C++ 经常使用类 string类

===6.3.2使用string对象===

string word="I love China"
*链接字符串*
string description=adjective  + " " + word;
_Note_: 不能连接两个字符串字面量，以下的语句是错误的

string test= "I have" + "a dream";

===6.3.3訪问字符串中的字符===
*读取字符串*
getline(cin, text);
getline(cin, text, '#')_;

word[index];

===6.3.4訪问子字符串===
* substr(index0, length);
string phrase = "the higher the fewer";

string wold= phrase.substr(4,6 );

===6.3.5比較字符串===
*操作符*
> >= < !=
*compare()*
world.compare("end");

word.compare(2, 4, "end");

===6.3.6搜索字符串:find===
string sentence = "Manners maketh man";
int a= sentence.find("man");
int b= sentence.find("man", index);//从index開始搜索
假设没有找到。返回~~string:npos~~
*搜索字符集*
string separeators= " ,."";
sentence.find_first_of(separeators);
sentence.find_last_of(separeators);
sentence.find_last_not_of(separeators);
sentence.find_first_not_of(separeators);
*逆向搜索*

sentence.rfind("man");

===6.3.7改动字符串:insert、replace、erase===
*1.insert*
_`mystring.insert(index, anotherstring)`
sentence.insert(13, world, 8, 5);//从index=8開始之后的5个字符
把几个同样字符串插入到string对象中：sentence.insert(index,times, string);
*2.replace*
将从index開始的num个字符，替换成新的string：sentence.replace(index, num, string);
*3.erase*

删除从index開始的num个字符：sentence.erase(index, num);

===6.3.8注意事项===

1） append函数与char 和char*

append函数的原型例如以下：

string& append (const string& str);
	
string& append (const string& str, size_t subpos, size_t sublen);
	
string& append (const char* s);

string& append (const char* s, size_t n);
	
string& append (size_t n, char c);

注意。char* 和char用作append的參数时候。比如，想在string尾部添加一个字符，须要用mystring.append(1, ch) 而不是mystring.apend(ch). 相同。想将chars的当中一部分插入string中。须要用mystring.append(s+a, b-a)

注意，假设只想添加一个字符。使用push_back就可以

string 具体解释

1.*string constructor*

default (1) string();
copy (2) string (const string& str);
substring (3) string (const string& str, size_t pos, size_t len = npos);
from c-string (4) string (const char* s);
from buffer (5) string (const char* s, size_t n);
fill (6) string (size_t n, char c);
range (7) template <class InputIterator>
  string  (InputIterator first, InputIterator last);

// string constructor
#include <iostream>
#include <string>

int main ()
{
  std::string s0 ("Initial string");
  // constructors used in the same order as described above:
  std::string s1;
  std::string s2 (s0);
  std::string s3 (s0, 8, 3);
  std::string s4 ("A character sequence", 6);
  std::string s5 ("Another character sequence");
  std::string s6 (10, 'x');
  std::string s7a (10, 42);      // 42 is the ASCII code for '*'
  std::string s7b (s0.begin(), s0.begin()+7);
  std::cout << "s1: " << s1 << "
s2: " << s2 << "
s3: " << s3;
  std::cout << "
s4: " << s4 << "
s5: " << s5 << "
s6: " << s6;
  std::cout << "
s7a: " << s7a << "
s7b: " << s7b << '
';
  return 0;
}
**output**:
s1: 
s2: Initial string
s3: str
s4: A char
s5: Another character sequence
s6: xxxxxxxxxx
s7a: **********
s7b: Initial

2.迭代器：
begin();
end();


3.capacity:
size();
length();
clear();
empty();


4.Element Access:
operator[]
at()
back();
front();

5.Modifier
operator+=
append()
push_back()
assign()
insert()
erase()
replcace();
swap();
pop_back();

6.String Operations:
copy();
find();
find_first_of();
find_last_of();
find_first_not_of();
find_last_not_of();
substr();
compare();

7.Member constants:
npos


8.Non-member function overloads:
getline();