(C++) std::replace_if

 

std::replace_if is an STL algorithm to replace elements of a sequence (on a std::vector, for example) that satisfy a certain predicate. Use std::replace if no predicate is needed (that is: a certain value must always be replaced).

 

Prefer algorithms over hand-written loops [1-3]. Exercise #9: No for-loops shows how to remove hand-written loops.

 

 

 

 

 

Example

 

The code below shows how to replace all values that are negative to zero:

 

---

#include <algorithm> #include <numeric> #include <vector> //From http://www.richelbilderbeek.nl/CppReplaceNegativeByZero.htm void ReplaceNegativeByZero(std::vector<int>& v) {   std::replace_if(v.begin(),v.end(),     std::bind2nd(std::less<int>(),0),0); }

 

 

 

 

 

replace_if function definition

 

Simplified and modified from the STL that ships with C++ Builder 6.0:

 

---

template <   class ForwardIter,   class Predicate,   class Tp > void replace_if(   ForwardIter first,   const ForwardIter last,   const Predicate pred,   const Tp& newvalue) {   for ( ; first != last; ++first)   {     if (pred(*first))     {       *first = newvalue;     }   } }

 

 

 

 

 

External links

 

• Cplusplus.com page about std::replace_if

 

 

 

 

 

References

 

1. Bjarne Stroustrup. The C++ Programming Language (3rd edition). ISBN: 0-201-88954-4. Chapter 18.12.1 : 'Prefer algorithms over loops'
2. Herb Sutter and Andrei Alexandrescu. C++ coding standards: 101 rules, guidelines, and best practices. ISBN: 0-32-111358-6. Chapter 84: 'Prefer algorithm calls to handwritten loops.'
3. Herb Sutter and Andrei Alexandrescu. C++ coding standards: 101 rules, guidelines, and best practices. ISBN: 0-32-111358-6. Chapter 88: 'Prefer function objects over functions as algorithm and comparer arguments.'