STL源码剖析 [简单应用总结二]
容器：
//see <a target=_blank href="http://www.cplusplus.com/reference/stl/">http://www.cplusplus.com/reference/stl/</a>
// 演示STL容器
#include <assert.h>
#include <vector>
#include <iostream>
#include <iterator>
#include <list>
#include <ext/slist>
#include <deque>
#include <set>
#include <map>
#include <ext/hash_set>
#include <ext/hash_map>
#include <stack>
#include <queue>
//用于排序的函数对象
struct ltstr
{
bool operator()(const char* s1, const char* s2) const
{
return strcmp(s1, s2) < 0;
}
};
//用于哈希查找的函数对象
struct eqstr
{
bool operator()(const char* s1, const char* s2) const
{
return strcmp(s1, s2) == 0;
}
};
//哈希查找
void lookup(const __gnu_cxx::hash_set<const char*, __gnu_cxx::hash<const char*>, eqstr>& Set,
const char* word)
{
__gnu_cxx::hash_set<const char*, __gnu_cxx::hash<const char*>, eqstr>::const_iterator it
= Set.find(word);
std::cout << word << ": "
<< (it != Set.end() ? "present" : "not present")
<< std::endl;
}
//哈希查找
void lookup(const __gnu_cxx::hash_multiset<const char*, __gnu_cxx::hash<const char*>, eqstr>& Set,
const char* word)
{
int n_found = Set.count(word);
std::cout << word << ": "
<< n_found << " "
<< (n_found == 1 ? "instance" : "instances")
<< std::endl;
}
// 使用typedef简化容器的类型名
typedef __gnu_cxx::hash_multimap<const char*, int, __gnu_cxx::hash<const char*>, eqstr> map_type;
//哈希查找
void lookup(const map_type& Map, const char* str)
{
std::cout << str << ": ";
std::pair<map_type::const_iterator, map_type::const_iterator> p =
Map.equal_range(str);
for (map_type::const_iterator i = p.first; i != p.second; ++i)
std::cout << (*i).second << " ";
std::cout << std::endl;
}
int main(int argc, const char *argv[])
{
{
//vector<T, Alloc>
//支持随机元素访问的动态数组（序列）
std::vector<int> V;
V.insert(V.begin(), 3);
assert(V.size() == 1 && V.capacity() >= 1 && V[0] == 3);
//扩大vector的容量到指定值，除非已经超过指定值
std::cout << "size:" << V.size() << ",capacity:" << V.capacity() << std::endl;
V.reserve(3);
std::cout << "size:" << V.size() << ",capacity:" << V.capacity() << std::endl;
//用构造函数复制vector，容量会自动压缩
std::vector<int> temp(V.begin(), V.end());
std::cout << "Use vector's ctor copy:" << std::endl;
std::cout << "size:" << temp.size() << ",capacity:" << temp.capacity() << std::endl;
//用swap把序列转移到新的vector，容量不会改变，
//而且原来的vector会被修改（交换了内容）
std::vector<int> temp_swap;
temp_swap.swap(V);
std::cout << "Use vector's swap:" << std::endl;
std::cout << "temp_swap's size:" << temp_swap.size() << ",capacity:" << temp_swap.capacity() << std::endl;
std::cout << "V's size:" << V.size() << ",capacity:" << V.capacity() << std::endl;
//把序列复制到vector，通常用于输入流
//用法类似std::copy
std::cout << "Please input double array (NaN is EOF):" << std::endl;
std::istream_iterator<double> first(std::cin);
std::istream_iterator<double> eof;
std::vector<double> buf(first, eof);
std::cout << "input double numbers are:" << std::endl;
std::copy(buf.begin(), buf.end(),
std::ostream_iterator<double>(std::cout, "\n"));
std::cout << std::flush;
}
{
//list<T, Alloc>
//双向链表
std::list<int> L;
L.push_back(0);
L.push_front(1);
L.insert(++L.begin(), 2);
std::cout << "list:" << std::endl;
std::copy(L.begin(), L.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
//排序
L.sort();
std::cout << "sorted list:" << std::endl;
std::copy(L.begin(), L.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
