STL：字符串用法详解

字符串是程序设计中最复杂的变成内容之一。STL string类提供了强大的功能，使得许多繁琐的编程内容用简单的语句就可完成。string字符串类减少了C语言编程中三种最常见且最具破坏性的错误：超越数组边界；通过违背初始化或被赋以错误值的指针来访问数组元素；以及在释放了某一数组原先所分配的存储单元后仍保留了“悬挂”指针。

string类的函数主要有：

Member functions

(constructor): Construct string object (public member function )

(destructor): String destructor (public member function )

operator=: String assignment (public member function )

Iterators:

begin: Return iterator to beginning (public member function )

end: Return iterator to end (public member function )

rbegin: Return reverse iterator to reverse beginning (public member function )

rend: Return reverse iterator to reverse end (public member function )

cbegin: Return const_iterator to beginning (public member function )

cend: Return const_iterator to end (public member function )

crbegin: Return const_reverse_iterator to reverse beginning (public member function )

crend: Return const_reverse_iterator to reverse end (public member function )

Capacity:

size: Return length of string (public member function )

length: Return length of string (public member function )

max_size: Return maximum size of string (public member function )

resize: Resize string (public member function )

capacity: Return size of allocated storage (public member function )

reserve: Request a change in capacity (public member function )

clear: Clear string (public member function )

empty: Test if string is empty (public member function )

shrink_to_fit: Shrink to fit (public member function )

Element access:

operator[]: Get character of string (public member function )

at: Get character in string (public member function )

back: Access last character (public member function )

front: Access first character (public member function )

Modifiers:

operator+=: Append to string (public member function )

append: Append to string (public member function )

push_back: Append character to string (public member function )

assign: Assign content to string (public member function )

insert: Insert into string (public member function )

erase: Erase characters from string (public member function )

replace: Replace portion of string (public member function )

swap: Swap string values (public member function )

pop_back: Delete last character (public member function )

String operations:

c_str: Get C string equivalent (public member function )

data: Get string data (public member function )

get_allocator: Get allocator (public member function )

copy: Copy sequence of characters from string (public member function )

find: Find content in string (public member function )

rfind: Find last occurrence of content in string (public member function )

find_first_of: Find character in string (public member function )

find_last_of: Find character in string from the end (public member function )

find_first_not_of: Find absence of character in string (public member function )

find_last_not_of: Find non-matching character in string from the end (public member function )

substr: Generate substring (public member function )

compare: Compare strings (public member function )

Member constants

npos: Maximum value for size_t (public static member constant )

Non-member functions overloads

operator+: Concatenate strings (function )

relational operators: Relational operators for string (function )

swap: Exchanges the values of two strings (function )

operator>>: Extract string from stream (function )

operator<<: Insert string into stream (function )

getline: Get line from stream into string (function )

1.string对象的定义和初始化

初始化string对象的几种方式有：

string s1;//默认构造函数，s1为空串
string s2(s1);//将s2初始化为s1的一个副本
string s3("value");//将s3初始化为value
string s4(n,'c');//将s4初始化为字符'c'的n个副本
string s5(s4,0,3)//从s4中下标为0的字符开始，连续取3个字符构成s5
string s6 = s5 + "value";//value 接在s5后面，注意+操作符的左右操作数至少有一个是string类型的
迭代器创建，由于可将string看作字符的容器对象，因此可以给string类的构造函数传递两个迭代器，将它们之间的数据复制到心的string对象中。

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#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
string s1("How are you");
string s2(s1.begin(),s1.end());
string s3(s1.begin()+4,s1.begin()+7);
cout<<s1<<endl;
cout<<s2<<endl;
cout<<s3<<endl;
return 0;
}

2.string 对象的读写

string对象的读写可以通过两个方式：

通过cin从标准输入中读取，cin忽略开题所有的空白字符，读取字符直至再次遇到空白字符，读取终止。
用getline读取整行文本,getline函数接受两个参数：一个输入流对象和一个string对象。getline函数从输入流的下一行读取，并保存读取的内容到string中，但不包括换行符。和输入操作符不一样的是，getline并不忽略开头的换行符。即便它是输入的第一个字符，getline也将停止读入并返回。如果第一个字符就是换行符，则string参数将被置为空string。

3.string对象的插入操作

字符串一般通过包括首字符前、尾字符后、任意位置插入等几种情况。

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#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
string s1("do");
cout<<"Initial size is:"<<s1.size()<<endl;
s1.insert(0,"How ");
s1.append(" you");
s1 = s1 + " do ?";
cout<<"Final size is:"<<s1.size()<<endl;
cout<<s1<<endl;
return 0;
}

