Bug STL string

STL

What is? STL

STL(standard template libaray- Standard template library )：== yes C++ An important part of the standard library ==, Not just a reusable component library , and == It is a software framework including data structure and algorithm ==

STL edition

The original version

Alexander Stepanov、Meng Lee The original version completed in HP Labs , In the spirit of open source , They declared that anyone was allowed to use 、 Copy 、 modify 、 spread 、 Business uses these codes , There is no need to pay . The only condition is that it needs to be used as open source as the original version . HP edition – all STL The ancestor of the implementation version

P. J. edition

from P. J. Plauger Development , Inherited from HP edition , By Windows Visual C++ use , Cannot disclose or modify , defects ： Low readability , The symbol naming is weird

RW edition

from Rouge Wage Companies to develop , Inherited from HP edition , By C+ + Builder use , Cannot disclose or modify , The readability is average .

SGI edition

from Silicon Graphics Computer Systems,Inc Companies to develop , Inherited from HP edition Ben . By GCC(Linux) use , Good portability , It can be made public 、 Modify or even sell , From naming style and programming In style , Reading is very high .== We learn from the back STL To read part of the source code , The main reference is this version .==

STL Six components of

How to learn STL

Just to summarize ：

== Study STL The three realms of ：==

1. It works ,
2. sensible ,
3. Can expand .

== Before you enter the company, you should be familiar with the first two levels of cultivation , The third layer is cultivated in the company ==

STL The defects of

1. STL The update of the library is too slow . Make complaints about this. , The last edition was reliable C++98, In the middle of the C++03 Some basic revisions .C++11 Out
   It's been a long time 13 year ,STL To further update .
2. STL Thread safety is not supported now . In the concurrent environment, we need to lock ourselves . And the granularity of the lock is relatively large .
3. STL Extreme pursuit of efficiency , It leads to internal complexity . Such as type extraction , Iterator extraction .
4. STL The use of will have the problem of code inflation , For example, use vector/vector/vector This will generate multiple copies of code , Of course, this is the template language
   Law itself .

The first container we will learn next is string

Why study string class ？

C Strings in languages

C In language , String is based on ’\0’ A collection of characters at the end , For ease of operation ,C The standard library provides some str Series of library functions , But these library functions are separate from strings , Not quite in line with OOP Thought , And the underlying space needs to be managed by users , If you don't pay attention, you may cross the border to visit

In the standard library string class

string class ( understand )

string Class documentation

1. A string is a class that represents a sequence of characters
2. The standard string class provides support for such objects , Its interface is similar to that of a standard character container , However, a design feature has been added specifically for manipulating single byte character strings .
3. string Class is to use char( As its character type , Use its default char_traits And distributor type ( More information about templates , see also basic_string).
4. string Class is basic_string An instance of the template class , It USES char To instantiate basic_string Template class , And use char_traits and allocator As basic_string Default parameters ( For more template information, please refer to basic_string).
5. Be careful , This class handles bytes independently of the encoding used : If used to handle multi byte or variable length characters ( Such as UTF-8) Sequence , All members of this class ( Such as length or size ) And its iterators , Will still be in bytes ( Not actually encoded characters ) To operate .

== summary ：==

1. string Is a string class that represents a string
2. The interface of this class is basically the same as that of a regular container , And added some special operations for string General operation of .
3. string At the bottom, it's actually ：basic_string Alias of template class ,typedef basic_string<char, char_traits, allocator>string;
4. Cannot manipulate sequences of multibyte or variable length characters .

In the use of string Class time , Must contain #include Header files and using namespace std;

string Class （ Note that I will only explain the most commonly used interfaces below ）

1.string Common constructions of class objects

(constructor) The name of the function	Functional specifications
string() （ a key ）	Construct empty string Class object , Empty string
string(const char* s) （ a key ）	use C-string To construct the string Class object
string(size_t n, char c)	string Class objects contain n Characters c
string(const string&s) （ a key ）	copy constructor

== learn STL, Focus on the most commonly used 30% Left and right interface functions , Others are rarely used , If one day we need to use , Just look at the documentation ==

int main(){	string s1;              // No arguments structure 	string s2("Hello c++"); // Structure with parameters 	string s3 = "Hello c++";// Direct construction of compiler optimization 	string s4(s2);          // Copy structure 	string s5(s4, 2, string::npos);    // Part of the structure 	string s6("123456789", 5);         // Pre tectonic n Characters 	// This function is if you want to write network code in the future , Intercepting the first few characters will use 	const char* url = "http://www.cplusplus.com/reference/string/string/string/";	string s7(url, 5);	string s8(10, 'x');     // structure n The same characters 	cout << s1 << endl;	cout << s2 << endl;	cout << s3 << endl;	cout << s4 << endl;	cout << s5 << endl;	cout << s6 << endl;	cout << s7 << endl;	cout << s8 << endl;	return 0;}

