STL algorithm replace, replace_if and replace_copy, replace_copy_if (49)

Replace prototype:

STD: replace

template <class ForwardIterator, class T>  void replace (ForwardIterator first, ForwardIterator last,                const T& old_value, const T& new_value);

Replace a value in the specified range with a new value.

The behavior is similar:

template <class ForwardIterator, class T>  void replace (ForwardIterator first, ForwardIterator last,                const T& old_value, const T& new_value){  while (first!=last) {    if (*first == old_value) *first=new_value;    ++first;  }}

Replace_if prototype:

STD: replace_if

template <class ForwardIterator, class UnaryPredicate, class T>  void replace_if (ForwardIterator first, ForwardIterator last,                   UnaryPredicate pred, const T& new_value );

Replace the value of the element whose Pred return value is true with new_value.

The behavior is similar:

template < class ForwardIterator, class UnaryPredicate, class T >  void replace_if (ForwardIterator first, ForwardIterator last,                   UnaryPredicate pred, const T& new_value){  while (first!=last) {    if (pred(*first)) *first=new_value;    ++first;  }}

A simple example of combining the two is as follows:

#include <iostream>#include <algorithm>#include <vector>using namespace std;void replaceif(){    vector<int> vi{1,2,3,4,4,6};    vector<int> v2{1,2,3,4,5,6};    cout<<"vi=";    for(int i:vi)        cout<<i<<" ";    cout<<endl;    cout<<"v2=";    for(int i:v2)        cout<<i<<" ";    cout<<endl;    cout<<"vi.size()="<<vi.size()<<endl;    cout<<"v2.size()="<<v2.size()<<endl;    replace(vi.begin(),vi.end(),4,888);    cout<<"after     replace(vi.begin(),vi.end(),4,888);"<<endl;    cout<<"vi=";    for(int i:vi)        cout<<i<<" ";    cout<<endl;    replace_if(v2.begin(),v2.end(),[](int n){return n%2==0;},999);    cout<<"after replace_if(v2.begin(),v2.end(),[](int n){return n%2==0;},999);"<<endl;    cout<<"v2=";    for(int i:v2)        cout<<i<<" ";    cout<<endl;    cout<<"vi.size()="<<vi.size()<<endl;    cout<<"v2.size()="<<v2.size()<<endl;}

Run:

Replace_copy prototype:

STD: replace_copy

template <class InputIterator, class OutputIterator, class T>  OutputIterator replace_copy (InputIterator first, InputIterator last,                               OutputIterator result,                               const T& old_value, const T& new_value);

Copy the elements in the range [first, last) to the start position of result one by one. If the element value is old_valus, replace the value with new_value.

The returned value is the iterator at the next position of the last element to be overwritten.

The behavior is similar:

template <class InputIterator, class OutputIterator, class T>  OutputIterator replace_copy (InputIterator first, InputIterator last,                               OutputIterator result, const T& old_value, const T& new_value){  while (first!=last) {    *result = (*first==old_value)? new_value: *first;    ++first; ++result;  }  return result;}

Replace_copy_if prototype:

STD: replace_copy_if

template <class InputIterator, class OutputIterator, class UnaryPredicate, class T>  OutputIterator replace_copy_if (InputIterator first, InputIterator last,                                  OutputIterator result, UnaryPredicate pred,                                  const T& new_value);

Copy the elements in the range [first, last) to the start position of result one by one. If the PRED returned value of an element is true, replace the value with new_value.

The returned value is the iterator at the next position of the last element to be overwritten.

The behavior is similar:

template <class InputIterator, class OutputIterator, class UnaryPredicate, class T>  OutputIterator replace_copy_if (InputIterator first, InputIterator last,                                  OutputIterator result, UnaryPredicate pred,                                  const T& new_value){  while (first!=last) {    *result = (pred(*first))? new_value: *first;    ++first; ++result;  }  return result;}

A simple example of combining the two is as follows:

#include <iostream>#include <algorithm>#include <vector>using namespace std;void replacecopyif(){    vector<int> vi{1,2,3,4,4,6};    vector<int> vresult1(6);    vector<int> vresult2(6);    cout<<"vi=";    for(int i:vi)        cout<<i<<" ";    cout<<endl;    cout<<"vreult1=";    for(int i:vresult1)        cout<<i<<" ";    cout<<endl;    cout<<"vreult2=";    for(int i:vresult2)        cout<<i<<" ";    cout<<endl;    replace_copy(vi.begin(),vi.end(),vresult1.begin(),4,888);    cout<<"after     replace(vi.begin(),vi.end(),vresult1.begin(),4,888);"<<endl;    cout<<"vresult1=";    for(int i:vresult1)        cout<<i<<" ";    cout<<endl;    replace_copy_if(vi.begin(),vi.end(),vresult2.begin(),[](int n){return n%2==0;},999);    cout<<"after replace_if(v2.begin(),v2.end(),vresult2.begin(),[](int n){return n%2==0;},999);"<<endl;    cout<<"vresult2=";    for(int i:vresult2)        cout<<i<<" ";    cout<<endl;}

Run:

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STL algorithm replace, replace_if and replace_copy, replace_copy_if (49)