std::replace, std::replace_if

 

C++

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Technical Specifications

 

Algorithm library

Functions
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each countcount_if mismatch equal	findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n removeremove_if remove_copyremove_copy_if	replacereplace_if replace_copyreplace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) unique unique_copy
Partitioning operations
is_partitioned (C++11) partition partition_copy (C++11)	stable_partition partition_point (C++11)
Sorting operations (on sorted ranges)
is_sorted (C++11) is_sorted_until (C++11) sort	partial_sort partial_sort_copy stable_sort nth_element
Binary search operations (on sorted ranges)
lower_bound upper_bound	binary_search equal_range
Set operations (on sorted ranges)
merge inplace_merge includes	set_difference set_intersection set_symmetric_difference set_union
Heap operations
is_heap (C++11) is_heap_until (C++11) make_heap	push_heap pop_heap sort_heap
Minimum/maximum operations
max max_element min min_element minmax (C++11) minmax_element (C++11)	lexicographical_compare is_permutation (C++11) next_permutation prev_permutation
Numeric operations
iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <algorithm>
template< class ForwardIt, class T > void replace( ForwardIt first, ForwardIt last,               const T& old_value, const T& new_value );	(1)
template< class ForwardIt, class UnaryPredicate, class T > void replace_if( ForwardIt first, ForwardIt last,                  UnaryPredicate p, const T& new_value );	(2)

Replaces all elements satisfying specific criteria with new_value in the range [first, last). The first version replaces the elements that are equal to old_value, the second version replaces elements for which predicate p returns true.

Parameters

first, last	-	the range of elements to process
old_value	-	the value of elements to replace
p	-	unary predicate which returns ​true if the element value should be replaced. The signature of the predicate function should be equivalent to the following:  bool pred(const Type &a); The signature does not need to have const &, but the function must not modify the objects passed to it. The type Type must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to Type. ​
new_value	-	the value to use as replacement
Type requirements
- ForwardIt must meet the requirements of ForwardIterator.
- UnaryPredicate must meet the requirements of Predicate.

Return value

(none)

Complexity

Exactly last - first applications of the predicate.

Possible implementation

First version
template<class ForwardIt, class T> void replace(ForwardIt first, ForwardIt last, const T& old_value, const T& new_value) { for (; first != last; ++first) { if (*first == old_value) { *first = new_value; } } }
Second version
template<class ForwardIt, class UnaryPredicate, class T> void replace_if(ForwardIt first, ForwardIt last, UnaryPredicate p, const T& new_value) { for (; first != last; ++first) { if(p(*first)) { *first = new_value; } } }

Example

The following code at first replaces all occurrences of 8 with 88 in a vector of integers. Then it replaces all values less than 5 with 55.

Run this code

#include <algorithm>
#include <array>
#include <iostream>
#include <functional>
 
int main()
{
    std::array<int, 10> s{5, 7, 4, 2, 8, 6, 1, 9, 0, 3};
 
    std::replace(s.begin(), s.end(), 8, 88);
 
    for (int a : s) {
        std::cout << a << " ";
    }
    std::cout << '\n';
 
    std::replace_if(s.begin(), s.end(), 
                    std::bind(std::less<int>(), std::placeholders::_1, 5), 55);
    for (int a : s) {
        std::cout << a << " ";
    }
    std::cout << '\n';
}

Output:

5 7 4 2 88 6 1 9 0 3
5 7 55 55 88 6 55 9 55 55

See also

replace_copyreplace_copy_if	copies a range, replacing elements satisfying specific criteria with another value (function template)
std::experimental::parallel::replace (parallelism TS)	parallelized version of std::replace (function template)
std::experimental::parallel::replace_if (parallelism TS)	parallelized version of std::replace_if (function template)