Книга: Standard Template Library Programmer

set

set<Key, Compare, Alloc>

Category: containers

Component type: type

Set is a Sorted Associative Container that stores objects of type Key. Set is a Simple Associative Container, meaning that its value type, as well as its key type, is Key. It is also a Unique Associative Container, meaning that no two elements are the same.

Set and multiset are particularly well suited to the set algorithms includes, set_union, set_intersection, set_difference, and set_symmetric_difference. The reason for this is twofold. First, the set algorithms require their arguments to be sorted ranges, and, since set and multiset are Sorted Associative Containers, their elements are always sorted in ascending order. Second, the output range of these algorithms is always sorted, and inserting a sorted range into a set or multiset is a fast operation: the Unique Sorted Associative Container and Multiple Sorted Associative Container requirements guarantee that inserting a range takes only linear time if the range is already sorted.

Set has the important property that inserting a new element into a set does not invalidate iterators that point to existing elements. Erasing an element from a set also does not invalidate any iterators, except, of course, for iterators that actually point to the element that is being erased.

struct ltstr {
 bool operator()(const char* s1, const char* s2) const {
  return strcmp(s1, s2) < 0;
 }
};
int main() {
 const int N = 6;
 const char* a[N] = {"isomer", "ephemeral", "prosaic", "nugatory", "artichoke", "serif"};
 const char* b[N] = {"flat", "this", "artichoke", "frigate", "prosaic", "isomer"};
 set<const char*, ltstr> A(a, a + N);
 set<const char*, ltstr> B(b, b + N);
 set<const char*, ltstr> C;
 cout << "Set A: ";
 copy(A.begin(), A.end(), ostream_iterator<const char*>(cout, " "));
 cout << endl;
 cout << "Set B: ";
 copy(B.begin(), B.end(), ostream_iterator<const char*>(cout, " "));
 cout << endl;
 cout << "Union: ";
 set_union(A.begin(), A.end(), B.begin(), B.end(), ostream_iterator<const char*>(cout, " "), ltstr());
 cout << endl;
 cout << "Intersection: ";
 set_intersection(A.begin(), A.end(), B.begin(), B.end(), ostream_iterator<const char*>(cout, " "), ltstr());
 cout << endl;
 set_difference(A.begin(), A.end(), B.begin(), B.end(), inserter(C, C.begin()), ltstr());
 cout << "Set C (difference of A and B): ";
 copy(C.begin(), C.end(), ostream_iterator <const char*>(cout, " "));
 cout << endl;
}

Defined in the standard header set, and in the nonstandard backward-compatibility header set.h.

Unique Sorted Associative Container, Simple Associative Container

• Key is Assignable.

• Compare is a Strict Weak Ordering whose argument type is Key.

• Alloc is an Allocator.

None.

All of set 's members are defined in the Unique Sorted Associative Container and Simple Associative Container requirements. Set does not introduce any new members.

[1] This member function relies on member template functions, which at present (early 1998) are not supported by all compilers. If your compiler supports member templates, you can call this function with any type of input iterator. If your compiler does not yet support member templates, though, then the arguments must either be of type const value_type* or of type set::const_iterator.

Associative Container, Sorted Associative Container, Simple Associative Container, Unique Sorted Associative Container, map, multiset, multimap, hash_set, hash_map, hash_multiset, hash_multimap

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