Chapter 3 C++: String, vector, and array

Chapter 2 introducesBuilt-in types, this chapter introducesAbstract data type library.

- Among them, string and vector are the two most important standard library types. The former supports variable-length string, The latter represents a variable-length collection.
- Another standard library type is iterator, which is a supporting type of string and vector and is often used to access characters in string and elements in vector.

Chapter 3 Strings, Vectors and Arrays

• Header files should not contain using statements.

Standard library type string

#include <string>using std::string

• Initialization string

• Direct initialization (direct initialization)

• Copy initialization (copy initialization): use the equal sign
  

  string s1;string s2(s1);string s2 = s2;string s3("hiya");string s3 = "hiya";string s4(10, 'c'); //s4的内容是cccccccccc

• Operations on string objects

  1. cout << s2. cin >> s         //将string对象读入s，遇到空白停止3. getline(is, s)   //从输入流is中读取一行赋给s（换行符被读取了，但被丢弃而没有赋给s），返回is4. s.empty()        //s为空返回true，否则返回false5. s.size()6. s[n]             //返回s中第n个字符的引用，位置n从0计起          
  7. s1 + s2          //返回s1和s2连接后的结果8. s1 = s29. s1 == s210. s1 != s211. <, <=, >, >=

• Logical NOT operator (!)

• string::size_type type: The return value type of s.size() is the supporting type of the string class. It is an unsigned type value that can store the size of any string object.

• Processing characters in string objects

• cctype header file: function for judging or processing single characters

  isupper(c)      //c是大写字母时为真islower(c)tolower(c)      //如果c是大写字母，则输出对于的小写字母；否则原样输出toupper(c)isalpha(c)      //c是字母时为真isdigit(c)      //c是数字时为真isalnum(c)      //c是字母或数字时为真ispunct(c)      //c是标点符号时为真isspace(c)      //c是空白时为真（即c是空格、横向制表符、纵向制表符、回车符、换行符、进纸符的一种）iscntrl(c)      //c是控制字符时为真isgraph(c)      //c不是空格但可打印时为真isprint(c)      //c是可打印字符时为真（即c是空格或具有可视形式）isxdigit(c)     //十六进制数

• Use the C version of the C standard library header file, in the shape of name.h. These files in C are named cname, with the same content, and the names defined in the header file cname belong to the namespace std.

• Range for（range for）statement

for (declaration : expression)
    statement

例如：string str("some string");//每行输出str中的一个字符for(auto c : str)    cout << c <<endl;

Standard library type vector

vector is a class template (class template). A vector represents a collection of objects, all of which are of the same type. Each object in the collection has a corresponding index, which is used to access the object. Vector is also often called container (container).

• Definition and initialization of vector objects

vector<T> v1vector<T> v2(v1)vector<T> v2 = v1vector<T> v3(n, val)vector<T> v4(n)vector<T> v5{a,b,c...}vector<T> v5 = {a,b,c...}

• List initialization vector object

vector<string> articles = {"a", "an", "the"};

• Add elements to the vector object

  The exact number in the vector object is not known until runtime:

  string word;vector<string> text;while (cin >> word) {
      text.push_back(word);
  }

• Vector objects can grow efficiently: Vector can add elements efficiently and quickly at runtime.

• If the loop body contains statements that add elements to the vector object, you cannot use the range for loop.

• push_back: Treat a value as the tail element of the vector object and "push" it to the "tail end (back)" of the vector object.
  

  vector<int> v2;for(int i=0; i != 100; ++1)
      v2.push_back(i);

• Other vector operations

v.empty()
v.size()
v.push_back(t)
v[n]        //返回v中第n个位置上元素的引用v1 = v2v1 = {a,b,c...}v1 == v2v1 != v2
<, <=, >, >=

Iterator iterator

A general mechanism: implementation Use the subscript operator to access characters of a string object or elements of a vector object.

Similar to pointer types, it provides indirect access to objects.

• begin and end members

  //由编译器决定b、e的类型//b表示v的第一个元素，e表示v尾元素的下一个元素auto b = v.begin(), e = v.end();    //b、e类型相同

• The iterator returned by the end member is often called the tail iterator ( off-the-end iterator), or tail iterator for short.

• If the container is empty, begin and end return both tail iterators.

• Standard containerIterator operator

*iter           返回迭代器iter所指元素的引用iter->men       解引用iter并获取钙元素的名为mem的成员，等价于（*iter）.mem++iter--iteriter1 == iter2iter1 != iter2

rrree

• # Iterator type

The standard library with iterators uses iterator and const_iterator to represent the type of iterator:

//将字符串首字母改成大写string s("some string");if (s.begin() != s.end()) {    auto it = s.begin();
    *it = toupper(*it);
}//将迭代器从一个元素移动到另一个元素，把字符串中第一个单词改为大写//注意，使用的是!=，而不是<for(auto it = s.begin(); it != s.end() && !isspace(*it); ++it)
    *it = toupper(*it);

Reference: C Primer Fifth Edition

Chapter 2 IntroductionBuilt-in types, this chapter introduces Abstract data type library
. - Among them, string and vector are the two most important standard library types. The former supports variable-length strings, and the latter represents Variable-length collection
. - Another standard library type is iterator

, which is a supporting type of string and vector and is often used to access characters in string and elements in vector.

Related articles:

Chapter 1 C: Function return value, GNU compiler command

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Chapter 2 C: Variables and basic types

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