程序运行结果如下：

通过该函数可以得出：

insert函数，第一个参数表明插入源串的位置，第二个参数表面要插入的字符串，因此利用该函数可以实现串首、串尾及任意位置处的字符串插入功能。
append函数，仅有一个输入参数，在源字符串尾部追加该字符串。
利用+实现字符串的连接，从而创建新的字符串。

4.替换操作

常用的是replace函数，有三个输入参数：第一个用于指示从字符串的什么位置开始改写，第二个用于指示从源字符串中删除多少个字符，第三个是替换字符串的值。

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#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
string s1("I love you forever !");
cout<<"替换前："<<s1<<endl;
s1.replace(7,3,"dachun");
cout<<"替换后"<<s1<<endl;
return 0;
}

程序运行结果如下：

5.查询操作

查询常用的函数有：

string::npos:这是string类中的一个成员变量，一般应用在判断系统查询函数的返回值上，若等于该值，表明没有符合查询条件的结果值。
find函数：在一个字符串中查找指定的单个字符或字符组。如果找到，就返回首次匹配的开始位置；如果没有找到匹配的内容，则返回string：：npos。一般有两个输入参数，一个是待查询的字符串，一个是查询的起始位置，默认起始位置为0.
find_first_of函数：在一个字符串中进行查找，返回值是第一个与指定字符串中任何字符匹配的字符位置；如果没有找到匹配的内容，则返回string：：npos。一般有两个输入参数，一个是待查询的字符串，一个是查询的起始位置，默认起始位置为0.
find_last_of函数：在一个字符串中进行查找，返回值是最后一个与指定字符串中任何字符匹配的字符位置；如果没有找到匹配的内容，则返回string：：npos。一般有两个输入参数，一个是待查询的字符串，一个是查询的起始位置，默认起始位置为0.
find_first_not_of函数：在一个字符串中进行查找，返回值是第一个与指定字符串中任何字符都不匹配的字符位置；如果没有找到匹配的内容，则返回string：：npos。一般有两个输入参数，一个是待查询的字符串，一个是查询的起始位置，默认起始位置为0.
find_last_not_of函数：在一个字符串中进行查找，返回下标值最大的与指定字符串中任何字符都不匹配的字符位置；如果没有找到匹配的内容，则返回string：：npos。一般有两个输入参数，一个是待查询的字符串，一个是查询的起始位置，默认起始位置为0.
rfind函数：对一个串从尾至头查找指定的单个字符或字符组，如果找到，就返回首次匹配的开始位置；如果没有找到匹配的内容，则返回string：：npos。一般有两个输入参数，一个是待查询的字符串，一个是查询的起始位置，默认起始位置为0.

[cpp] view plain copy

#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
string s1("what's your name? my name is TOM. How do you do? Fine,thanks.");
int n = s1.find("your");
cout<<"the first your pos:"<<n<<endl;
n = s1.find("you",15);
cout<<"the first you pos begin from 15:"<<n<<endl;
n = s1.find_first_of("abcde");
cout<<"find pos when character within abcde:"<<n<<endl;
n = s1.find_first_of("abcde",3);
cout<<"find pos when character within abcde from third character:"<<n<<endl;
return 0;
}

程序运行结果如下：

6.删除字符操作

主要用erase函数，有两个迭代器输入参数，之间表示的字符将被删除掉。

[cpp] view plain copy

#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
int _tmain(int argc, _TCHAR* argv[])
{
string s1("what's your name? my name is TOM. How do you do? Fine,thanks.");
s1.erase(s1.begin(),s1.begin()+17);
cout<<"after erase to s1 is:"<<s1<<endl;
string s2 = "i love you forever!";
s2.erase(s2.begin(),s2.end());
cout<<"after erase to s2 is"<<s2<<endl;
return 0;
}

程序运行结果如下：

7.比较操作

主要是一句ASCII值来比较大小。若字符串s1“大于”s2，表明两者相比较时遇到了第一对不同的字符，字符串s1中第一个不同的字符比字符串s2中同样位置的字符在ASCII表中位置更靠后。

C++ STL提供了多钟字符串比较方法，他们各具特色。其中最简单的就是使用非成员的重载运算符函数operator==、operator!=、operator>、operator<、operator>=和operator<=。