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(C++) std::vector

STL container for storing instances of any data type.

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.

Examples

• std::vector example 1: basics
• std::vector example 2: erase-remove idiom
• std::vector example 3: C++11 emplace member function
• std::vector example 4: remove an element with preserving the order
• std::vector example 5: returning a member std::vector that is not a copy

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

• Prefer using a std::vector over an array [1-4]
• Use std::vector as your default container [5]
• Don't use iterators into a resized std::vector or std::deque [6]
• Don't assume performance benefits from reserve() without measurements [7]
• When necessary, use reserve() to make performance predictable [8]
• Do not assume that operator[] range checks [9]
• Use the 'at' member function when you need guaranteed range checks [10]
• Use emplace() for notational convenience [11]
• Use emplace() to avoid having to pre-initialize variables [12]

External links

• CodePedia page about std::vector
• SGI page about std::vector
• Cplusplus.com page about std::vector

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'

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