字符串

 一.字符串常用函数

#include <iostream>
#include <fstream>
#include <string>
#include <string.h>
using namespace std;

int main()
{
    string s(4,'x');
    cout << s << endl;//xxxx

    s += "xx";

    string buffer = "E:\1.txt";
    ifstream infile;
    infile.open(buffer.c_str());//返回

    //erase
    string s1 = "This is a test string";
    s1.erase(10, 5);
    cout << s1 << endl;//This is a string

    //Insert
    string s2 = "test ";
    s1.insert(10, s2);
    cout << s1 << endl;//This is a test string

    //replace
    s1 = "This is a string";
    s1.replace(10, 6, s2);
    cout << s1 << endl;//This is a test

    //swap
    s1.swap(s2);
    cout << s1 << endl; // test

    s2[2] = 'a'; s2[3] = 't';
    cout << s2 << endl;//That is a test

    //substr
    s1 = s2.substr(10, 4);
    cout << s1 << endl;//test

    //find(子串,初始查找位置）
    cout << s2.find("is", 0) << endl;//5
    cout << s2.find("at", 0) << endl;//2

    //rfind(子串,初始查找位置)从后往前找
    cout << s2.rfind("a", 13) << endl;//8
    cout << s2.rfind("t", 13) << endl;//13

    //find_first_of,find_first_not_of
    //find_last_of,find_last_not_of
    s1 = "abcdef";
    cout << s1.find_first_of("xeyz") << endl;//4
    cout << s1.find_first_not_of("xyba") << endl;//2
    cout << s1.find_last_of("xeyz") << endl;//4
    cout << s1.find_last_not_of("xyba") << endl;//5

    //string.h strlen, strcmp, strcpy, atoi, strtok, strcat
    cout << strlen(s1.c_str()) << endl;//6 abcdef

    //c_str()是const char*
    char s3[500];
    strcpy(s3, s1.c_str());
    cout << s3 << endl;//abcdef

    char s4[500];
    strcpy(s4, s2.c_str());
    cout << strcmp(s3, s3) << endl;//0
    cout << strcmp(s3, s4) << endl;//1

    cout << strcat(s3, s4) << endl;//abcdefThat is a test

    strcpy(s3, "123");
    cout << atoi(s3) << endl;//123

    s1 = "123 456,789,你好";
    strcpy(s3, s1.c_str());
    char *p = strtok(s3, " ");
    while((p = strtok(NULL, ",")))
    {
        cout << p << endl;
        /*
        123
        456
        789
        你好
        */
    }
    return 0;
}

 二.getline

用来读入一整行到string类型变量中去，若getline没有读入字符，它将返回false，可用于判断是否结束以终止程序。

cin在getline之前使用，getline无法工作，cin的回车getline会读入，需要cin.ignore()

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

int main(int argc, char *argv[])
{

    string str;
    cin >> str1; //Ed wood
    cout << str1; //Ed, 自动忽略空格和之后内容

    return 0;
}

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

int main(int argc, char *argv[])
{

    string str;
    getline(cin, str); //Ed wood
    cout << str; //Ed wood

    return 0;
}

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

int main(int argc, char *argv[])
{

    ifstream infile;
    ofstream outfile;

    string buffer;

    infile.open("E:\3.txt");
    outfile.open("E:\2.txt", ios::app);

    while(getline(infile, buffer))
    {
        outfile << buffer << endl;
        /*
        Num = 1
        Num = 2
        Num = 3
        Num = 4
        Num = 5
        1
        2
        3
        4
        5

        */
    }

    infile.close();
    outfile.close();

    return 0;
}

三.字符串++

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

int main(int argc, char *argv[])
{
    string s1 = "1", s2 = "2";
    char s3[] = "3";//char[2]

    //左边必须string，+=同上
    s1 = s3;//ok
    s1 = s3;//ok
    s1 = 'l';//ok
    s3 = s1;//error

    string s4 = "";

    s1 = s2 + s3;//ok
    s1 = s2 + s4;//ok
    s1 = 'w' + s3;//ok
    s1 = "123" + "456";//error

    return 0;
}

四.补充

#include <iostream>
#include <fstream>
#include <string>
#include <string.h>
using namespace std;

int main()
{
    //assign
    string s1 = "cat";
    string s2;
    s2.assign(s1);
    cout << s2 << endl;//cat
    s2.assign(s1, 0, 2);
    cout << s2 << endl;//ca

    //append
    s1.append(s2);
    cout << s1 << endl;//catca
    s2.append(s1, 3, s1.size());//3至结束
    cout << s2 << endl;//caca

    //length,size
    cout << s1.length() << endl;//5
    cout << s1.size() << endl;//5

    //strstr
    //cout << strstr(s1.c_str(), s2.c_str()) << endl;//返回NULL
    s1.append(s2);
    cout << strstr(s1.c_str(), s2.c_str()) << endl;//返回s2在s1中首次出现的地址，cacaca

    //at
    string s3("hello");
    cout << s3[0] << " " << s3.at(0) << endl;//h h
    //cout << s3.at(7) << endl;//at会做范围检查，超出范围会抛出outofrange异常，下标运算符不会


    return 0;
}