void replace( ForwardIt first, ForwardIt last,
<ForwardIt>::value_type >
constexpr void replace( ForwardIt first, ForwardIt last,
void replace( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last,
class T = typename std::iterator_traits
<ForwardIt>::value_type >
void replace( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last,
void replace_if( ForwardIt first, ForwardIt last,
class T = typename std::iterator_traits
<ForwardIt>::value_type> >
constexpr void replace_if( ForwardIt first, ForwardIt last,
class ForwardIt, class UnaryPred, class T >
void replace_if( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last,
class ForwardIt, class UnaryPred,
class T = typename std::iterator_traits
<ForwardIt>::value_type> >
void replace_if( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last,
Replaces all elements in the range [
first,
last)
with new_value if they satisfy specific criteria.
1) Replaces all elements that are equal to old_value (using operator==).
3) Replaces all elements for which predicate p returns true.
2,4) Same as (1,3), but executed according to policy.
These overloads participate in overload resolution only if all following conditions are satisfied:
If *first = new_value is invalid(until C++20)new_value is not writable to first(since C++20), the program is ill-formed.
[edit] Parameters first, last - the pair of iterators defining the range of elements to process old_value - the value of elements to replace policy - the execution policy to use p - unary predicate which returns âtrue if the element value should be replaced.The expression p(v) must be convertible to bool for every argument v
of type (possibly const) VT
, where VT
is the value type of ForwardIt
, regardless of value category, and must not modify v
. Thus, a parameter type of VT&is not allowed, nor is VT unless for VT
a move is equivalent to a copy(since C++11). â
ForwardIt
must meet the requirements of LegacyForwardIterator. -UnaryPred
must meet the requirements of Predicate. [edit] Complexity
Given \(\scriptsize N\)N as std::distance(first, last):
1,2) Exactly \(\scriptsize N\)N comparisons using operator==.
3,4) Exactly \(\scriptsize N\)N applications of the predicate p.
[edit] ExceptionsThe overloads with a template parameter named ExecutionPolicy
report errors as follows:
ExecutionPolicy
is one of the standard policies, std::terminate is called. For any other ExecutionPolicy
, the behavior is implementation-defined.Because the algorithm takes old_value and new_value by reference, it can have unexpected behavior if either is a reference to an element of the range [
first,
last)
.
template<class ForwardIt, class T = typename std::iterator_traits<ForwardIt>::value_type> 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; }replace_if (3)
template<class ForwardIt, class UnaryPred, class T = typename std::iterator_traits<ForwardIt>::value_type> void replace_if(ForwardIt first, ForwardIt last, UnaryPred p, const T& new_value) { for (; first != last; ++first) if (p(*first)) *first = new_value; }[edit] Example
#include <algorithm> #include <array> #include <complex> #include <functional> #include <iostream> void println(const auto& seq) { for (const auto& e : seq) std::cout << e << ' '; std::cout << '\n'; } int main() { std::array<int, 10> s{5, 7, 4, 2, 8, 6, 1, 9, 0, 3}; // Replace all occurrences of 8 with 88. std::replace(s.begin(), s.end(), 8, 88); println(s); // Replace all values less than 5 with 55. std::replace_if(s.begin(), s.end(), std::bind(std::less<int>(), std::placeholders::_1, 5), 55); println(s); std::array<std::complex<double>, 2> nums{{{1, 3}, {1, 3}}}; #ifdef __cpp_lib_algorithm_default_value_type std::replace(nums.begin(), nums.end(), {1, 3}, {4, 2}); #else std::replace(nums.begin(), nums.end(), std::complex<double>{1, 3}, std::complex<double>{4, 2}); #endif println(nums); }
Output:
5 7 4 2 88 6 1 9 0 3 5 7 55 55 88 6 55 9 55 55 (4,2), (4,2)[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior LWG 283 C++98T
was required to be CopyAssignable (and EqualityComparable
replace
), but the value type of ForwardIt
is not
T
and T
is not always writable to ForwardIt
required *first = new_value
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