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std::search

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< cpp‎ | algorithm
Revision as of 12:58, 15 January 2013 by Cubbi (Talk | contribs)

 
 
 

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Defined in header <algorithm>
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template< class ForwardIt1, class ForwardIt2 >

ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,

                   ForwardIt2 s_first, ForwardIt2 s_last );
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<td > (1) </td> <td class="t-dcl-nopad"> </td> </tr> <tr class="t-dcl ">

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template< class ForwardIt1, class ForwardIt2, class BinaryPredicate >

ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,

                   ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p );
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<td > (2) </td> <td class="t-dcl-nopad"> </td> </tr> Template:ddcl list end

Searches for the first subsequence of elements [s_first, s_last) in the range [first, last - (s_last - s_first)). The first version uses operator== to compare the elements, the second version uses the given binary predicate p.

Contents

Parameters

first, last - the range of elements to examine
s_first, s_last - the range of elements to search for
p - binary predicate which returns ​true if the elements should be treated as equal.

The signature of the predicate function should be equivalent to the following:

 bool pred(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function must not modify the objects passed to it.
The types Type1 and Type2 must be such that objects of types ForwardIt1 and ForwardIt2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively.

Type requirements
-
ForwardIt1, ForwardIt2 must meet the requirements of ForwardIterator.

Return value

Iterator to the beginning of first subsequence [s_first, s_last) in the range [first, last - (s_last - s_first)). If no such subsequence is found, last is returned.
If [s_first, s_last) is empty, first is returned. (since C++11)

Complexity

At most S*N comparisons where S = std::distance(s_first, s_last) and N = std::distance(first, last).

Possible implementation

First version
template<class ForwardIt1, class ForwardIt2>
ForwardIt1 search(ForwardIt1 first, ForwardIt1 last,
                        ForwardIt2 s_first, ForwardIt2 s_last)
{
    for (; ; ++first) {
        ForwardIt1 it = first;
        for (ForwardIt2 s_it = s_first; ; ++it, ++s_it) {
            if (s_it == s_last) {
                return first;
            }
            if (it == last) {
                return last;
            }
            if (!(*it == *s_it)) {
                break;
            }
        }
    }
}
Second version
template<class ForwardIt1, class ForwardIt2, class BinaryPredicate>
ForwardIt1 search(ForwardIt1 first, ForwardIt1 last,
                        ForwardIt2 s_first, ForwardIt2 s_last, 
                        BinaryPredicate p)
{
    for (; ; ++first) {
        ForwardIt1 it = first;
        for (ForwardIt2 s_it = s_first; ; ++it, ++s_it) {
            if (s_it == s_last) {
                return first;
            }
            if (it == last) {
                return last;
            }
            if (!p(*it, *s_it)) {
                break;
            }
        }
    }
}

Example

#include <string>
#include <algorithm>
#include <iostream>
 
template<typename Container>
bool in_quote(const Container& cont, const std::string& s)
{
    return std::search(cont.begin(), cont.end(), s.begin(), s.end()) != cont.end();
}
 
int main()
{
    std::string str = "why waste time learning, when ignorance is instantaneous?";
    // str.find() can be used as well
    std::cout << std::boolalpha << in_quote(str, "learning") << '\n'
                                << in_quote(str, "lemming")  << '\n';
 
    std::vector<char> vec(str.begin(), str.end());
    std::cout << std::boolalpha << in_quote(vec, "learning") << '\n'
                                << in_quote(vec, "lemming")  << '\n';
}

Output:

true
false
true
false

See also

Template:cpp/algorithm/dcl list find endTemplate:cpp/algorithm/dcl list equalTemplate:cpp/algorithm/dcl list findTemplate:cpp/algorithm/dcl list lexicographical compareTemplate:cpp/algorithm/dcl list mismatchTemplate:cpp/algorithm/dcl list search n