string类篇超超超详解，40余个成员函数详细解释(图文)！看完包会！！

本篇目标

constructor
operator=
Elements access
Iterators
Capacity
Modifiers
String operations
member contants
其他函数

一、constructor(对象的创建)

void StrTest1()
{string s1;//直接构造cout << s1 << endl;//string里内置了流插入、流提取的函数重载，可直接打印string s2("hello world");//字符常量构造，有隐式类型转换cout << s2 << endl;string s3("hello world", 5);//取常量字符串的前5个进行打印cout << s3 << endl;string s4(s3); //拷贝构造cout << s4 << endl;string s5(s2, 2);//从s2的第二个字符开始(0 1 2 也就是l位置，若不给长度，直接全部拷贝)cout << s5 << endl;string s6(s2, 2, 4);//从第二个字符开始拷贝，到第四个字符cout << s6 << endl;string s7(7, 'x');//用7个x对其进行初始化cout << s7 << endl;string s8(s2.begin(), s2.end());//调用begin和end成员函数，其返回迭代器(迭代器很像指针，但不只指针)cout << s8 << endl;
}

注意:end是返回指向容器最后一个位置下一个的迭代器，所以构造s8时，他的区间是左闭右开“[ )”的.

二、operator=(给对象赋值)

void StrTest2()
{string s2 = "hello world";//创建对象时直接初始化 ,相当于s2("hello world")cout << s2 << endl;string s3 = s2;//用类对象赋值初始化cout << s3 << endl;s2 = "5569";cout << s2 << endl;//string s4 = 'c';//错误，不能在创建对象时进行赋值字符string s4;cout << s4 << endl;s4 = 'a';cout << s4 << endl;}

三、Element access(元素访问)

3.1 oeprator[]

void StrTest3()
{string s3 = "hello world";//len = 11cout << s3 << endl;cout << s3.size() << endl;//可以看到，size=11,size是没有把'\0'算入的for (int i = 0; i < s3.size(); i++) {s3[i]++;cout << s3[i] ;}cout << endl;}

若是用const修饰对象

3.2 at

void StrTest4()
{string s3 = "hello world";const string s4 = "hello world";cout << s3 << endl;for (int i = 0; i < s3.size(); i++){s3.at(i)++;cout << s3.at(i)<<' ';}cout << endl;
}

3.3 back&front

void StrTest5()
{string s3 = "hello world";cout << s3.back() << endl;cout << s3.front() << endl;
}

四、Iterator(迭代器)

4.1 begin&end

在这里我们可以认为迭代器和指针很像(当然迭代器不知包括指针)，begin()返回指向首字符的指针

end返回指向最后一个字符的下一个位置的指针

下面我们将用3种不同的方式遍历串

void StrTest6()
{string s3 = "hello world";//方法一 operator[]for (int i = 0; i < s3.size(); i++) {cout << s3[i];}cout << endl;//方法二 atfor (int i = 0; i < s3.size(); i++) {cout << s3.at(i);}cout << endl;//方法三 迭代器string::iterator it1 = s3.begin();while (it1 != s3.end()){*it1 += 3;cout << *it1;it1++;}cout << endl;//方法四 遍历for循环for (auto& e : s3) {cout << e;}cout << endl;
}

4.2 rbegin&rend

这里的r有反向的意思，reversebegin和reverseend

下面使用这两个函数遍历字符串

void StrTest7()
{string s2("hello world");//从rbegin到rend//反向打印string::reverse_iterator it1 = s2.rbegin();while (it1 != s2.rend()){cout << *it1;it1++;}cout << endl;//正向打印//从rend到rbeginstring::reverse_iterator it2 = s2.rend()-1;//指向第一个字符while (it2 != s2.rbegin()){cout << *it2;it2--;}cout << *it2;cout << endl;
}

4.3 cbegin&cend& crbegin&crend

void StrTest8()
{string s3 = "hello world";string::const_iterator it1 = s3.cbegin();//这里的it1指向的内容就不能再改变了//其余的cend 、 crend 、 crbegin 除了是_const 以外，其他和前面两个函数一摸一样，不再赘述
}