//合并
std::list<int> L2;
L2.push_back(3);
L2.push_back(2);
L2.push_back(1);
L.merge(L2);
std::cout << "merged list:" << std::endl;
std::copy(L.begin(), L.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
//颠倒次序
L.reverse();
std::cout << "reversed list:" << std::endl;
std::copy(L.begin(), L.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
}
{
//slist<T, Alloc>
//单向链表
//从begin()插入
__gnu_cxx::slist<int> L;
L.push_front(0);
L.push_front(1);
L.insert_after(L.begin(), 2);
std::cout << "slist, insert to begin:" << std::endl;
std::copy(L.begin(), L.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
//从end()插入
__gnu_cxx::slist<int>::iterator back = L.previous(L.end());
back = L.insert_after(back, 3);
back = L.insert_after(back, 4);
back = L.insert_after(back, 5);
std::cout << "slist, insert to end:" << std::endl;
std::copy(L.begin(), L.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
}
{
//deque<T, Alloc>
//双端队列，类似vector，
//支持随机访问和双端插入，
//但不支持capacity()和reserve()
std::deque<int> Q;
Q.push_back(3);
Q.push_front(1);
Q.insert(Q.begin() + 1, 2);
Q[2] = 0;
std::cout << "deque:" << std::endl;
std::copy(Q.begin(), Q.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
}
{
//set<Key, Compare, Alloc>
//集合，不重复的序列，可执行交、并、差集
const int N = 6;
const char* a[N] = {"isomer", "ephemeral", "prosaic",
"nugatory", "artichoke", "serif"};
const char* b[N] = {"flat", "this", "artichoke",
"frigate", "prosaic", "isomer"};
std::set<const char*, ltstr> A(a, a + N);
std::set<const char*, ltstr> B(b, b + N);
std::set<const char*, ltstr> C;
std::cout << "Set A: ";
std::copy(A.begin(), A.end(),
std::ostream_iterator<const char*>(std::cout, " "));
std::cout << std::endl;
std::cout << "Set B: ";
std::copy(B.begin(), B.end(),
std::ostream_iterator<const char*>(std::cout, " "));
std::cout << std::endl;
std::cout << "Union: ";
std::set_union(A.begin(), A.end(), B.begin(), B.end(),
std::ostream_iterator<const char*>(std::cout, " "),
ltstr());
std::cout << std::endl;
std::cout << "Intersection: ";
std::set_intersection(A.begin(), A.end(), B.begin(), B.end(),
std::ostream_iterator<const char*>(std::cout, " "),
ltstr());
std::cout << std::endl;
std::set_difference(A.begin(), A.end(), B.begin(), B.end(),
std::inserter(C, C.begin()),
ltstr());
std::cout << "Set C (difference of A and B): ";
std::copy(C.begin(), C.end(),
std::ostream_iterator<const char*>(std::cout, " "));
std::cout << std::endl;
}
{
//map<Key, Data, Compare, Alloc>
//关联数组，映射表，键不可重复
std::map<const char*, int, ltstr> months;
months["january"] = 31;
months["february"] = 28;
months["march"] = 31;
months["april"] = 30;
months["may"] = 31;
months["june"] = 30;
months["july"] = 31;
months["august"] = 31;
months["september"] = 30;
months["october"] = 31;
months["november"] = 30;
months["december"] = 31;
std::cout << "june -> " << months["june"] << std::endl;
std::map<const char*, int, ltstr>::iterator cur = months.find("june");
std::map<const char*, int, ltstr>::iterator prev = cur;
std::map<const char*, int, ltstr>::iterator next = cur;
++next;
--prev;
std::cout << "Previous (in alphabetical order) is " << (*prev).first << std::endl;
std::cout << "Next (in alphabetical order) is " << (*next).first << std::endl;
//另一种插入键值对的方法（可以判断是否插入成功）
std::map<const char*, int, ltstr> M;
