C++语法基础--标准库类型--string(2)

绝地灬酷狼 2022-10-02 03:53 213阅读 0赞

**1.从标准输入读取string  
\*忽略开头所有的空白字符（空格，换行符，制表符）  
\*直至再次遇到空白符，读取终止  
 eg:  
string s;  
cin>>s;  //假设输入" hello "  
 cout<<s;  //输出hello（注意，开头和结尾并没有空格）  
  
  
2.getline  
原型：  
(1） istream& getline (istream& is, string& str, char delim); //遇到分割符后文件结束符才停止读取  
 (2) istream& getline (istream& is, string& str);  //正常读取模式  
 eg:  
string s;  
getline(cin,s,',');  //假设输入hello how,are you  
 cout<<s;  //输出hello how  
注：  
\*getline和string类型的输入对空白符的处理区别：getline不会忽略行开头的空白符，读取字符直至遇到换行符，读取终止并丢弃换行符  
 eg:  
int main()  
\{  
string str1;  
int count=0;  
while(cin>>str1) //一次性输入"hello how are you  
\{   
\++count;  
cout<<count<<": "<<str1<<'\\t';  //输出1：hello 2:how 3:are 4:you 可见每遇到一处空白符count就加1  
  
  
\}  
  
  
  
return 0;  
\}  
  
  
eg:  
int main()  
\{  
string str;  
  
  
getline(cin,str);//输入" hello how are you";注意前面的空白符，引号并不在包含在内，下同  
cout<<str<<endl;//输出" hello how are you"  
return 0;  
 \}  
  
  
  
3.stirng类的常用方法  
\*size；  
原型：  
size\_t size() const; //size\_t is the type returned by the sizeof operator   
 eg:  
int main ()  
\{  
std::string str ("hello");  
std::cout << "The size of str is:" << str.size(); //The size of str is:5  
 return 0;  
 \}  
  
  
\*empty:  
 原型：  
bool empty() const;  
 eg:  
int main ()  
\{  
std::string str;  
if(str.empty())  
\{  
std::cout << "The str is empty." ; //The str is empty.  
 \}  
 return 0;  
 \}  
  
  
4.成员类型  
\*size\_type:  
string类的配套类型，它在不同的机器上，长度是可以不同的，并非固定的长度，事实上许多库类型都定义了一些配 套类型  
 eg:  
int main ()  
\{  
string str("hello");  
string::size\_type len=str.size();  
cout<<len; //5  
 return 0;  
 \}  
  
  
5.关系操作符（非成员函数）:  
按字典顺序比较两个字符串  
\+，==,!=,<,>,<=,>=  
 eg:  
int main()  
\{  
string str1("hello");  
string str2("nihao");  
cout<<(str1>str2)<<endl; //0  
cout<<(str1==str2)<<endl;//0  
cout<<(str1!=str2)<<endl;//1  
cout<<(str1<str2)<<endl; //1  
cout<<(str1<=str2)<<endl; //1  
cout<<(str1>=str2)<<endl; //0  
return 0;  
 \}  
  
6.string对象的赋值  
operator=:  
 原型：  
basic\_string& operator=( const basic\_string& str );  
basic\_string& operator=( const CharT\* s );  
basic\_string& operator=( CharT ch )  
 eg:  
int main()  
\{  
string str1("nihao");  
string str2("hello");  
str1=str2;  
cout<<str1<<endl;//hello  
 str1="tanks";  
 cout<<str1<<endl;//thanks  
 str1='A';  
 cout<<str1<<endl;//A  
return 0;  
 \}  
  
  
6.string对象相加（非成员函数）  
operator+：  
 原型：  
template< class CharT, class Traits, class Alloc >  
basic\_string<CharT,Traits,Alloc>  
operator+( const basic\_string<CharT,Traits,Alloc>& lhs,  
const basic\_string<CharT,Traits,Alloc>& rhs );  
  
template< class CharT, class Traits, class Alloc >  
basic\_string<CharT,Traits,Alloc>  
operator+( const CharT\* lhs,  
const basic\_string<CharT,Traits,Alloc>& rhs );  
  
  
template< class CharT, class Traits, class Alloc >  
basic\_string<CharT,Traits,Alloc>  
operator+( CharT lhs,  
const basic\_string<CharT,Traits,Alloc>& rhs );  
  
template< class CharT, class Traits, class Alloc >  
basic\_string<CharT,Traits,Alloc>  
operator+( const basic\_string<CharT,Traits,Alloc>& lhs,  
const CharT\* rhs );  
  
template<class CharT, class Traits, class Alloc>  
basic\_string<CharT,Traits,Alloc>  
operator+( const basic\_string<CharT,Traits,Alloc>& lhs,  
CharT rhs );  
eg:  
int main()  
\{  
string str1("hello,");  
string str2("nihao,");  
cout<<str1+str2<<endl;//hello,nihao,  
 cout<<"Hi,"+str2<<endl; //Hi,nihao,  
 cout<<'A'+str2<<endl; //Anihao,  
 cout<<str1+"nihao,"<<endl; //hello,nihao,  
 cout<<str1+'B'<<endl; //hello,B  
 return 0;  
 \}  
  
  
7.下标操作符：  
访问指定的字符  
operator\[\]  
原型：  
reference operator\[\]( size\_type pos );  
const\_reference operator\[\]( size\_type pos ) const;  
eg:  
int main ()  
\{  
std::string str ("hello");  
for (int i=0; i<str.size(); ++i)  
\{  
std::cout << str\[i\]; //hello  
 \}  
 return 0;  
 \}**

**8.字符的处理（\#include<cctype>)**

**\*cctype常用函数：**

**![20130705164239734][]**

**int main ()  
\{  
string str ("hello,how are you!");  
int count=0;  
for (int i=0; i<str.size(); ++i)  
\{  
 if(ispunct(str\[i\]))  
 \{  
\++count;  
 \}  
str\[i\]=toupper(str\[i\]);  
\}  
cout<<str<<endl;//HELLO,HOW ARE YOU!  
 cout<<"punctuation count: "<<count;//punctuation count:2  
 return 0;  
\}**

[20130705164239734]: /images/20220113/6cdd0ee5dcd6499a87d3ed866fa1299a.png