底层数组的指针
T* data() noexcept; //(C++11 起)
const T* data() const noexcept; //(C++11 起)
返回指向作为元素存储工作的底层数组的指针。指针满足范围 [data(); data() + size()) 始终是合法范围，即使容器为空（该情况下 data() 不可解引用）。
参数 （无）
返回值 指向底层元素存储的指针。对于非空容器，返回的指针与首元素地址比较相等。
复杂度 常数。
注意 若 size() 为 0 ，则 data() 可能或可能不返回空指针。
用例
std::vector<std::string> words {
"I", "am", "the", "most", "handsome", "programmer"};
for(auto it = words.data(); it != words.data() + words.size(); it ++)
{
cout << *it << " ";
}
容器擦除所有元素
void clear(); (C++11 前)
void clear() noexcept; (C++11 起)
从容器擦除所有元素。此调用后 size() 返回零。
非法化任何指代所含元素的引用、指针或迭代器。任何尾后迭代器亦被非法化。
保持 vector 的 capacity() 不变（注意：更改容量上的标准限制在 vector::reserve 的规定中，见 [1] ）。
参数 （无）
返回值 （无）
复杂度 与容器大小，即元素数成线性。
检查容器是否无元素
bool empty() const; (C++11 前)
bool empty() const noexcept; (C++11 起)
检查容器是否无元素，即是否 begin() == end() 。
参数 （无）
返回值 若容器为空则为 true ，否则为 false
复杂度 常数。
用例
std::vector<std::string> words1 {
"I", "am", "the", "most", "handsome", "programmer"};
if(words1.empty())
{
cout << "words1 is empty!" << endl;
}
else
{
cout << "words1 is not empty!" << endl;
}
words1.clear();
if(words1.empty())
{
cout << "words1 is empty!" << endl;
}
else
{
cout << "words1 is not empty!" << endl;
}
std::vector<std::string> words2;
if(words2.empty())
{
cout << "words2 is empty!" << endl;
}
else
{
cout << "words2 is not empty!" << endl;
}
cout << endl;
容器擦除指定的元素
iterator erase( iterator pos ); (C++11 前)
iterator erase( const_iterator pos ); (C++11 起)
iterator erase( iterator first, iterator last ); (C++11 前)
iterator erase( const_iterator first, const_iterator last ); (C++11 起)
从容器擦除指定的元素。
- 移除位于 pos 的元素。
- 移除范围 [first; last) 中的元素。
非法化位于擦除点或之后的迭代器，包含 end() 迭代器。
迭代器 pos 必须合法且可解引用。从而不能以 end() 迭代器（合法，但不可解引用）为 pos 的值。
若 first==last 则迭代器 first 不必可解引用：擦除空范围是无操作。
参数
pos - 指向要移除的元素的迭代器
first, last - 要移除的元素范围
类型要求 T 必须满足可移动赋值 (MoveAssignable) 的要求。
返回值 后随最后被移除元素的迭代器。若迭代器 pos 指代最后元素，则返回 end() 迭代器。
异常 不抛出，除非 T 的赋值运算符抛异常。
复杂度
线性：调用 T 析构函数的次数与被擦除的元素数相同，调用 T 赋值运算符的次数与 vector 中被擦除元素后的元素数相等。
用例
std::vector<std::string> words {
"I", "am", "the", "most", "handsome", "programmer"};
printVector("words : ", words);
//删除偏移量为3的元素
words.erase(words.begin() + 3);
printVector("words erase: ", words);
// 范围删除，删除偏移量为3至末尾的元素
words.erase(words.begin() + 3, words.end());
printVector("words erase range: ", words);
根据系统或库实现限制的容器可保有的元素最大数量
size_type max_size() const; (C++11 前)
size_type max_size() const noexcept; (C++11 起)
返回根据系统或库实现限制的容器可保有的元素最大数量，即对于最大容器的 std::distance(begin(), end()) 。
参数 （无）
返回值 元素数量的最大值。
复杂度 常数。
注意
此值通常反映容器大小上的理论极限，至多为 std::numeric_limits<difference_type>::max() 。运行时，可用 RAM 总量可能会限制容器大小到小于 max_size() 的值。
用例
std::vector<std::string> words {
"I", "am", "the", "most", "handsome", "programmer"};
cout << "vector<std::string> max_size: " << words.max_size() << std::endl;
std::vector<int> words1;
cout << "vector<int> max_size: " << words1.max_size() << std::endl;
交换容器内容
void swap( vector& other ); (C++17 前)
void swap( vector& other ) noexcept(/* see below */); (C++17 起)
将内容与 other 的交换。不在单个元素上调用任何移动、复制或交换操作。
所有迭代器和引用保持合法。尾后迭代器被非法化。
若 std::allocator_traits<allocator_type>::propagate_on_container_swap::value 为 true ，则用非成员 swap 的非限定调用交换分配器。否则，不交换它们（且若 get_allocator() != other.get_allocator() ，则行为未定义）。 (C++11 起)
参数 other - 要与之交换内容的容器
返回值 （无）
异常 （无） (C++17 前)
noexcept 规定：
noexcept(std::allocator_traits::propagate_on_container_swap::value
|| std::allocator_traits::is_always_equal::value) (C++17 起)
复杂度 常数。
template< class T, class Alloc >
void swap( vector<T,Alloc>& lhs, vector<T,Alloc>& rhs ); (C++17 前)
template< class T, class Alloc >
void swap( vector<T,Alloc>& lhs, vector<T,Alloc>& rhs ) noexcept(/* see below */); (C++17 起)
为 std::vector 特化 std::swap 算法。交换 lhs 与 rhs 的内容。调用 lhs.swap(rhs) 。