五、Capacity(空间)

5.1 size&length&max_size

这两个都是返回字符串的长度，功能都基本相同

void StrTest9()
{string s1 = "hello world";//实际长度为12，包含'\0'cout << s1.length() << endl;cout << s1.size() << endl;
}

可以看出，vs编译器是不把'\0'算入size和length中的，编译器不同，得出的实际效果也就不同

可以看到，在64位机器下，编译器能给的最大空间很大很大，但实际上却给不了这么大的空间(即便身价500亿，亦不能随时掏出1个亿)

5.2 capacity

那么当我们扩大字符串长度/缩小，capacity会有变化吗

void StrTest9()
{string s1 = "hello world";//实际长度为12，包含'\0'cout << s1.length() << endl;cout << s1.size() << endl;cout << s1.capacity() << endl;s1 = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";cout << s1.capacity() << endl;s1 = "xxx";cout << s1.capacity() << endl;
}

可以很明显的看出，当我们扩大字符串的长度时，capacity会自动扩大，但当我们缩小字符串长度时，capacity却不会随之变小(capacity只扩大不缩小)

5.3 resize

void StrTest9()
{string s1 = "hello world";//实际长度为12，包含'\0'cout << s1.length() << endl;cout << s1.size() << endl;cout << s1.max_size() << endl;cout << s1.capacity() << endl;s1 = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";cout << s1.capacity() << endl;s1 = "xxx";cout << s1.capacity() << endl;//扩容至25，其余补充为cs1.resize(25, 'c');cout << s1 << endl;cout << s1.capacity() << endl;cout << s1.length() << endl;cout << s1.size() << endl;//扩容至50,这是会发现capacity也随之改变至70s1.resize(50,'X');cout << s1 << endl;cout << s1.capacity() << endl;cout << s1.length() << endl;cout << s1.size() << endl;//缩容至25s1.resize(25);//你会发现capacity不会变小，capacity只大不变小cout << s1 << endl;cout << s1.capacity() << endl;cout << s1.length() << endl;cout << s1.size() << endl;}

5.4 reserve

void StrTest10() {string s1 = "hello world";cout << s1 << endl;cout << s1.capacity() << endl;//15cout << s1.length() << endl;//11cout << s1.size() << endl;//11//现在我们来扩大capacity,那么capacity就一定是50吗？s1.reserve(50);cout << s1.capacity() << endl;//63 ，编译器其可能觉得50不好，自动优化到63cout << s1.length() << endl;//11cout << s1.size() << endl;//11//那现在我们来缩小capacity，你觉得有可能吗s1.reserve(25);cout << s1.capacity() << endl;//63 ，capacity还是63，根本不听你的cout << s1.length() << endl;//11cout << s1.size() << endl;//11//再次缩小s1.reserve(20);cout << s1.capacity() << endl;//63，还是没有缩小cout << s1.length() << endl;//11cout << s1.size() << endl;//11//再次缩小s1.reserve(13);//15 ，为什么这次就缩小了呢？//是因为其中内置了一个大小为15的数组，当空间小于15时(也就是串小于15)，会先存储到这个buffer区中cout << s1.capacity() << endl;//15,cout << s1.length() << endl;//11cout << s1.size() << endl;//11
}

注意：可以利用reserve提高插入数据的效率，避免增容带来的开销，一把开好，省得麻烦(如果知道要用多少)

5.5 clear&empty&shrink_to_fit

一、clear

作用很直观也很简单的一个成员函数，清楚字符串中所有有效字符，使其长度变为0

void StrTest11()
{//空间大小不变，长度变为0string s1 = "hello world";cout << s1 << endl;cout << s1.capacity() << endl;//15cout << s1.size() << endl;s1.clear();cout << s1.capacity() << endl;//15cout << s1.size() << endl;
}

二、empty

若有效字符个数为0，返回true，否则返回false

三、shrink_to_fit

void StrTest12() {string s1 = "hello world";cout << s1 << endl;s1.reserve(100);cout << s1.capacity() << endl;//111s1.shrink_to_fit();cout << s1.capacity() << endl;//还是15,储存在数组中
}

