目录
[1.Member functions](#1.Member functions)
0.size(),capacity(),max_size(),length()
[1.扩容机制（vs和Linux g++对比）](#1.扩容机制（vs和Linux g++对比）)
[4.Element access:](#4.Element access:)
[6.String operations](#6.String operations)
学库一定会看文档
下面推荐个网站
cplusplus.com
https://cplusplus.com/
std::string
Strings are objects that represent sequences of characters.
strings 是表示字符序列的对象。
1.Member functions
string介绍
| default (1) | string(); |
| copy (2) | string (const string& str); |
| substring (3) | string (const string& str, size_t pos, size_t len = npos); 复制从字符位置pos开始并跨越len个字符的str部分（或者直到str的结尾，如果str太短或len为string::npos 
|
| from c-string (4) | string (const char* s); 复制由指针s指向的以空字符结尾的字符序列（C字符串） |
| from sequence (5) | string (const char* s, size_t n); 从指向s的字符数组中复制前n个字符 |
| fill (6) | string (size_t n, char c); |
| range (7) | template <class InputIterator> string (InputIterator first, InputIterator last); （先不看） |
|---|
cpp
void teststring()
{
string s0;
string s1("hello world");
string s2(s1);
string s3(s1, 5, 3);
string s4(s1, 5, 10);
string s5(s1, 5);
cout << "s0" << s0 << endl;
cout << "s1" << s1 << endl;
cout << "s2" << s2 << endl;
cout << "s3" << s3 << endl;
cout << "s4" << s4 << endl;
cout << "s5" << s5 << endl;
string s6(10, '#');
cout << s6 << endl;
s0 = s6;
cout << s0;
}
2.迭代器iterator
1.正向迭代器
关键：begin()
end()
cpp
void stringtest()
{
string s1("hello lInux");
string::iterator it1 = s1.begin();
while (it1 != s1.end())
{
cout << *it1 << " ";
++it1;
}
}
迭代器遍历vector
cpp
vector<int> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
vector<int>::iterator it2 = v.begin();
while (it2 != v.end())
{
cout << *it2;
it2++;
}范围for
cpp
for (auto e : s1)
{
cout << e;
}
cout << endl;
for (auto e : v)
{
cout << e;
}
cout << endl;2.反向迭代器
reverse_iterator
rbegin()
rend()
cpp
//反向迭代器
void stringtest1()
{
string s1("hello world !");
string::reverse_iterator rit = s1.rbegin();
while (rit != s1.rend())
{
cout << *rit << " ";
++rit;
}
}
特别注意：底层不是这样的！！！！！！！！！！！！
3.反向const
cpp
void stringtest1()
{
const string s1("hello world !");
string::const_reverse_iterator rit = s1.rbegin();
while (rit != s1.rend())
{
cout << *rit << " ";
++rit;
}
}4.反向const
cpp
void stringtest1()
{
const string s1("hello world !");
string::const_iterator rit = s1.begin();
while (rit != s1.end())
{
cout << *rit << " ";
++rit;
}
}3.容量capacity
0.size(),capacity(),max_size(),length()
cpp
//string s1("hello world!");
//cout << s1.size() << endl;
//cout << s1.length() << endl;
//cout << s1.max_size() << endl;
//cout << s1.capacity() << endl;1.扩容机制（vs和Linux g++对比）
cpp
int i = 0;
for (i = 0; i < 100; i++)
{
s.push_back('c');
if (sz != s.capacity())
{
sz = s.capacity();
cout << "capacity changed : " << sz << '\n';
}
}g++下面的 （2倍扩容）
vs下面的（除了第一个其他都是1.5倍扩容）
2.clear（）
cpp
string s1("hello world!");
cout << s1 << endl;
cout << s1.capacity() << endl;
s1.clear();
cout << s1 << endl;
cout << s1.capacity() << endl;
clear只清数据，不清空间
capacity 没有变化
2.1缩容shrink_to_fit（）
3.reserve(扩容)
s.reserve(100);
Linux下面
vs下面
总结：reserve只有比capacity大才起作用
4.resize()
10 删除 <size
20 插入 size < n < capacity
40 扩容+插入 capacity < n
cpp
void stringtest4()
{
string s1("hello world !!!");
cout << s1.size() << endl;
cout << s1.capacity() << endl;
s1.resize(10);
cout << s1.size() << endl;
cout << s1.capacity() << endl <<endl;
s1.resize(20);
cout << s1.size() << endl;
cout << s1.capacity() << endl << endl;
s1.resize(100,'x');
cout << s1.size() << endl;
cout << s1.capacity() << endl << endl;
}4.Element access:
string::operator[]
1.捕获某个字符
（1）[]
（2）at()
2.取头尾字符
cpp
void test1()
{
string s1("helloworld!");
cout << s1[5] << endl;
cout << s1.at(5) << endl;
cout << s1.front() << endl;
cout << s1.back() << endl;
}5.Modifiers
1.push_back（字符）
void push_back (char c);
2.append（字符串）
| string (1) | string& append (const string& str); |
| substring (2) | string& append (const string& str, size_t subpos, size_t sublen); |
| c-string (3) | string& append (const char* s); |