参数 lhs, rhs - 要交换内容的容器
返回值 （无）
复杂度 常数。
异常 noexcept 规定：
noexcept(noexcept(lhs.swap(rhs))) (C++17 起)
用例:
std::vector<std::string> words1 {
"I", "am", "the", "most", "handsome", "programmer"};
std::vector<std::string> words2 {
"handsome"};
printVector("words1: ", words1);
printVector("words2: ", words2);
words1.swap(words2);
printVector("words1 swap: ", words1);
printVector("words2 swap: ", words2);
std::swap(words1, words2);
printVector("words1 swap 2nd: ", words1);
printVector("words2 swap 2nd: ", words2);
代码汇总:
#include <vector>
#include <iostream>
using namespace std;
template<typename T>
void printVector(const string &name, const std::vector<T>& vec)
{
std::cout << name << " : " ;
for(auto &a :vec)
{
std::cout << a << " ";
}
std::cout << endl;
}
// 构造函数
void structure()
{
std::cout << "structure start" << endl;
// c++11 初始化器列表语法：
std::vector<std::string> words1 {
"I", "am", "the", "most", "handsome", "programmer"};
printVector("words1", words1);
// 构造拥有范围 [first, last) 内容的容器
// words2 = words1
std::vector<std::string> words2(words1.begin(), words1.end());
printVector("words2", words2);
// 拷贝构造 words3 = words1
std::vector<std::string> words3(words1);
printVector("words3", words3);
// 构造拥有 count 个有值 value 的元素的容器
// words4 为 {"handsome", "handsome", "handsome", "handsome", "handsome"}
std::vector<std::string> words4(5, "handsome");
printVector("words4", words4);
// 赋值构造
std::vector<std::string> words5 = words3;
printVector("words5", words5);
std::cout << "structure end" << endl << endl;
}
void assign()
{
std::cout << "assign start" << endl;
// 以 count 份 value 的副本替换内容。
std::vector<std::string> words1 {
"I", "am", "the", "most", "handsome", "programmer"};
printVector("words1_f", words1);
words1.assign(5, "handsome");
printVector("words1_s", words1);
//以范围 [first, last) 中元素的副本替换内容。若任一参数是指向 *this 中的迭代器则行为未定义
std::vector<std::string> words2;
words2.assign(words1.begin(), words1.end());
printVector("words2", words1);
std::cout << "assign end" << endl << endl;
}
void at()
{
std::cout << "at start" << endl;
std::vector<std::string> words1 {
"I", "am", "the", "most", "handsome", "programmer"};
size_t size = words1.size();
std::cout << "words1: ";
for(size_t i = 0; i < size; i++)
{
std::cout << words1.at(i) << " ";
}
std::cout << endl;
std::cout << "words1: ";
for(size_t i = 0; i < size; i++)
{
std::cout << words1[i] << " ";
}
std::cout << endl;
std::cout << "at end" << endl << endl;
}
void front_back()
{
std::cout << "front_back start " << endl;
std::vector<std::string> words1 {
"I", "am", "the", "most", "handsome", "programmer"};
// 返回到容器首元素的引用
std::cout << "words1: " << "front() : " << words1.front() << endl;
// 修改值
words1.front() = "you";
std::cout << "words1: " << "front() : " << words1.front() << endl;
// 返回到容器中最后一个元素的引用
std::cout << "words1: " << "back() : " << words1.back() << endl;
words1.back() = "human";
std::cout << "words1: " << "back() : " << words1.back() << endl;
std::cout << "front_back end" << endl << endl;
}
void MYiterator()
{
std::cout << "MYiterator start " << endl;
std::vector<std::string> words1 {
"I", "am", "the", "most", "handsome", "programmer"};
for(std::vector<std::string>::const_iterator it = words1.cbegin(); it != words1.cend(); it ++)
{
std::cout << *it << " ";
}
std::cout << std::endl;
for(std::vector<std::string>::const_reverse_iterator it = words1.crbegin(); it != words1.crend(); it ++)
{
std::cout << *it << " ";
}
std::cout << std::endl;
std::cout << "MYiterator end" << endl << endl;
}
void capacity_size()
{
std::cout << "capacity_size start " << endl;
std::vector<std::string> words {
"I", "am", "the", "most", "handsome", "programmer"};
