Standard Template Library Basis [6] string

说明：代码均省略其输出验证步骤

[1] 赋值语句

#include<iostream> 
#include<map> 
#include<string> 
#include<utility> 
#include<vector>
#include<string>
using namespace std;
int main()
{
    //string与c语言的\0表示结尾不一样
    string a1(10,'a');
    cout<<a1<<endl;
    string a2(10,'\0');
    cout<<a2.size()<<endl;//size()和length()一样长
    
    string a3="222";
    //不能string a3='2';
    
    string a6("nihao",20);//表示长度是20，后面接上\0
    
    string a7({'x','y','z'});
    cout<<a7<<endl;
    
    return 0;
}

[2]简单介绍，string与printf的协作，与字符数组的区别

#include<iostream> 
#include<map> 
#include<string> 
#include<utility> 
#include<vector>
#include<string>
using namespace std;
int main()
{
    //string与printf的协作，.c_str(）自动帮忙添上\0
    string a1="nihao";
    printf("Guten Morgen! %s\n",a1.c_str());
    
    char v[100];
    a1.copy(v,100);
    
    char v1[100];
    a1.copy(v1,100,2);//从下标为2的字符开始拷贝
    
    cout<<v<<endl;//会出现乱码
    
    //不会有乱码了
    v[a1.size()]='\0';
    cout<<v<<endl;
    
    return 0;
}

[3]赋值语句

#include<iostream> 
#include<map> 
#include<string> 
#include<utility> 
#include<vector>
#include<string>
#include<cstring>
using namespace std;
int main()
{
    string a1;
    string a2("nihaodajiahao");
    
    string a3(a2,2);//从a2的第二个字符向后面取

    string a4(a2,2,4);
    
    string a5(a4);
    
    string a6("everybodydancewiththedeath",2);
    //去前两个字符：ev,是c语言的字符串，要有所区分
    
    string a7(20,'x');//20个x
    
    char v[]="nihao";
    int n=strlen(v);
    string a9(v,v+n);
   
    string a10(a2.begin(),a2.begin()+2);
    
    string a11{'x','x','c'};
    
    //a11.empty()也一样用
    
    //string的大小按照字典序大小比较
    
    return 0;
}

[4]对字符串中字符的访问

#include<iostream> 
#include<map> 
#include<string> 
#include<utility> 
#include<vector>
#include<string>
#include<cstring>
using namespace std;
int main()
{
    //字符串的大小比较
    string a1="hello";
    string a2="Nihao";
    
    //比较满足：
    cout<<(a1<"zzz")<<endl;
    cout<<("zzz"<a1)<<endl;
    cout<<(a1<a2)<<endl;
    //不能这么比：
    cout<<("hfjha"<"jfakj")<<endl;
    
    //另一种比较方法：
    cout<<a1.compare(a2)<<endl;//大于0则a1>a2
    cout<<a1.compare(1,3,a2)<<endl;//从1位向后取三个字符
    cout<<a1.compare(1,3,a2,1,2)<<endl;
    cout<<a1.compare("hello")<<endl;//也可以直接用原生字符串
    return 0;
}

[5]字符串的访问

#include<iostream> 
#include<map> 
#include<string> 
#include<utility> 
#include<vector>
#include<string>
#include<cstring>
using namespace std;
int main()
{
    //字符串的访问
    string a1="nihaodajiahao";
    cout<<a1[4]<<endl;//或者cout<<a1.at(3)<<endl;
    
    //全部转换成大写
    for(int i=0;i<a1.size();i++)
    {
        a1[i]=toupper(a1[i]);
    }
    
    //访问第一个和最后一个
    cout<<a1.front()<<endl;
    cout<<a1.back()<<endl;
    
    //使用引用或者指针
    char &p=a1[0];//引用
    p='X';
   
    char &q=a1.back();//引用
    q='L';
    
    //还有a1.copy()操作
    return 0;
}

[6].assign() .swap()

#include<iostream> 
#include<map> 
#include<string> 
#include<utility> 
#include<vector>
#include<string>
#include<cstring>
using namespace std;
int main()
{
    //字符串的修改
    string a1="nihaodajiahao";
    a1="nihao";
    
    //或者：
    a1.assign("miaomiaomiao");
    
    string a2;
    a2.assign(a1,3,4);//从3开始向后取4个
    cout<<a2<<endl;
    
    a2.assign("aaa",100);
    cout<<a2.size()<<endl;
    
    //交换
    a1.swap(a2);//成员函数
    swap(a1,a2);//算法
    return 0;
}

[7].insert()

#include<iostream>
#include<string>
using namespace std;
int main()
{
    //插入 .insert()
    string a1="abcdefg";
    string b1="xxxcc";
    a1.insert(2,b1);
    
    a1="abcdefg";
    a1.insert(3,b1,1,3);
    
    a1="abcdefg";
    a1.insert(3,"xxx");
    
    a1="abcdefg";
    a1.insert(3,"xxx",2);
   
    //可以用迭代子a1.insert(p1,'x');
    //可以用迭代子a1.insert(p1,p2,p3);p2、p3属于b
    //可以用迭代子a1.insert(p1,{'x','y'));p2、p3属于b
    
    
    return 0;
}

[8]清除 .erase(), .clear() .resize(), .pop_back()