| buffer (4) | string& append (const char* s, size_t n); |
| fill (5) | string& append (size_t n, char c); |
| range (6) | template <class InputIterator> string& append (InputIterator first, InputIterator last); |
|---|
cpp
void test2()
{
string s1("hello world");
s1.push_back('!');
cout << s1 << endl;
s1.append("hwh");
cout << s1 << endl;
s1.append(10, 'x');
cout << s1 << endl;
string s2(" apple ");
//s1.append(s2);
//cout << s1 << endl;
s1.append(++s2.begin(),--s2.end()); //不想要空格
cout << s1 << endl;
}3.operator+=
| string (1) | string& operator+= (const string& str); |
| c-string (2) | string& operator+= (const char* s); |
| character (3) | string& operator+= (char c); |
|---|
4.assign（基本用不着）
| string (1) | string& assign (const string& str); |
| substring (2) | string& assign (const string& str, size_t subpos, size_t sublen); |
| c-string (3) | string& assign (const char* s); |
| buffer (4) | string& assign (const char* s, size_t n); |
| fill (5) | string& assign (size_t n, char c); |
| range (6) | template <class InputIterator> string& assign (InputIterator first, InputIterator last); |
|---|
5.insert
| string (1) | string& insert (size_t pos, const string& str); |
| substring (2) | string& insert (size_t pos, const string& str, size_t subpos, size_t sublen); |
| c-string (3) | string& insert (size_t pos, const char* s); |
| buffer (4) | string& insert (size_t pos, const char* s, size_t n); |
| fill (5) | string& insert (size_t pos, size_t n, char c); void insert (iterator p, size_t n, char c); |
| single character (6) | iterator insert (iterator p, char c); |
| range (7) | template <class InputIterator> void insert (iterator p, InputIterator first, InputIterator last); |
|---|
6.erase
| sequence (1) | string& erase (size_t pos = 0, size_t len = npos); |
| character (2) | iterator erase (iterator p); |
| range (3) | iterator erase (iterator first, iterator last); |
|---|
7.replace
| string (1) | string& replace (size_t pos, size_t len, const string& str); string& replace (iterator i1, iterator i2, const string& str); |
| substring (2) | string& replace (size_t pos, size_t len, const string& str, size_t subpos, size_t sublen); |
| c-string (3) | string& replace (size_t pos, size_t len, const char* s); string& replace (iterator i1, iterator i2, const char* s); |
| buffer (4) | string& replace (size_t pos, size_t len, const char* s, size_t n); string& replace (iterator i1, iterator i2, const char* s, size_t n); |
| fill (5) | string& replace (size_t pos, size_t len, size_t n, char c); string& replace (iterator i1, iterator i2, size_t n, char c); |
| range (6) | template <class InputIterator> string& replace (iterator i1, iterator i2, InputIterator first, InputIterator last); |
|---|
cpp
void test5()
{
string s1("hello hello hello hello hello");
size_t pos = s1.find(' ');
while (pos != string::npos)
{
s1.replace(pos, 1, "%20");
pos = s1.find(' ');
}
cout << s1 << endl;
}
另一种玩法：
cpp
void test6()
{
string s3;
string s2("hello hello hello hello hello");
s3.reserve(s2.size());
for (auto ch : s2)
{
if (ch != ' ')
{
s3 += ch;
}
else
{
s3 += "%20";
}
}
cout << s3 << endl;
s2.swap(s3);
}8.pop_back（c++11）
6.String operations
重点find
| string (1) | size_t find (const string& str, size_t pos = 0) const; |
| c-string (2) | size_t find (const char* s, size_t pos = 0) const; |
| buffer (3) | size_t find (const char* s, size_t pos, size_t n) const; |
| character (4) | size_t find (char c, size_t pos = 0) const; |
|---|
反着找
cpp
void teststring14()
{
string protocol, domain, uri;
string s1("https://legacy.cplusplus.com/reference/string/string/find/");
size_t pos = s1.find(':');
cout << pos << endl;
if (pos != string::npos);
{
protocol = s1.substr(0, (pos - 0)); //协议
cout << protocol << endl;
}
size_t pos1 = s1.find('/',pos+3);
if (pos1 != string::npos);
{
domain = s1.substr(pos + 3, pos1-(pos + 3));
cout << domain << endl;
uri = s1.substr(pos1 + 1);
cout << uri << endl;
}
}