std::cout << "words :" << "capacity(): " << words.capacity() << std::endl;
std::cout << "wordswordswords :" << "size(): " << words.size() << std::endl;
words.push_back("GGX");
std::cout << "words :" << "capacity(): " << words.capacity() << std::endl;
std::cout << "words :" << "size(): " << words.size() << std::endl;
//请求移除未使用的容量
words.shrink_to_fit();
std::cout << "words1 :" << "capacity(): " << words.capacity() << std::endl;
std::cout << "words1 :" << "size(): " << words.size() << std::endl;
std::cout << "capacity_size end" << endl << endl;
}
void MYResize()
{
std::cout << "MYResize start " << endl;
std::vector<std::string> words {
"I", "am", "the", "most", "handsome", "programmer"};
printVector("words : ", words);
//若当前大小大于 count ，则减小容器为其首 count 个元素。
std::vector<std::string> words1(words);
std::cout << "words1 size : " << words1.size() << std::endl;
words1.resize(words1.size() -1);
std::cout << "words1 resize : " << words1.size() <<std::endl;
printVector("words resize after: ", words1);
// 若当前大小小于 count ，则后附额外元素，并以 value 的副本初始化
std::vector<std::string> words2(words);
std::cout << "words2 size : " << words2.size() << std::endl;
words2.resize(words2.size() + 1, "handsome");
std::cout << "words2 resize : " << words2.size() <<std::endl;
printVector("words resize after: ", words2);
std::cout << "MYResize end" << endl << endl;
}
void myData()
{
std::cout << "myData start " << endl;
std::vector<std::string> words {
"I", "am", "the", "most", "handsome", "programmer"};
for(auto it = words.data(); it != words.data() + words.size(); it ++)
{
cout << *it << " ";
}
cout << endl;
std::cout << "myData end" << endl << endl;
}
void empty_clear()
{
std::cout << "empty_clear start " << endl;
std::vector<std::string> words1 {
"I", "am", "the", "most", "handsome", "programmer"};
if(words1.empty())
{
cout << "words1 is empty!" << endl;
}
else
{
cout << "words1 is not empty!" << endl;
}
words1.clear();
if(words1.empty())
{
cout << "words1 is empty!" << endl;
}
else
{
cout << "words1 is not empty!" << endl;
}
std::vector<std::string> words2;
if(words2.empty())
{
cout << "words2 is empty!" << endl;
}
else
{
cout << "words2 is not empty!" << endl;
}
cout << endl;
std::cout << "empty_clear end" << endl << endl;
}
void myerase()
{
std::cout << "myerase start " << endl;
std::vector<std::string> words {
"I", "am", "the", "most", "handsome", "programmer"};
printVector("words : ", words);
//删除偏移量为3的元素
words.erase(words.begin() + 3);
printVector("words erase: ", words);
// 范围删除，删除偏移量为3至末尾的元素
words.erase(words.begin() + 3, words.end());
printVector("words erase range: ", words);
std::cout << "myerase end" << endl << endl;
}
void max_size()
{
std::cout << "max_size start " << endl;
std::vector<std::string> words {
"I", "am", "the", "most", "handsome", "programmer"};
cout << "vector<std::string> max_size: " << words.max_size() << std::endl;
std::vector<int> words1;
cout << "vector<int> max_size: " << words1.max_size() << std::endl;
std::cout << "max_size end" << endl << endl;
}
void mySwap()
{
std::cout << "mySwap start " << endl;
std::vector<std::string> words1 {
"I", "am", "the", "most", "handsome", "programmer"};
std::vector<std::string> words2 {
"handsome"};
printVector("words1: ", words1);
printVector("words2: ", words2);
words1.swap(words2);
printVector("words1 swap: ", words1);
printVector("words2 swap: ", words2);
std::swap(words1, words2);
printVector("words1 swap 2nd: ", words1);
printVector("words2 swap 2nd: ", words2);
std::cout << "mySwap end" << endl << endl;
}
int main( )
{
// structure();
// assign();
// at();
// front_back();
// MYiterator();
// capacity_size();
// MYResize();
myData();
myerase();
max_size();
mySwap();
return 0;
}
