std::replace

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.

#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

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)

Links:

http://en.cppreference.com/w/cpp/algorithm/replace

doc_CPP

2025-01-10 15:47:30

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