std::pair<std::map<const char*, int>::iterator, bool> p = M.insert(std::make_pair("A", 17));
//第二返回值表示插入是否成功
if(p.second)
std::cout << "insert pair is " << p.first->first << ", " << p.first->second << std::endl;
//<< "pair:" << "," << p.second
}
{
//multiset<Key, Compare, Alloc>
//允许元素重复的集合
const int N = 10;
int a[N] = {4, 1, 1, 1, 1, 1, 0, 5, 1, 0};
int b[N] = {4, 4, 2, 4, 2, 4, 0, 1, 5, 5};
std::multiset<int> A(a, a + N);
std::multiset<int> B(b, b + N);
std::multiset<int> C;
std::cout << "Set A: ";
std::copy(A.begin(), A.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
std::cout << "Set B: ";
std::copy(B.begin(), B.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
std::cout << "Union: ";
std::set_union(A.begin(), A.end(), B.begin(), B.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
std::cout << "Intersection: ";
std::set_intersection(A.begin(), A.end(), B.begin(), B.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
std::set_difference(A.begin(), A.end(), B.begin(), B.end(),
std::inserter(C, C.begin()));
std::cout << "Set C (difference of A and B): ";
std::copy(C.begin(), C.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
}
{
//multimap<Key, Data, Compare, Alloc>
//键允许重复的关联数组
std::multimap<const char*, int, ltstr> m;
m.insert(std::pair<const char* const, int>("a", 1));
m.insert(std::pair<const char* const, int>("c", 2));
m.insert(std::pair<const char* const, int>("b", 3));
m.insert(std::pair<const char* const, int>("b", 4));
m.insert(std::pair<const char* const, int>("a", 5));
m.insert(std::pair<const char* const, int>("b", 6));
std::cout << "Number of elements with key a: " << m.count("a") << std::endl;
std::cout << "Number of elements with key b: " << m.count("b") << std::endl;
std::cout << "Number of elements with key c: " << m.count("c") << std::endl;
std::cout << "Elements in m: " << std::endl;
for (std::multimap<const char*, int, ltstr>::iterator it = m.begin(); it != m.end(); ++it)
std::cout << " [" << (*it).first << ", " << (*it).second << "]" << std::endl;
}
{
//hash_set<Key, HashFcn, EqualKey, Alloc>
//支持哈希查找的集合，不允许元素重复
__gnu_cxx::hash_set<const char*, __gnu_cxx::hash<const char*>, eqstr> Set;
Set.insert("kiwi");
Set.insert("plum");
Set.insert("apple");
Set.insert("mango");
Set.insert("apricot");
Set.insert("banana");
lookup(Set, "mango");
lookup(Set, "apple");
lookup(Set, "durian");
}
{
//hash_map<Key, Data, HashFcn, EqualKey, Alloc>
//支持哈希查找的关联数组，不允许键重复
__gnu_cxx::hash_map<const char*, int, __gnu_cxx::hash<const char*>, eqstr> months;
months["january"] = 31;
months["february"] = 28;
months["march"] = 31;
months["april"] = 30;
months["may"] = 31;
months["june"] = 30;
months["july"] = 31;
months["august"] = 31;
months["september"] = 30;
months["october"] = 31;
months["november"] = 30;
months["december"] = 31;
std::cout << "september -> " << months["september"] << std::endl;
std::cout << "april -> " << months["april"] << std::endl;
std::cout << "june -> " << months["june"] << std::endl;
std::cout << "november -> " << months["november"] << std::endl;
}
{
//hash_multiset<Key, HashFcn, EqualKey, Alloc>
//支持哈希查找的集合，允许元素重复
__gnu_cxx::hash_multiset<const char*, __gnu_cxx::hash<const char*>, eqstr> Set;
Set.insert("mango");
Set.insert("kiwi");
Set.insert("apple");
Set.insert("kiwi");
