replace_if

Algorithm

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• Data Type and Member Function Indexes
• Synopsis
• Description
• Complexity
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Substitutes elements stored in a collection with new values.

None

#include <algorithm>

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

The replace_if algorithm replaces element referred to by iterator i in the range [first, last) with new_value when the following condition holds: pred(*i) == true.

Exactly last - first applications of the predicate are done.

//
// replace.cpp
//
 #include <algorithm>
 #include <vector>
 #include <iterator>
 #include <iostream.h>

 template<class Arg>
 struct all_true : public unary_function<Arg, bool>
 {
   bool operator()(const Arg&){ return 1; }
 };

 int main()
 {

   //Initialize a vector with an array of integers
   int arr[10] = {1,2,3,4,5,6,7,8,9,10};
   vector<int> v(arr, arr+10);

   //Print out original vector
   cout << "The original list: " << endl << "     ";
   copy(v.begin(),v.end(),ostream_iterator<int,char>(cout," "));
   cout << endl << endl;

   //Replace the number 7 with 11
   replace(v.begin(), v.end(), 7, 11);

   // Print out vector with 7 replaced, 
   // s.b. 1 2 3 4 5 6 11 8 9 10
   cout << "List after replace " << endl << "     ";
   copy(v.begin(),v.end(),ostream_iterator<int,char>(cout," "));
   cout << endl << endl;

   //Replace 1 2 3 with 13 13 13
   replace_if(v.begin(), v.begin()+3, all_true<int>(), 13);

   // Print out the remaining vector, 
   // s.b. 13 13 13 4 5 6 11 8 9 10
   cout << "List after replace_if " << endl << "     ";
   copy(v.begin(),v.end(),ostream_iterator<int,char>(cout," "));
   cout << endl << endl;

   return 0;
 }

Output :
The original list:
     1 2 3 4 5 6 7 8 9 10
List after replace:
     1 2 3 4 5 6 11 8 9 10
List after replace_if:
     13 13 13 4 5 6 11 8 9 10
List using replace_copy to cout:
     17 17 17 4 5 6 11 8 9 10
List with all elements output as 19s:
     19 19 19 19 19 19 19 19 19 19

If your compiler does not support default template parameters, then you need to always supply the Allocator template argument. For instance, you will need to write :

vector<int, allocator<int> >

instead of :

vector<int>

replace, replace_copy, replace_copy_if

©Copyright 1996, Rogue Wave Software, Inc.