## replace_if

    Algorithm

- Summary
- Data Type and Member Function Indexes
- Synopsis
- Description
- Complexity
- Example
- Warnings
- See Also

### Summary

Substitutes elements in a collection with new values.

### Data Type and Member Function Indexes
(exclusive of constructors and destructors)

None

### Synopsis

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

### Description

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`.

### Complexity

Exactly `last - first` applications of the predicate are done.

### Example

    //
    // replace.cpp
    //
     #include <algorithm>
     #include <vector>
     #include <iterator>
     #include <iostream>
     using namespace std;

     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;
     }

Program 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

### Warnings

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

`vector<int, allocator<int> >`

instead of:

`vector<int>`

If your compiler does not support namespaces, then you do not need the using declaration for `std`.

### See Also

replace, replace_copy, replace_copy_if

Copyright (c) 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.
OEM Release, June 1998