Set.insert("mango");
Set.insert("mango");
Set.insert("apricot");
Set.insert("banana");
Set.insert("mango");
lookup(Set, "mango");
lookup(Set, "apple");
lookup(Set, "durian");
}
{
//hash_multimap<Key, Data, HashFcn, EqualKey, Alloc>
//支持哈希查找的集合，允许键重复
map_type M;
M.insert(map_type::value_type("H", 1));
M.insert(map_type::value_type("H", 2));
M.insert(map_type::value_type("C", 12));
M.insert(map_type::value_type("C", 13));
M.insert(map_type::value_type("O", 16));
M.insert(map_type::value_type("O", 17));
M.insert(map_type::value_type("O", 18));
M.insert(map_type::value_type("I", 127));
lookup(M, "I");
lookup(M, "O");
lookup(M, "Rn");
}
{
//stack<T, Sequence>
//堆栈，后进先出
std::stack<int> S;
S.push(8);
S.push(7);
S.push(4);
assert(S.size() == 3);
assert(S.top() == 4);
S.pop();
assert(S.top() == 7);
S.pop();
assert(S.top() == 8);
S.pop();
assert(S.empty());
}
{
//queue<T, Sequence>
//队列，先进先出
std::queue<int> Q;
Q.push(8);
Q.push(7);
Q.push(6);
Q.push(2);
assert(Q.size() == 4);
assert(Q.back() == 2);
assert(Q.front() == 8);
Q.pop();
assert(Q.front() == 7);
Q.pop();
assert(Q.front() == 6);
Q.pop();
assert(Q.front() == 2);
Q.pop();
assert(Q.empty());
}
{
//priority_queue<T, Sequence, Compare>
//优先队列，最先弹出的是队列中的最大值
std::priority_queue<int> Q;
Q.push(1);
Q.push(4);
Q.push(2);
Q.push(8);
Q.push(5);
Q.push(7);
assert(Q.size() == 6);
assert(Q.top() == 8);
Q.pop();
assert(Q.top() == 7);
Q.pop();
assert(Q.top() == 5);
Q.pop();
assert(Q.top() == 4);
Q.pop();
assert(Q.top() == 2);
Q.pop();
assert(Q.top() == 1);
Q.pop();
assert(Q.empty());
//让队列中最小元素的先出列
//其中，模板的第二参数表示它的底层实现是std::vector<int>
std::priority_queue< int, std::vector<int>, std::greater<int> > Q2;
Q2.push(4);
Q2.push(2);
assert(Q2.top() == 2);
Q2.pop();
assert(Q2.top() == 4);
}
//标准C++允许main不返回，但标准C要求必须返回
return 0;
}
自定义分配器：
// 19.4.2 一个用户定义分配器
//演示标准库分配器allocator接口的简单实现
#include <cstddef>
#include <vector>
#include <iostream>
#include <iterator>
//class Pool定义一个简单接口的小内存块内存池
//这个内存池一次只能分配恒定大小的小内存块（由构造函数参数指定）
class Pool
{
private:
//用于分配和释放内存的链表
//比Chunk的粒度小，多个Link分割一个Chunk
//分配前Link的next域用于计算下一个分配位置
//分配后Link只是void*内存块的头部
struct Link
{
Link *next;
};
// 底层内存分配区的分区块
// 一个Pool内有多个依次链接的Chunk
//每个Chunk被多个Link分割成更小的内存块
//（但所有Link的排列次序不一定依照其所在Chunk块的排列次序），
//但因为内存是连续的，所以在增量分配和全体释放时速度会较快
struct Chunk
{
//让一个Chunk不超过8K且略小于8K
enum { SIZE = 8 * 1024 - 16 };
unsigned char mem[SIZE];
Chunk *next; //next应该不会超过16个字节
};
//多个Chunk前后组成一个链表（好像一个栈）
Chunk *chunks;
//每次alloc()返回的内存块最大大小，
//但不能比sizeof(Link)小，也不能比Chunk::SIZE大
const unsigned int esize;
//当前空闲Chunk块内的空闲Link头部
Link *head;
//禁用默认的复制构造函数和复制赋值，
//所以这里不需要定义方法体
private:
Pool(Pool& sz);
void operator=(Pool&);
private:
void grow();
public:
Pool(unsigned int n);//指定每次alloc()返回的内存块大小
~Pool();
void* alloc(); //不需要指定内存块大小（在构造函数中指定）
void free(void* b);
};
//从head链表的头部取出一个Link
//如果空闲Chunk块用完，需要分配新的Chunk块，
//然后用Link链表分割这个新的空闲Chunk块。
inline void* Pool::alloc()
{
if (head == 0)
{
grow();
}
Link *p = head;
head = p->next;
std::cout << "Pool::alloc(): p == " << p << ", head == " << head << std::endl;
return p;
}
//把要释放的b放回head链表的头部
inline void Pool::free(void* b)
{
Link* p = static_cast<Link*>(b);
p->next = head;
std::cout << "Pool::free(): p == " << p << ", head == " << head << std::endl;
head = p;
}
Pool::Pool(unsigned int sz)
