std::string 简单入门

1. string的定义原型
   
   
   

typedef basic_string<char, char_traits<char>, allocator<char> >    string; 
typedef basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> >
    wstring;

// 第二三个参数有默认值

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2. string部分构造方式
   

// string 部分构造方式#include <iostream>
#include <string>
using namespace std;

int main(void)
{
    string s1;
    string s2("ABCDEFG");
    cout << s1 << endl;
    cout << s2 << endl;

    // 使用最初的形式定义
    basic_string<char> s3("xxxx");
    cout << s3 << endl;

    /*
        basic_string(
            const value_type *_Ptr, 
            size_type _Count
        );
    */
    string s4("DEFG", 2);
    cout << s4 << endl; // DE
    /*
        basic_string(
            const basic_string& _Right, 
            size_type _Roff,
            size_type _Count = npos
        );
    */
    string s5(s2, 2, 2);
    cout << s5 << endl; //CD

    /*
    basic_string(
       const_iterator _First,
       const_iterator _Last
    );
    */
    string::const_iterator first = s2.begin() + 1;
    string::const_iterator end = s2.begin() + 3; // [first, end)
    string s6(first, end);
    cout << s6 << endl; // BC

    return 0;


}

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2. string常用成员函数
   
   
   

// string 部分成员函数部分形式操作#include <iostream>
#include <string>
using namespace std;


int main(void)
{
    string s1("ABCDEC");
    cout << s1.size() << endl;
    cout << s1.length() << endl;

    cout << s1.empty() << endl;
    // 一样第二个参数是count,不是截至位置
    string s2 = s1.substr(1, /*4*/string::npos); // string::npos == 4294967295
    cout << s2 << endl;

    //find
    /*
        size_type find(
            value_type _Ch, 
            size_type _Off = 0
        ) const;
    */
    // 查找某个字符在string中第一次出现的位置（下标）,没找到返回 4294967295 最大值
    cout << s1.find('C') << endl; // 2
    //size_type -> size_t ->unsigned int
    /*
        size_type find(
            const value_type* _Ptr,
            size_type _Off = 0
        ) const;
    */
    // 在string中查找字符串，找到返回第一次出现位置的下标，没找到返回 string::npos， 4294967295 最大值
    cout << s1.find("CD") << endl; // 2
    /*
    size_type find(
        const basic_string<CharType, Traits, Allocator>& _Str,
        size_type _Off = 0
        ) const;
    */
    // 在string中查找string
    cout << s1.find(s2) << endl;

    //rfind,反向查找，返回第一次查找到的下标
    cout << s1.rfind('C') << endl; // 5

    //replace
    /*
        basic_string<CharType, Traits, Allocator>& replace(
           size_type _Pos1, 
           size_type _Num1,
           const value_type* _Ptr
        );
    */
    // 第三个参数也能是string，这里不写了，只介绍这一个好了
    string s3 = s1;
    s3.replace(1, 2, "RRR");
    cout << s3 << endl; // ARRRDEC

    // compare 
    cout << s3.compare(s1) << endl; // 1, s3 > s1

    // insert
    /*
        basic_string<CharType, Traits, Allocator>& insert(
           size_type _P0, 
           const value_type* _Ptr
        );
    */
    s3.insert(2, "aaaaaaaaaaa");
    cout << s3 << endl; // ARaaaaaaaaaaaRRDEC

    // append
    /*
        basic_string<CharType, Traits, Allocator>& append(
            const value_type* _Ptr
        );
    */
    s3.append("OOOOOOOOOOOOOOOOO");
    cout << s3 << endl; // ARaaaaaaaaaaaRRDECOOOOOOOOOOOOOOOOO

    // swap
    /*
        void swap(
            basic_string<CharType, Traits, Allocator>& _Str
        );
    */
    s3.swap(s2);
    cout << s3 << endl;
    cout << s2 << endl;

    return 0;
}

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2. string综合应用
   　　在字符集中查找存在的首尾字符，并截取。
   
   

#include <iostream>#include <string>
using namespace std;

int main()
{
    string strinfo = " //*---------Hello World!--------------*//";
    string strset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    /*
        size_type find_first_of(
            const basic_string<CharType, Traits, Allocator>& _Str,
            size_type _Off = 0
        ) const;
    */
    string::size_type first = strinfo.find_first_of(strset);
    if (first == string::npos)
        cout << "not found." << endl;
    string::size_type end = strinfo.find_last_of(strset);
    if (end == string::npos)
        cout << "not found." << endl;
    //cout << "string::npos" << string::npos << endl; // string::npos == 4294967295
    cout << strinfo.substr(first, end - first + 1) << endl;

    return 0;
}

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2. string简单去除字符串左右空格
   
   
   

// string 简单实现去除字符串左右空格#include <iostream>
#include <string>
using namespace std;

class StringUtils {
public:
    static void LTrim(string &s)
    {
        string drop = " \t";
        s.erase(0, s.find_first_not_of(drop));
    }

    static void RTrim(string &s)
    {
        string drop = " \t";
        s.erase(s.find_last_not_of(drop)+1);
    }

    static void Trim(string &s)
    {
        LTrim(s);
        RTrim(s);
    }
};

int main(void)
{
    string s1 = "               ABCD                ";
    StringUtils::Trim(s1);
    cout << s1 << endl; // "ABCD"
    cout << s1.size() << endl; // 4

    return 0;
}

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