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Algorithms (Modern C++)

For modern C++ programming, we recommend that you use the algorithms in the Standard Template Library (STL). Here are some important examples:

  • for_each , which is the default traversal algorithm. (Also transform for not-in-place semantics.)

  • find_if , which is the default search algorithm.

  • sort , lower_bound, and the other default sorting and searching algorithms.

To write a comparator, use strict < and use named lambdas when you can.

auto comp = []( const widget& w1, const widget& w2 )
      { return w1.weight() < w2.weight(); }

sort( v.begin(), v.end(), comp );

auto i = lower_bound( v.begin(), v.end(), comp );

When possible, use range-based for loops or algorithm calls, or both, instead of hand-written loops. copy, transform, count_if, remove_if, and others like them are much better than handwritten loops because their intent is obvious and they make it easier to write bug-free code. Also, many STL algorithms have implementation optimizations that make them more efficient.

Instead of old C++ like this:

for( auto i = strings.begin(); i != strings.end(); ++i ) {
  :::
  :::
}

auto i = v.begin();

for( ; i != v.end(); ++i ) {
  if (*i > x && *i < y) break;
}

Use modern C++ like this:

for_each( begin(strings), end(strings), []( string& s ) {
  :::
  :::
} );
auto i = find_if( begin(v), end(v),  [=](int i) { return i > x && i < y; }  );

The range-based for loop is a C++11 language feature, not an STL algorithm. But it deserves mention in this discussion about loops. Range-based for loops are an extension of the for keyword and provide a convenient and efficient way to write loops that iterate over a range of values. STL containers, strings, and arrays are ready-made for range-based for loops. To enable this new iteration syntax for your user-defined type, add the following support:

  • A begin method that returns an iterator to the beginning of the structure and an end method that returns an iterator to the end of the structure.

  • Support in the iterator for these methods: operator*, operator!=, and operator++ (prefix version).

These methods can be either members or stand-alone functions.

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