string基本字符系列容器

#include<string>
#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<sstream>
using namespace std;

///c++方法，将数值转换为string
string convertTOString(double x){
    ostringstream o;
    if(o << x)
        return o.str();
    return "concersion error";///if error
}
///c++方法，将string转换为数值
double convertFromString(const string &s){
    istringstream i(s);
    double x;
    if(i >> x)
        return x;
    return 0.0;///if error
}

int main(){
    ///创建字符对象s
    string s;
    cout << s.length() <<endl;

    ///对s赋值
    s = "Hello world";
    cout << s << endl;

    ///在string对象尾部添加字符
    s = s + 'a';
    s = s + 'b';
    s = s + 'c';
    cout << s << endl;

    ///在string对象尾部添加字符串
    ///1.采用"+"操作符
    s += "abc";
    ///2.采用append()方法
    s.append("123");
    cout << s << endl;

    ///给string对象插入字符
    s.clear();
    s = "111111";
    ///定义迭代器
    string::iterator it;
    it = s.begin();
    s.insert(it+1,'p');
    cout << s << endl;

    ///访问string对象的元素
    ///通过下标访问
    s.clear();
    s = "123456";
    cout << s[3] << endl;

    ///删除string对象的元素
    ///定义迭代器变量指向首元素
    it = s.begin();
    s.erase(it+3);
    cout << s << endl;
    s.erase(it,it+4);
    cout << s << endl;

    ///返回string对象的长度
    printf("长度：\n");
    cout << s.size() << endl;
    printf("是否为空:\n");
    cout << s.empty() << endl;

    ///替换string对象的字符
    s = "123456789";
    cout << s << endl;
    s.replace(3,3,"good");
    cout << s << endl;

    ///搜索string对象的元素或字串
    s = "cat dog cat";
    ///查找第一个子符'c'，返回下标值
    cout << s.find('c') << endl;
    ///查找第一个子串"c"，返回下标值
    cout << s.find("c") << endl;
    ///查找第一个子串"cat"，返回下标值
    cout << s.find("cat") << endl;
    ///查找第一个子串"dog",返回下标值
    cout << s.find("dog") << endl;
    ///查找第一个子串"dogc"，不存在返回4294967295
    cout << s.find("dogc") << endl;

    ///string对象的比较
    ///s比cat大，返回1；
    cout << s.compare("cat") << endl;
    ///s和"cat dog cat"相等返回0
    cout << s.compare("cat dog cat") << endl;
    ///s比"dog"小返回-1；
    cout << s.compare("dog") << endl;

    ///用reverse反向排序string对象
    s = "123456789";
    reverse(s.begin(),s.end());
    cout << s << endl;

    ///string对象作为vector元素
    vector<string> v;
    v.push_back("JACK");
    v.push_back("MIKE");
    v.push_back("TOM");
    cout << v[0] << endl;
    cout << v[1] << endl;
    cout << v[2] << endl;
    cout << v[0][0] << endl;
    cout << v[1][0] << endl;
    cout << v[2].length() << endl;

    ///string对象与字符数组相互操作
    s.clear();
    char ss[100] = "abc123";
    ///字符数组赋值字符串对象
    s = ss;
    ///用printf输出字符串对象用c_str()方法
    printf(s.c_str());
    printf("\n");

    ///string对象与sscanf函数
    string s1,s2,s3;
    char sa[100],sb[100],sc[100];
    ///将字符串分离成字串，分隔符为空格
    sscanf("abc 123 pc","%s %s %s",sa,sb,sc);
    s1 = sa;
    s2 = sb;
    s3 = sc;
    cout << s1 << " " << s2 << " " << s3 << endl;
    ///将字符串分离成数字，分隔符为空格
    ///当用到数字时，和scanf一样，它要传指针地址
    int a,b,c;
    sscanf("1 2 3","%d %d %d",&a,&b,&c);
    cout << a << " " << b << " " << c << endl;
    ///将字符串分离成数字，分隔符为“，”和“$”；
    int x,y,z;
    sscanf("4,5$6","%d,%d$%d",&x,&y,&z);
    cout << x << " " << y << " " << z << endl;

    ///string对象与数值相互转换
    ///将数值转换为string的c方法
    char g[10];
    string h;
    sprintf(g,"%d",1975);
    h = g;
    cout << h << endl;
    ///将数值转换为string的第二种方法：c++版
    string cc = convertTOString(1976);
    cout << cc << endl;
    ///string转换为数值的方法：c++版
    string dd = "2006";
    int p = convertFromString(dd)+2;
    cout << p <<endl;

    return 0;
}