String, vector, stringvector

String, vector, stringvector

1. String object
1. string s;
S. size ();

// Returns the number of characters in s, which is also the length of s;

// The string object does not end with a NULL Character

// Size () returns the string: size_type, that is, the unsigned type, instead of the int type.
2. Add two string objects

The "+" operator is overloaded in the string standard library;

String s1 ("holo ");

String s2 ("world ");

String s3 = s1 + s2; // OK

Note that at least one of the left and right operands of the + operator must be of the string type:

String s4 = "hello" + "world ";//Error:No string operand

String s5 = s1 + "," + "world ";//OK

String s6 = "hello" + "," + s2 ;//Error

 

Ii. Standard Library vector type
1. Definition and initialization of a vector object

Several Methods for initializing a vector object
Vector <T> v1;	Objects whose vector type is T are saved. Default constructor, v1 is empty
Vector <T> v2 (v1 );	V2 is a copy of v1.
Vector <T> v3 (n, I );	V3 contains n elements whose values are I.
Vector <T> v4 (n );	V4 contains n copies of elements whose values are initialized

 

Vector <int> ivec;

Vector <sales_item> Sales_vec;

 

Although memory can be pre-allocated to the vector object of the number of given elements, a more effective method is to initialize an empty vector object and then dynamically add elements. (The vector is similar to the array, but the array cannot dynamically add elements, and it is worth noting that the vector subscript operation does not add elements, which is discussed in the following 3)

 

2. The size of the vector object

The size function of the vector object returns the size_tyoe value defined by the corresponding vector class, but it is worth noting that when using the size_type type, it must be pointed out where the type is defined. The vector type always includes the element type of the vector:

Vector <int>: size_type// OK

Vector: sizet_ype// Error

3. No element is added for the subscript operation.

# Include <iostream>

# Include <vector>

Using std: cin;

Using std: cout;

Using std: endl;

Using std: vector;

Int main (){
Vector <int> ivec; // empty vector
// For (vector <int >:: size_type I = 0; I! = 10; ++ I)
// Ivec [I] = I;

/*Try to insert 10 elements into ivec, And the element values are integers 0-9 in sequence. However, the ivec here is an empty vector object, and the subscript can only obtain existing elements. */

For (vector <int >:: size_type I = 0; I! = 10; ++ I)
Ivec. push_back (I );// Add an element whose value is t at the end of push_back (t)
For (vector <int >:: size_type I = 0; I! = Ivec. size (); ++ I)
Cout <ivec [I] <"";
Cout <endl;

Return 0;
}

It is very important to use the subscript operator [] to extract only existing elements. Attempts to subscript nonexistent elements are common errors during programming and may cause program crashes.