#include<iostream>
#include<string>
using namespace std;
int main()
{
    string a1="12345678";
    a1.clear();//清空
    //等价a1.erase();
    
    a1="12345678";
    a1.erase(2,3);
    cout<<a1<<endl;
    
    //a1.erase(p1);
    //a1.erase(p2,p3);
    //a1.pop_back();C++11
    //a1.resize();
    
    return 0;
}

[9]替换

#include<iostream>
#include<string>
using namespace std;
int main()
{
    //替换
    string a1="12345678";
    string b1="XXXXXX";
    
    a1.replace(2,3,b1);//2-3位替换为b1
    
    a1="12345678";
    a1.replace(2,3,b1,2,1);
    
    //以上的数字均可以替换为迭代子
    
    a1="12345678";
    a1.replace(2,3,10,'x');//10个x
    return 0;
}

[10]查找

#include<iostream>
#include<string>
using namespace std;
int main()
{
    //查找 .find()
    string a1="123456786";
    int i1=a1.find('6');
    cout<<i1<<endl;
    
    int i2=a1.find('6',i1+1);//从i+1之后向后查找
    cout<<i2<<endl;
    
    //显示所有的h
    string s="hajfhnchdfjiefh";
    int i=0;
    while(i<s.size())
    {
        int t=s.find('h',i);
        cout<<t<<" ";
        i=t+1;
    }
    
    //逆向查找
    cout<<s.rfind('h');
    
    return 0;
}

[11]集合的查找.find_first_of() .find_last_of()

#include<iostream>
#include<string>
using namespace std;
int main()
{
    //find_first_of 在集合中查找
    string a1="abcdefghijklmn";//a1看成是字符串
    string b1="xzghn";//b1当成集合看
    int i1=a1.find_first_of(b1);
    cout<<a1[i1]<<endl;
    
    i1=a1.find_first_not_of(b1);
    cout<<i1<<endl;
    
    return 0;
}

[12]拼接

#include<iostream> 
#include<string> 
#include<cstring>
using namespace std;
int main() {
    string a1 = "abcdefghijklmn";
    
    string b1 = a1.substr(3);
    cout << b1 << endl;
    
    string b2 = a1.substr(3, 4);
    cout << b2 << endl;
    
    
    string a2 = "nihao";
    string a3 = "dajiahao";
    string b3 = a2 + a3;
    cout << b3 << endl;
    
    string b4 = 'X' + a2;
    cout << b4 << endl;
    
    string b5 = a2 + 'X';
    cout << b5 << endl;
  
    return 0;
}

[13]输入cin和getline

直接cin:[不能有空格]

#include<iostream> 
#include<string> 
#include<cstring>
using namespace std;
int main() {
    string a1;
    cin >> a1;
    cout << a1 << endl;
    //输入时不能有空格 system("pause");
    return 0;
}

getline：[可以有空格]

#include<iostream>
#include<string> 
#include<cstring>
using namespace std;
int main() {
    string a1;
    getline(cin, a1);
    cout << a1 << endl;//输入时不能有空格 system("pause");
    return 0;
}

[14]数字与字符串之间的转换

数字转字符串

#include<iostream> 
#include<string> 
#include<cstring>
using namespace std; //数字转字符串 直接用 to_string
int main()
{
    string a1 = to_string(118);//"118" cout << a1 << endl;
    a1 = to_string(123.4567);
    cout << a1 << endl;//"123.456700" a1.pop_back();
    
    a1.pop_back();
    cout << a1 << endl;
    system("pause");
    return 0;
}

字符串转数字（含进制的转化）

#include<iostream> 
#include<string> 
#include<cstring>
using namespace std;
int main() {
    //stoi s:string i:int
    int a1 = stoi("77");
    cout << a1<< endl;
    
    a1 = stoi(" 77");
    cout << a1 << endl;
    
    a1 = stoi("    77xcvb");
    cout << a1 << endl;
    
    std::size_t t;
    a1 = stoi("    77xcvb", &t);
    cout << t << endl;
    
    a1 = stoi("77xcvb", &t);//转化不动时候的下标
    cout << t << endl;
    
    a1 = stoi("1239", nullptr, 8);//8进制的123转化为十进制为83（没有9）
    cout << a1 << endl;
    
    a1 = stoi("1239", &t, 8);
    cout << t << endl;//显示地址3
    cout << a1 << endl;//83
    return 0;
}

#include<iostream> 
#include<string> 
#include<cstring> 
#include<limits>
using namespace std; //数字转字符串 直接用 to_string
int main()
{
    // stoi       string to int
    // stol       string to long
    // stoul      string to unsigned long
    // stoll      string to long long
    // stoull     string to unsigned long long
    // stof       string to float
    // stod       string to double
    // stold      string to long double
    std::size_t idx;
    cout << stoi("    42 is the truth",&idx)<<endl;
    cout << " idx of first unprocessed char: " << idx << endl;
    cout << stoi(" 42", nullptr, 16) << endl;
    cout << stol("789", &idx, 8) << endl;
    cout << " idx of first unprocessed char: " << idx << endl;
    long long ll = numeric_limits<long long>::max();
    string sss = to_string(ll);
    cout << ll << endl;
    return 0;
}