# Man Page replace_if.3

```
Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.

```

## NAME

```     replace_if

- Substitutes elements in a collection with new values.

```

## 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  parame-
ters,  then you always need to supply the Allocator template
argument. For instance, you need to write:

vector<int, allocator<int> >

vector<int>

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

```

```     replace, replace_copy, replace_copy_if

```