六、Modifiers(修改器)

6.1 oeprator+=

void StrTest13()
{string s1 = "hello,";string s2 = "xiaoyutongxue";s1 += s2;cout << s1 << endl;string s3 = "hello,";s3 += "xiaoyutongxue";cout << s3 << endl;string s4 = "ok";s4 += 'x';cout << s4 << endl;
}

6.2 append

void StrTest14()
{string s3 = "hello";string s4 = "world";char ch[] = "good";//添加字符串对象s3.append(s4); cout << s3 << endl;//添加字符串对象的一部分s3.append(s4, 1, 100);cout << s3 << endl;//添加字符数组s3.append(ch);cout << s3 << endl;///添加字符数组的n个字符s3.append(ch, 3);cout << s3 << endl;//追加常量字符串s3.append("66666");cout << s3 << endl;///追加n个字符xs3.append(15, 'x');cout << s3 << endl;//interatorstring s5 = "5月12日";string s6 = "mu qin jie kuai le!";s6.append(s5.begin(), s5.end());//左闭右开[ ),不用减一cout << s6 << endl;}

6.3 push_back

在串的尾部尾插一个字符c

6.4 assign

这些重载函数的参数都差不多，我就不再赘述了，直接代码呈现

void StrTest15()
{//用字符串对象覆盖string s1 = "hello world";cout << s1 << endl;string s2 = "xiaoyutongzhi";s1.assign(s2);cout << s1 << endl;//用一部分字符串对象覆盖s1.assign(s2, 6, 100);cout << s1 << endl;//用一个字符数组覆盖char ch[] = "mu qin jie kuai le";s1.assign(ch);cout << s1 << endl;//用字符数组的n个字符覆盖s1.assign(ch, 5);cout << s1 << endl;//迭代器覆盖s1.assign(s2.begin(), s2.end());cout << s1 << endl;
}

6.5 insert

void StrTest16() {string s1 = "hello ";string s2 = "xiaoyutongzhi";//s1.insert(6,s2);//cout << s1 << endl;//s1.insert(6, s2, 6, 100);//cout << s1 << endl;/*s1.insert(s1.end(), 6, 'x');cout << s1 << endl;*//*s1.insert(s1.end(),  'x');cout << s1 << endl;*/s1.insert(s1.end(), s2.begin(), s2.end());cout << s1 << endl; }

6.6 erase

void StrTest16() {string s1 = "hello ";string s2 = "xiaoyutongzhi";string s3 = "xiaoyutongzhi";s1.erase();cout << s1 << endl;cout << s1.capacity() << endl;cout << s1.size() << endl;s2.erase(6, 100);cout << s2 << endl;//删除p位置的内容s3.erase(s3.begin());cout << s3 << endl;s3.erase(s3.begin(), s3.end()-2);//左闭右开cout << s3 << endl;
}

注意：若pos位置大于字符串长度，则抛异常

6.7 replace

void StrTest1()
{string s1 = "xxxxxxxxxxx";cout << s1.size() << endl;string s2 = "cccccc";cout << s1 << endl;//1.类对象替换s1.replace(0, 3, s2);cout << s1 << endl;cout << s1.size() << endl;//说明会将从第0个位置开始，长度为三的字符替换，并追加s2剩余字符->size扩大//若len>字符串长度，默认替换到字符串尾//2.迭代器替换s1 = "xxxxxxxxxxx";s1.replace(s1.begin(), s1.begin()+2 , s2);cout << s1 << endl;cout << s1.size() << endl;//3.固定替换长度(类对象)s1 = "xxxxxxxxxxx";s1.replace(0, 3, s2, 0, 3);//若sublen大于len，则在替换的末尾追加cout << s1 << endl;cout << s1.size() << endl;//
}

