays'.
  • [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] Bjarne Stroustrup. The C++ Programming Language (3rd edition). 1997. ISBN: 0-201-88954-4. Chapter C.14.11 'Prefer vector over array'.
  • [5] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 31.6. Advice. page 924: '[2] Use vector as your default container'
  • [6] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 31.6. Advice. page 924: '[21] Don't use iterators into a resized vector or deque'
  • [7] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 31.6. Advice. page 924: '[19] Don't assume performance benefits from reserve() without measurements'
  • [8] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 31.6. Advice. page 924: '[22] When necessary, use reserve() to make performance predictable'
  • [9] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 31.6. Advice. page 924: '[23] Do not assume that [] range checks'
  • [10] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 31.6. Advice. page 924: '[24] Use at() when you need guaranteed range checks'
  • [11] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 31.6. Advice. page 924: '[25] Use emplace() for notational convenience'
  • [12] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 31.6. Advice. page 925: '[27] Use emplace() to avoid having to pre-initialize variables'
  • [13] Jason Turner. C++ Weekly - Ep 108 - Understanding emplace_back