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Difference between revisions of "cpp/algorithm/search"

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< cpp‎ | algorithm
m (Text replace - "constexpr " to " ")
m (Text replace - "{{concept" to "{{named req")
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:@3@ Elements are compared using the given binary predicate {{tt|p}}.
 
:@3@ Elements are compared using the given binary predicate {{tt|p}}.
 
:@2,4@ Same as {{v|1,3}}, but executed according to {{tt|policy}}. These overloads do not participate in overload resolution unless {{c|std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>}} is true
 
:@2,4@ Same as {{v|1,3}}, but executed according to {{tt|policy}}. These overloads do not participate in overload resolution unless {{c|std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>}} is true
−
@5@ Searches the sequence {{math|[first, last)}} for the pattern specified in the constructor of {{tt|searcher}}. Effectively executes {{c|return searcher(first, last).first;}}.  {{concept|Searcher}} need not be {{concept|CopyConstructible}}.  
+
@5@ Searches the sequence {{math|[first, last)}} for the pattern specified in the constructor of {{tt|searcher}}. Effectively executes {{c|return searcher(first, last).first;}}.  {{named req|Searcher}} need not be {{named req|CopyConstructible}}.  
  
 
{{rev begin}}
 
{{rev begin}}

Revision as of 14:19, 15 June 2018

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Defined in header <algorithm>
(1)
template< class ForwardIt1, class ForwardIt2 >

ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,

                   ForwardIt2 s_first, ForwardIt2 s_last );
 (until C++20)
template< class ForwardIt1, class ForwardIt2 >

constexpr ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,

                             ForwardIt2 s_first, ForwardIt2 s_last );
 (since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 >

ForwardIt1 search( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last,

                   ForwardIt2 s_first, ForwardIt2 s_last );
 (2) (since C++17)
(3)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate >

ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,

                   ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p );
 (until C++20)
template< class ForwardIt1, class ForwardIt2, class BinaryPredicate >

constexpr ForwardIt1 search( ForwardIt1 first, ForwardIt1 last,

                             ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p );
 (since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class BinaryPredicate >

ForwardIt1 search( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last,

                   ForwardIt2 s_first, ForwardIt2 s_last, BinaryPredicate p );
 (4) (since C++17)
(5)
template<class ForwardIterator, class Searcher>

ForwardIterator search( ForwardIterator first, ForwardIterator last,

                        const Searcher& searcher );
 (since C++17)
(until C++20)
template<class ForwardIterator, class Searcher>

constexpr ForwardIterator search( ForwardIterator first, ForwardIterator last,

                                  const Searcher& searcher );
 (since C++20)
1-4) Searches for the first occurrence of the subsequence of elements [s_first, s_last) in the range [first, last - (s_last - s_first)).
1) Elements are compared using operator==.
3) Elements are compared using the given binary predicate p.
2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true
5) Searches the sequence [first, last) for the pattern specified in the constructor of searcher. Effectively executes return searcher(first, last).first;. Searcher need not be CopyConstructible.

The standard library provides the following searchers:

(C++17)
 standard C++ library search algorithm implementation
(class template) [edit]
(C++17)
 Boyer-Moore search algorithm implementation
(class template) [edit]
(C++17)
 Boyer-Moore-Horspool search algorithm implementation
(class template) [edit]
(since C++17)

Contents

Parameters

first, last - the range of elements to examine
s_first, s_last - the range of elements to search for
policy - the execution policy to use. See execution policy for details.
searcher - the searcher encapsulating the search algorithm and the pattern to look 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);

While the signature does not need to have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1 & is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy(since C++11)).
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

Template:par req concept Template:par req concept

Return value

1-4) 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)
5) Returns the result of searcher.operator(), that is, an iterator to the location at which the substring is found or a copy of last if it was not found.

Complexity

1-4) At most S*N comparisons where S = std::distance(s_first, s_last) and N = std::distance(first, last).
5) Depends on the searcher

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

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

Run this code
#include <string>
#include <algorithm>
#include <iostream>
#include <vector>
#include <functional>
 
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';
 
    // The C++17 overload demo:
    std::string in = "Lorem ipsum dolor sit amet, consectetur adipiscing elit,"
                     " sed do eiusmod tempor incididunt ut labore et dolore magna aliqua";
    std::string needle = "pisci";
    auto it = std::search(in.begin(), in.end(),
                   std::boyer_moore_searcher(
                      needle.begin(), needle.end()));
    if(it != in.end())
        std::cout << "The string " << needle << " found at offset "
                  << it - in.begin() << '\n';
    else
        std::cout << "The string " << needle << " not found\n";
}

Output: 

true
false
true
false
The string pisci found at offset 43

See also

 finds the last sequence of elements in a certain range
(function template) [edit]
returns true if one sequence is a subsequence of another
(function template) [edit]
determines if two sets of elements are the same
(function template) [edit]
(C++11)
 finds the first element satisfying specific criteria
(function template) [edit]
returns true if one range is lexicographically less than another
(function template) [edit]
finds the first position where two ranges differ
(function template) [edit]
searches for the first occurrence of a number consecutive copies of an element in a range
(function template) [edit]
(C++17)
 standard C++ library search algorithm implementation
(class template) [edit]
(C++17)
 Boyer-Moore search algorithm implementation
(class template) [edit]
(C++17)
 Boyer-Moore-Horspool search algorithm implementation
(class template) [edit]
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