1、字符串插入

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <string>
#include <assert.h>
using namespace std;void test_string8()
{//insert 尽量少用string str("wo lai le");//（1）在空格的位置插入 20%for (size_t i = 0; i < str.size(); ++i){if (' ' == str[i]){str.insert(i, "20%");i += 4;}else{++i;}}cout << str << endl;//（2）用 20% 替换空格// 先插入20%，再删除空格for (size_t i = 0; i < str.size(); ++i){if (' ' == str[i]){str.insert(i, "20%");i += 3;}}cout << str << endl;for (size_t i = 0; i < str.size(); ++i){if (' ' == str[i]){str.erase(i, 1);}}cout << str << endl;//用空间换时间string newstr;for (size_t i = 0; i < str.size(); ++i){if (str[i] != ' '){newstr += str[i];}else{newstr += "20%";}}cout << newstr << endl;}

2、c_str

void test_string9()
{//要求:用C的形式读文件  // c_str() 是为了兼容一些c语言的用法而使用的。string filename("test.cpp");cout << filename << endl;cout << filename.c_str() << endl;filename += '\0';filename += "string.cpp";cout << filename << endl; //string对象 终止的标准是 _size;cout << filename.c_str() << endl; //而常量字符串的 终止标准是 '\0'cout << filename.size() << endl;string copy = filename;cout << copy << endl;/*FILE* fout = fopen(filename.c_str(),"r");assert(fout);char ch = fgetc(fout);while (ch != EOF){cout << ch;ch = fgetc(fout);}*/
}

3、分隔后缀

void DealUrl(const string& url)
{size_t pos1 = url.find("://");if (pos1 == string::npos){cout << "非法url" << endl;return;}string protocol = url.substr(0, pos1);cout << protocol << endl; //打印 协议size_t pos2 = url.find('/', pos1 + 3);if (pos2 == string::npos){cout << "非法url" << endl;return;}string domain = url.substr(pos1 + 3, pos2 - pos1 - 3);cout << domain << endl; //打印 域名string uri = url.substr(pos2 + 1);cout << uri << endl; //打印 统一资源标识符}void test_string10()
{//string filename("test.cpp.tar.zip");后缀//size_t pos = filename.rfind('.');//if (pos != string::npos)//{//	//string suff = filename.substr(pos,filename.size()-pos);//	string suff = filename.substr(pos);//	cout << suff << endl;//}string url1 = "https://cplusplus.com/reference/string/string/";string url2 = "ftp://ftp.cs.umd.edu/pub/skipLists/skiplists.pdf";DealUrl(url1);cout << endl;DealUrl(url2);}

4、字符串转化为数值，或数值转化为字符串

void test_string12()
{int ival;double dval;cin >> ival >> dval;string istr = to_string(ival); //整型转化为字符串string dstr = to_string(dval);cout << istr << endl;cout << dstr << endl;istr = "9999";dstr = "9999.99";ival = stoi(istr); // 字符串转化为整型dval = stod(dstr);cout << ival << endl;cout << dval << endl;
}int main()
{test_string12();return 0;
}