: esize(sz < sizeof(Link) ? sizeof(Link) : sz)
{
head = 0;
chunks = 0;
}
Pool::~Pool()
{
Chunk *n = chunks;
while (n)
{
Chunk *p = n;
n = n->next;
delete p;
}
}
//增量分配内存
//虽然Link*所在的小内存块是连续的，
//但alloc的分配次序不一定是连续的
//（因为free()可能放回旧的内存块）
void Pool::grow()
{
Chunk *n = new Chunk();
n->next = chunks;
chunks = n;
std::cout << "Pool::grow(): esize == " << esize << std::endl;
const int nelem = Chunk::SIZE / esize;
unsigned char *start = n->mem;
unsigned char *last = &start[(nelem - 1) * esize];
for (unsigned char *p = start; p < last; p += esize)
{
reinterpret_cast<Link*>(p)->next = reinterpret_cast<Link*>(p + esize);
}
reinterpret_cast<Link*>(last)->next = 0; //见alloc()的if (head == 0)
head = reinterpret_cast<Link*>(start);
}
//template Pool_alloc把class Pool适配到C++标准库的分配器接口
//不完整，因为有些接口没有实现，而有些接口只实现部分功能
template<class T>
class Pool_alloc
{
private:
static Pool mem; //全局，以提高效率
public:
typedef T value_type;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
typedef T *pointer;
typedef const T *const_pointer;
typedef T &reference;
typedef const T&const_reference;
Pool_alloc();
T* allocate(size_type n, void*);
void deallocate(pointer p, size_type n);
};
//构造静态的mem域
//因为Pool只能分配固定大小的小内存块，
//而且Pool_alloc没有实现rebind方法
//所以这里指定每次分配的连续内存区都必须是sizeof(T) * 128，
//虽然造成浪费，但确保分配的内存是连续的。
//没有超过Chunk块的8K上限，所以是安全的。
template <class T>
Pool Pool_alloc<T>::mem(sizeof(T) * 128);
template <class T>
Pool_alloc<T>::Pool_alloc()
{
}
template<class T>
T* Pool_alloc<T>::allocate(size_type n, void* = 0)
{
if (n <= 128)
{
void *p = mem.alloc();
std::cout << "allocate : " << n << ", " << p << std::endl;
return static_cast<T*>(p);
} else {
//TODO:
std::cout << "allocate : " << n << std::endl;
throw "allocate error"; //出错
}
}
template<class T>
void Pool_alloc<T>::deallocate(pointer p, size_type n)
{
if (n <= 128)
{
std::cout << "deallocate : " << n << ", " << p << std::endl;
mem.free(p);
return;
} else {
//TODO:
std::cout << "deallocate : " << n << std::endl;
throw "deallocate error"; //出错
}
}
int main(int argc, const char *argv[])
{
{
std::vector<int> V1;
V1.push_back(1);
V1.push_back(2);
V1.push_back(3);
V1.push_back(4);
std::cout << "V1:"<< std::endl;
std::copy(V1.begin(), V1.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
}
{
std::cout << "==================="<< std::endl;
try
{
std::vector< int, Pool_alloc<int> > V2;
std::cout << "V2.push_back(1);" << std::endl;
V2.push_back(1);
std::cout << "V2.push_back(2);" << std::endl;
V2.push_back(2);
std::cout << "V2.push_back(3);" << std::endl;
V2.push_back(3);
V2.push_back(4);
std::cout << "V2:"<< std::endl;
std::copy(V2.begin(), V2.end(),
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
}
catch (const char *&str)
{
std::cout << str << std::endl;
}
}
return 0;
}
/**
运行结果：
V1:
1 2 3 4
===================
V2.push_back(1);
Pool::grow(): esize == 512
Pool::alloc(): p == 0x3e4d68, head == 0x3e4f68
allocate : 1, 0x3e4d68
V2.push_back(2);
Pool::alloc(): p == 0x3e4f68, head == 0x3e5168
allocate : 2, 0x3e4f68
deallocate : 1, 0x3e4d68
Pool::free(): p == 0x3e4d68, head == 0x3e5168
V2.push_back(3);
Pool::alloc(): p == 0x3e4d68, head == 0x3e5168
allocate : 4, 0x3e4d68
deallocate : 2, 0x3e4f68
Pool::free(): p == 0x3e4f68, head == 0x3e5168
V2:
1 2 3 4
deallocate : 4, 0x3e4d68
Pool::free(): p == 0x3e4d68, head == 0x3e4f68
*/