String容器

  1 #include<iostream>
  2 #include<string>
  3 
  4 using namespace std;
  5 
  6 void test01() {
  7     string str1;  //string类默认构造
  8     string str2(str1);  //string类的拷贝构造
  9     string str3 = str1; //调用的是拷贝构造函数
 10 
 11     string str4 = "abcd";
 12     string str5("abcd");
 13     string str6(10,'a');  //用10个a初始化str6
 14     cout << str4 << endl;
 15     cout << str5 << endl;
 16     cout << str6 << endl;
 17 
 18     str1.assign("abcde", 3); //将给定字符串的前3个取出赋值给str1
 19     cout << str1 << endl;
 20 
 21     string str7;
 22     str7.assign("abcdefg", 2, 3); //从第2个位置开始拿三个给str7赋值
 23     cout << str7 << endl;
 24 }
 25 
 26 void test02() {   //取字符操作
 27     string s = "hello world";
 28 
 29     for (int i=0;i<s.size();i++)
 30     {
 31         //cout << s[i] << endl;
 32         cout << s.at(i) << endl;
 33     }
 34     try   //这里是为了探讨[]和at的区别，前者直接死掉，后者系统指明位置无效
 35     {
 36         //cout << s[50] << endl;
 37         cout << s.at(50) << endl;
 38     }
 39     catch (out_of_range &e)
 40     {
 41         cout << e.what() << endl;
 42     }
 43 }
 44 
 45 void test03() {  //拼接，查找，替换
 46     string s1 = "我";
 47     string s2 = "爱中国";
 48     s1 += s2;  //运算符重载
 49     cout << s1 << endl; 
 50     s1.append("山西");  //类内函数在当前字符串后加字符串
 51     cout << s1 << endl;
 52 
 53     string s3 = "abcdefg";
 54     int pos1 = s3.find("def");
 55     int pos2 = s3.rfind("def");  //两种方式均可以，只是查找方向不同而已
 56     cout << "pos1=" << pos1 << endl;
 57     cout << "pos2=" << pos2 << endl;
 58 
 59     string s4 = "hello";
 60     s4.replace(1, 2, "哪吒大战悟空");  //注意是段替换
 61     cout << s4 << endl;
 62 }
 63 
 64 void test04() {   //字符串比较
 65     string s1 = "abc";
 66     string s2 = "abcd";
 67     if (s1.compare(s2)==0)  
 68     {
 69         cout << "s1和s2相等" << endl;
 70     }
 71     else if (s1.compare(s2)==1)
 72     {
 73         cout << "s1大于s2" << endl;
 74     }
 75     else {
 76         cout << "s1小于s2" << endl;
 77     }
 78 }
 79 
 80 void test05() {    //获取字符串的字串
 81     string s1 = "abcdefg";
 82     string s2 = s1.substr(2, 4);
 83     cout << s2 << endl;
 84 
 85     //举例从邮件中获取一个用户名
 86     string email = "liming@qq.com";
 87     int pos = email.find("@");
 88     string username = email.substr(0,pos);
 89     cout << username << endl;
 90 }
 91 
 92 void test06() {    //字符串的插入、删除
 93     string s1 = "hello";
 94     s1.insert(2,"  abc  ");
 95     cout << s1 << endl;
 96 
 97     s1.erase(2,7);
 98     cout << s1<<endl;
 99 }
100 
101 //char *类型的字符串和string类型的字符串的转换
102 void func1(string s) {
103     cout << s << endl;
104 }
105 void func2(const char *s) {
106     cout << s << endl;
107 }
108 void test07() {
109     string s = "abc";
110     const char *p = s.c_str();  //注意const不能少
111     func2(p);
112 
113     const char *pp = "abcdefg";  //注意const不能少
114     string ss(pp);
115     func1(ss);
116 }
117 
118 void test08()
119 {
120     string s = "abcde";
121     char& a = s[2];
122     char& b = s[3];
123 
124     a = '1';
125     b = '2';
126 
127     cout << s << endl;
128     cout << (int*)s.c_str() << endl; //注意这里打印的是地址
129 
130     s = "ppppppppppppppppp";
131 
132     a = '1';  //此时无法修改，原因是经过了内存的重新分配
133     b = '2';  //此时a，b还指向原来的地址，所以出错
134 
135     cout << s << endl;
136     cout << (int*)s.c_str() << endl;
137 
138 }
139 
140 void test09() {   //变大写和变小写
141     string s = "abCdEfg";
142 
143     for (int i = 0; i < s.size(); i++)
144     {
145         //s[i] = toupper(s[i]);
146 
147         //全变小写
148         s[i] = tolower(s[i]);
149     }
150     cout << s << endl;
151 }
152 
153 int main() {
154     //test01();
155     //test02();
156     //test03();
157     //test04();
158     //test05();
159     //test06();
160     //test07();
161     //test08();
162     test09();
163     system("pause");
164     return 0;
165 }