6.8 swap

void StrTest2()
{//交换后，size和capacity(属性)也会交换string s1 = "xxxxxxxx";string s2 = "ssssssssssssssssssssss";cout << "s1 = " << s1 << endl;cout << "s1.size() = " << s1.size() << endl;cout << "s1.capacity() = " << s1.capacity() << endl;cout << "s2 = " << s2 << endl;cout << "s2.size() = " << s2.size() << endl;cout << "s2.capacity() = " << s2.capacity() << endl;s1.swap(s2);cout << "s1 = " << s1 << endl;cout << "s1.size() = " << s1.size() << endl;cout << "s1.capacity() = " << s1.capacity() << endl;cout << "s2 = " << s2 << endl;cout << "s2.size() = " << s2.size() << endl;cout << "s2.capacity() = " << s2.capacity() << endl;
}

6.9 pop_back

七、 String operations:

7.1 c_str

void STRTest1()
{//1.c_str函数string s = "hello world";//返回一个与s中存储的字符串相同的常量字符串，最后还有'\0'char* str = new char[s.length() + 1];//strcpy(str, s);这里直接用s是不行的，因为s是对象名，而不是一个char*strcpy(str, s.c_str());//这样就可以，返回一个常量字符串cout << s.c_str() << endl;cout << str << endl;delete[] str;str = nullptr;}

7.2 copy

void STRTest2()
{string s = "hello world";char str[20];int length = s.copy(str, 3, 0);//这里若是不把str的length处设置为'\0',下面打印就打印未初始化的随机值str[length] = '\0';cout << str << endl;cout << length << endl;}

7.3 find

void STRTest3()
{string s = "hello worldho";string s1 = "world";char s2[5] = "ld";size_t pos1 = s.find('h', 0);cout << pos1 << endl;size_t pos2 = s.find('o', 1);cout << pos2 << endl;size_t pos3 = s.find(s1, 0);cout << pos3 << endl;size_t pos4 = s.find(s2, 0);cout << pos4 << endl;
}

7.4 rfind

void STRTest4()
{string s1 = "hehello heorange hehe";string s2 = "he";size_t pos1 = s1.rfind('o',1110);size_t pos2 = s1.rfind(s2,1110);cout << pos1<<endl;cout << pos2 << endl;
}

7.5 find_first_of

void STRTest5()
{string s1 = "hello world hehe haha orange";size_t pos = s1.find_first_of("wld", 0);cout << pos << endl;//此处找到l下标为2//也可以把指定元素的字符全部改为*std::size_t found = s1.find_first_of("aeiou");while (found != std::string::npos){s1[found] = '*';found = s1.find_first_of("aeiou", found + 1);}std::cout << s1 << '\n';
}

7.6 substr

void STRTest6()
{//用find如何提取协议、域名和资源string s1 = "https://gitee.com/chen-1/qi-training-record";size_t pos1 = s1.find(':');size_t pos2 = s1.find('/', pos1 + 3);size_t pos3 = s1.find('/', pos2 + 1);cout << s1.substr(0, pos1-0)<<endl;//左闭右开，右边减去左边是元素个数cout << s1.substr(pos1+3, pos2-pos1-3)<<endl;//取出第二段cout << s1.substr(pos2 + 1) << endl;//取出第三段
}

八、非成员函数

8.1 operator+

void STRTest7() {string s1 = "hello";string s2 = "world";string s3 = s1 + s2;cout << s3 << endl;string s4 = s1 + "xxxxxx";cout << s4 << endl;//这就是为什么要写成全局函数而不写成成员函数的原因->要支持非对象成为第一个参数string s5 = "xxxxx" + s1;cout << s5 << endl;//不能是string s5 = "xxxx"+"xxxx"; 不能对内置类型进行运算符重载，至少要有一个自定义类型
}

8.2 string类同样支持比较(用ASCLL比较)

注意:运算符优先级流插入大于比较符号，注意加括号

8.3 getline

可以从流中读取空格(cin就不行)，读入str中

cin默认空格或换行是多个值之间的分割

getline默认换行是多个读入值之间的分割，也可以控制分隔符delim

九、其他函数

9.1 to_string、stoi

void STRTest8()
{int x = 0, y = 90;cin >> x >> y;string s = to_string(x + y);cout << s << endl;//stoi 字符串转成整形int ret = stoi(s);cout << ret << endl;
}