Algorithms are a fundamental part of the C++ Standard Library. Algorithms do not work with containers themselves but rather with iterators. Therefore, the same algorithm can be used by most if not all of the C++ Standard Library containers. This section discusses the conventions and terminology of the C++ Standard Library algorithms.
Remarks
The descriptions of the algorithm template functions employ several shorthand phrases:
The phrase "in the range [A, B)" means the sequence of zero or more discrete values beginning with A up to but not including B. A range is valid only if B is reachable from A; you can store A in an object N (N = A), increment the object zero or more times (++N), and have the object compare equal to B after a finite number of increments (N == B).
The phrase "each N in the range [A, B)" means that N begins with the value A and is incremented zero or more times until it equals the value B. The case N == B is not in the range.
The phrase "the lowest value of N in the range [A, B) such that X" means that the condition X is determined for each N in the range [A, B) until the condition X is met.
The phrase "the highest value of N in the range [A, B) such that X means that X is determined for each N in the range [A, B). The function stores in
Ka copy of N each time the condition X is met. If any such store occurs, the function replaces the final value of N, which equals B, with the value ofK. For a bidirectional or random-access iterator, however, it can also mean that N begins with the highest value in the range and is decremented over the range until the condition X is met.Expressions such as X - Y, where X and Y can be iterators other than random-access iterators, are intended in the mathematical sense. The function does not necessarily evaluate operator- if it must determine such a value. The same is also true for expressions such as X + N and X - N, where N is an integer type.
Several algorithms make use of a predicate that performs a pairwise comparison, such as with
operator==, to yield aboolresult. The predicate functionoperator==, or any replacement for it, must not alter either of its operands. It must yield the sameboolresult every time it is evaluated, and it must yield the same result if a copy of either operand is substituted for the operand.Several algorithms make use of a predicate that must impose a strict weak ordering on pairs of elements from a sequence. For the predicate
pr(X, Y):Strict means that
pr(X, X) is false.Weak means that X and Y have an equivalent ordering if !
pr(X, Y) && !pr(Y, X) (X == Y does not need to be defined).Ordering means that
pr(X, Y) &&pr(Y, Z) impliespr(X, Z).Some of these algorithms implicitly use the predicate X < Y. Other predicates that typically satisfy the strict weak ordering requirement are X > Y, less(X, Y), and
greater(X, Y). Note, however, that predicates such as X <= Y and X >= Y do not satisfy this requirement.A sequence of elements designated by iterators in the range [
First,Last) is a sequence ordered by operator< if, for each N in the range [0,Last-First) and for each M in the range (N,Last-First) the predicate !(*(First+ M) < *(First + N)) is true. (Note that the elements are sorted in ascending order.) The predicate function operator<, or any replacement for it, must not alter either of its operands. It must yield the sameboolresult every time it is evaluated, and it must yield the same result if a copy of either operand is substituted for the operand. Moreover, it must impose a strict weak ordering on the operands it compares.A sequence of elements designated by iterators in the range [
First,Last) is a heap ordered by operator< if, for each N in the range [1,Last-First) the predicate !(*First< *(First+ N)) is true. (The first element is the largest.) Its internal structure is otherwise known only to the template functions make_heap, [pop_heap]--brokenlink--(../Topic/not%20found:c10b0c65-410c-4c83-abf8-8b7f61bba8d0.md#pop_heap), and [push_heap]-brokenlink--(../Topic/not%20found:c10b0c65-410c-4c83-abf8-8b7f61bba8d0.md#push_heap). As with an ordered sequence, the predicate function operator<, or any replacement for it, must not alter either of its operands, and it must impose a strict weak ordering on the operands it compares. It must yield the sameboolresult every time it is evaluated, and it must yield the same result if a copy of either operand is substituted for the operand.The C++ Standard Library algorithms are located in the <algorithm> and <numeric> header files.
See Also
C++ Standard Library Reference
Thread Safety in the C++ Standard Library



