当前位置：网站首页>First acquaintance with string+ simple usage (I)

string It's a class
string Class is basic_string An instance of the template class
Use char To instantiate basic_string Template class
The instantiated object is an array of characters that manages dynamic growth , With ‘\0’ ending
You need to include the header file when using string
#include <string>

c++98 in string Common constructors

1. Construct an empty class object -- An empty string
string + ( Object name )
string s1;
2. Constant string initialization

string + Object name (“ initialization ”)
string s2("hello csdn");
3. Copy structure initialization
string + Object name ( Object already exists )
string + Object name = Object already exists
string s3(s2);
string s4 = s3;
The above three are the most commonly used initialization methods
4. Specified length initialization .
string + Object name (" Initialize content , Initialization length ")
string s5("asdfghjkl", 4);
5. Specify the characters and their number to initialize
string + Object name ( Number , character )
string s6(5,'c');
6. Initializes the substring of an existing object
string + Object name ( Object already exists , Specify starting position , Specify the length )
string s7(s2,3,5);

string Assignment

1. object 1= object 2

2. object = character string
3. object = character

string Object traversal

1.[ Subscript ] Traverse
void test3()
{
	string s1("abcdefg");
	//1.[ Subscript ] Traverse 

	// It's used here size() function , The length of the string is returned , It doesn't contain \0
	cout << s1.size() << endl;

	for (size_t i = 0;i < s1.size();i++)
	{
		// Here we use [], It's essentially function overloading : s1.operator[](i);
		cout << s1[i] << " ";
	}
	cout << endl;
}
string Class is a custom type , use [] You need to find its operator overloaded function to call
2. Iterator forward traversal
void test4()
{
	string s1("abcdefg");
	//2. Iterator traversal --iterator Belong to string A built-in type in 
	
	// This method can be used to solve some problems with large number of combinations 
	string::iterator it = s1.begin();
	
	//end() Is the next position of the end position 
	while (it!=s1.end())
	{
		cout << *it << " ";
		it++;
	}
	cout << endl;
}
We're just getting started with iterators , It can be understood as a pointer first ,begin() Point to the first character ,end() Points to the next... Of the last character , Generally point to '\0', The next step is to operate in pointer mode .

3. Iterator traverses backwards
void test7()
{
	string s1("abcdefg");
	//3. Iterator traverses backwards --reverse_iterator

	// This method can be used to solve some problems with large number of combinations 
	string::reverse_iterator rit = s1.rbegin();

	//end() Is the next position of the end position 
	while (rit != s1.rend())
	{
		cout << *rit << " ";
		rit++;
	}
	cout << endl;
}
The direction of traversal is opposite to that of the forward iterator , Pay attention to the grammatical form ,reverse_iterator、rbegin、rend
Although it is a reverse traversal , But still ++, No --

4. Range for
void test5()
{
	//3. Range for Traverse 
	string s1("hello csdn");
	for (auto e:s1)
	{
		cout << e << " ";
	}
	cout << endl;
}
Create a variable e, according to s1 use auto Introduction e The type of , Ergodic time , automatically ++, Until I met '\0' end
Range for In the implementation of , Is actually replaced by an iterator

string Modification of

Now that you can traverse and access every character , The corresponding can also be used when accessing characters , Modify it
1. Subscript access modification

2. In access object at Function to modify

string Reference and reference

string Can be counted as a type , Parameters can be transferred
Here we directly transfer values and parameters , A formal parameter is a temporary copy of an argument
When the object is large , Consume large , therefore Formal parameter application reference passes parameter
Do not change the parameter content , Try to add const

add const Then you can't run through it , because begin and end There is a problem of permission amplification when returning

To solve the problem of making permissions the same , Then the iterator type should be const, The changes are as follows ：

string The capacity of the object

string Type supports viewing the size and capacity of objects
Capacity
Call the object's capacity() function , You can view the capacity

But each dynamic development will increase the consumption , Is there any way to reduce the number of open space ？
reserve
Just change the size of the space , Yes size No impact

resize

string End insert of object

Insert characters push_back
Usage is as follows ：
Insert string append
Two ways of using ： Insert the string directly 、 Insert string Class object
direct +=
Support for characters and strings , Is the most widely used