实战c++中的string系列--string的连接(+= or append or push_back)

string的连接也是经常用到的，string重载了一些运算符：
首先看一看重载+运算符，用于串联两个字符串对象：
源码：

template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator> operator+(      const basic_string<CharType, Traits, Allocator>& _Left,      const basic_string<CharType, Traits, Allocator>& _Right   );template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator> operator+(      const basic_string<CharType, Traits, Allocator>& _Left,      const CharType* _Right   );template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator> operator+(      const basic_string<CharType, Traits, Allocator>& _Left,      const CharType _Right   );template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator> operator+(      const CharType* _Left,      const basic_string<CharType, Traits, Allocator>& _Right   );template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator> operator+(      const CharType _Left,      const basic_string<CharType, Traits, Allocator>& _Right   );template<class CharType, class Traits, class Allocator>    basic_string<CharType, Traits, Allocator>&& operator+(        const basic_string<CharType, Traits, Allocator>& _Left,        const basic_string<CharType, Traits, Allocator>&& _Right);template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator>&& operator+(      const basic_string<CharType, Traits, Allocator>&& _Left,      const basic_string<CharType, Traits, Allocator>& _Right);template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator>&& operator+(      const basic_string<CharType, Traits, Allocator>&& _Left,      const basic_string<CharType, Traits, Allocator>&& _Right);template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator>&& operator+(      const basic_string<CharType, Traits, Allocator>&& _Left,      const CharType *_Right);template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator>&& operator+(      const basic_string<CharType, Traits, Allocator>&& _Left,      CharType _Right);template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator>&& operator+(      const CharType *_Left,      const basic_string<CharType, Traits, Allocator>&& _Right);template<class CharType, class Traits, class Allocator>   basic_string<CharType, Traits, Allocator>&& operator+(      CharType _Left,      const basic_string<CharType, Traits, Allocator>&& _Rig

所以使用时，注意事项：

#include<iostream>#include<string>int main(){    std::string my_str = "holiday";    std::string my_str_add = "error" + "error";//错误    std::string my_str_add2 = my_str + "right";    std::string my_str_add3 = my_str + "right" + "right";    std::string my_str_add4 = "right" + my_str;    std::string my_str_add5 = "error" + "error" + my_str;//错误    return 0;}

下面开始正题!
+=
*将字符追加到字符串*

basic_string<CharType, Traits, Allocator>& operator+=(   value_type _Ch);basic_string<CharType, Traits, Allocator>& operator+=(   const value_type* _Ptr);basic_string<CharType, Traits, Allocator>& operator+=(   const basic_string<CharType, Traits, Allocator>& _Right);

append
*添加字符为字符串的末尾*

basic_string<CharType, Traits, Allocator>& append(    const value_type* _Ptr);basic_string<CharType, Traits, Allocator>& append(    const value_type* _Ptr,    size_type _Count);basic_string<CharType, Traits, Allocator>& append(    const basic_string<CharType, Traits, Allocator>& _Str,    size_type _Off,    size_type _Count);basic_string<CharType, Traits, Allocator>& append(    const basic_string<CharType, Traits, Allocator>& _Str);basic_string<CharType, Traits, Allocator>& append(    size_type _Count,     value_type _Ch);template<class InputIterator>    basic_string<CharType, Traits, Allocator>& append(        InputIterator _First,         InputIterator _Last    );basic_string<CharType, Traits, Allocator>& append(    const_pointer _First,    const_pointer _Last);basic_string<CharType, Traits, Allocator>& append(    const_iterator _First,    const_iterator _Last);

有多个重载函数，因此多种使用方法：

   string str1a ( "Hello " );   const char *cstr1a = "Out There ";   str1a.append ( cstr1a );   string str1b ( "Hello " );   const char *cstr1b = "Out There ";   str1b.append ( cstr1b , 3 );   string str1c ( "Hello " ), str2c ( "Wide World " );      str1c.append ( str2c , 5 , 5 );   string str1d ( "Hello " ), str2d ( "Wide " ), str3d ( "World " );   str1d.append ( str2d );   str1d += str3d;   string str1e ( "Hello " );   str1e.append ( 4 , '!' );   string str1f ( "Hello " ), str2f ( "Wide World " );   str1f.append ( str2f.begin ( ) + 5 , str2f.end ( ) - 1 );

push_back
*将元素添加到该字符串的末尾*

void push_back(    value_type _Ch);

这里需要注意的是，以下代码是错误的：

my_str.push_back("123");//错误my_str.push_back('1');//ok