In C++ check if std::vector contains a certain value

Question

Is there any built in function which tells me that my vector contains a certain element or not e.g.

std::vector<string> v;
v.push_back("abc");
v.push_back("xyz");

if (v.contains("abc")) // I am looking for one such feature, is there any
                       // such function or i need to loop through whole vector?

http://stackoverflow.com/questions/507884/what-is-the-nicest-way-to-find-a-specific-string-in-vector — Ben, Nov 08 '12 at 02:28
As of C++11, this question is no longer a duplicate, as `std::any_of` now gives you a specific way to return true if a container CONTAINS a match, instead of using std::find to return a matching element. Thanks to @colddie for the original correct answer to this. — Nanki, Jun 15 '15 at 09:47

score 230 · Accepted Answer · edited Aug 28 '13 at 18:47

230

You can use std::find as follows:

if (std::find(v.begin(), v.end(), "abc") != v.end())
{
  // Element in vector.
}

To be able to use std::find: include <algorithm>.

edited Aug 28 '13 at 18:47

answered Jun 08 '11 at 10:59

AVH

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And what if the thing I'm trying to search is `argv`, which isn't a vector or an array (I'm trying to see if a certain command line argument option is present in the passed `argv`)? I created a vector containing all the "elements" of `argv` and applied your solution, though I'm not sure how clean that is. – pretzlstyle Nov 29 '17 at 22:45
1

@jphollowed `std::string const searchStr = "magic"; auto result = std::find_if(argv + 1, argv + argc, [&](char const * const arg) { return arg == searchStr; });` works. Not as clean and concise though. You'll need at least C++11 for that to compile. – AVH Nov 30 '17 at 07:56

score 43 · Answer 2 · edited Jul 06 '20 at 06:58

43

If your container only contains unique values, consider using std::set instead. It allows querying of set membership with logarithmic complexity.
```
 std::set<std::string> s;
 s.insert("abc");
 s.insert("xyz");
 if (s.find("abc") != s.end()) { ...
```
If your vector is kept sorted, use std::binary_search, it offers logarithmic complexity as well.
If all else fails, fall back to std::find, which is a simple linear search.

edited Jul 06 '20 at 06:58

William Miller

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answered Jun 08 '11 at 11:00

Alex B

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Even better, if you don't need an ordering on the strings, use a `std::tr1::unordered_set`, available from `` or ``, which has (almost) constant lookup and query time. With either set or unordered_set you can alternatively say `if (s.count("abc"))`. Don't forget to _accept_ one of the answers. – Kerrek SB Jun 08 '11 at 11:05
All three of these links seem to link to now-archived pages. – glhrmv Apr 09 '18 at 15:32

colddie · Answer 3 · 2018-12-30T00:18:21.680

24

In C++11, you can use std::any_of instead.

An example to find if there is any zero in the array:

std::array<int,3> foo = {0,1,-1};
if ( std::any_of(foo.begin(), foo.end(), [](int i){return i==0;}) )
std::cout << "zero found...";

edited Dec 30 '18 at 00:18

answered Feb 27 '13 at 03:34

colddie

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I find any_of much better than find, because find return an vector iterator to the element, and any_of return a boolean and much more suitable to if cases – TripleS Jan 11 '17 at 10:13
1

Can you add some more detail? An example of how to use and a link to the documentation. – j b Dec 05 '17 at 11:20
@JamieBullock have you seen this [answer](https://stackoverflow.com/a/31933118/8781554)? – Xam Mar 08 '18 at 00:44
3

@Xam Thanks. I know how to use `any_of`, I was encouraging colddie to improve the answer – j b Mar 08 '18 at 08:20

score 6 · Answer 4 · answered Jun 08 '11 at 10:58

6

it's in <algorithm> and called std::find.

answered Jun 08 '11 at 10:58

Nim

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score 3 · Answer 5 · answered Jun 08 '11 at 10:59

3

std::find().

answered Jun 08 '11 at 10:59

Oliver Charlesworth

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In C++ check if std::vector contains a certain value

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