algorithm.h

FB_for_each(It beg, It end, Func fn) implements a for loop that applies a function to each element of a container, passing as arguments each element and its neighboring elements. The previous element for the beginning element is the last element, and the next element for the last element is the first element.

std::vector<Point> polygon;
/* contains some points defining a polygon that has more than three points, *
 * no collinear edges, and no crossing edges                                */
bool isConvex = true; /* innocent before proven guilty */
bool isCCW = crossProduct(polygon[1] - polygon[0], polygon[2] - polygon[0]) > 0;
FB_for_each(convexPolygonVertices.begin(), convexPolygonVertices.end(),
  [&isConvex, isCCW](Point const& current, Point const& next, Point const& prev) {
    if(isConvex) { /* only needs to be concave once */
      bool isStillCCW = crossProduct(next - current, prev - current) > 0;
      if(isStillCCW != isCCW)
        isConvex = false;
    }
  });
/* if isConvex is still true, polygon defines a convex polygon, otherwise it's concave */

memory.h

make_unique<T>(Args...) from http://herbsutter.com/gotw/\_102/, the unique_pointer analog to make_shared()

auto x = make_unique< std::vector<int> >( 0, 1, 1, 2, 3, 5, 8, 13 );
/* x has type unique_pointer< std::vector<int> > *
 * *x contains { 0, 1, 1, 2, 3, 5, 8, 13 }       */

numerical.h

clamp(T x, T min, T max) limits the value of x to at most max and at least min

float x = 2.0f;           /* x == 2.0f */
x = clamp(x, 0.0f, 1.0f); /* x == 1.0f */

range.h

make_range(std::pair<It, It>) from http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2995.pdf, allows equal_range to be used with range-based for loops

for( auto const& x : make_range( mymap.equal_range(key) ) );