2.string Class object capacity operation

The name of the function	Functional specifications
size（ a key ）	Returns the valid character length of a string
length	Returns the valid character length of a string
capacity	Return the total size of the space
empty （ a key ）	Detection string released as empty string , Is to return true, Otherwise return to false
clear （ a key ）	Empty valid characters
reserve （ a key ）	Reserve space for Strings
resize （ a key ）	The number of valid characters should be n individual , Extra space with characters c fill

== actually length stay string Is the array length , and size equally , Then why two of them are the same , Because in history string Come out more than stl Good morning! ,string Documents on the official website are not classified into containers （ But he is the container ）, Instead, it is placed in the header file ,size It's common law ,length Is only used with string Of ==

Be careful ：

1. size() And length() The underlying implementation principle of the method is exactly the same , introduce size() The reason for this is to be consistent with the interfaces of other containers , In general, it's basically used size().
2. clear() Just to string Empty the valid characters in the , Don't change the size of the underlying space .
3. resize(size_t n) And resize(size_t n, char c) All are to change the number of valid characters in the string to n individual , The difference is that when the number of characters increases ：resize(n) use 0 To fill in the extra element space ,resize(size_t n, char c) Use characters c To fill in the extra element space . Be careful ：resize When you change the number of elements , If you increase the number of elements , It may change the size of the underlying capacity , If it is to reduce the number of elements , The total size of the underlying space remains unchanged .
4. reserve(size_t res_arg=0)： by string Reserve space , Do not change the number of effective elements , When reserve The parameter of is less than string The total size of the ground floor is ,reserver It doesn't change the size of the capacity .

== Here's a word at Function and [] It's the same , It can be considered that the early grammar may not support [] That's why at This interface replaces , The following supports ,at It's basically unnecessary , They are not exactly the same , It's different when they cross the border ==

==reserve Enough space can prevent multiple capacity additions , that resize Is that OK ==

== We can also see the results of the same code running on different platforms ==

int main(){	string s1 = "Hello world";	string s2 ="world";	// Determines if the string is empty 	cout <<"s1.empty "<< s1.empty() << endl;	cout << "s2.empty " << s2.empty() << endl;	// size 	cout << "s1.size " << s1.size() << endl;	cout << "s2.size " << s2.size() << endl;	// Capacity 	cout <<"s1.capacity "<< s1.capacity() << endl;	cout <<"s2.capacity "<< s2.capacity() << endl << endl;	// Clear all the data , Namely size Become zero , But space doesn't release 	s1.clear();	cout << "s1.size " << s1.size() << endl;	cout << "s1.capacity " << s1.capacity() << endl << endl;	// Insert... Into the object n Characters , The default character is ‘\0’	// If you want to put other characters 	s1.resize(15);	string s3 = s2;	s2.resize(1,'x');	s3.resize(16,'x');	cout <<"s2: "<< s2 << endl;	cout <<"s3: "<< s3 << endl;	cout << "s1.size " << s1.size() << endl;	cout << "s2.size " << s2.size() << endl;	cout << "s1.capacity " << s1.capacity() << endl;	cout << "s2.capacity " << s2.capacity() << endl << endl;	// Request a change in capacity  	s2.reserve(40);	cout << "s2: " << s2 << endl;	cout << "s2.size " << s2.size() << endl;	cout << "s2.capacity " << s2.capacity() << endl << endl;	string s4;	//// Give enough space directly to prevent multiple capacity increases  	//s4.reserve(127);	// have a look resize Can you prevent multiple capacity increases 	s4.resize(127);	int old_capacity = s4.capacity();	for (char ch = 0; ch < 127; ch++)	{		s4 += ch;		// Check the capacity increase 		if (old_capacity != s4.capacity())		{			cout << " increase capacity ：" << old_capacity <<"->"<< s4.capacity()<< endl;		}		old_capacity = s4.capacity();	}	cout << s4 << endl << endl;	return 0;}

3.string Class object access and traversal operation

The name of the function	Functional specifications
operator[] （ a key ）	return pos The character of position ,const string Class object call
begin+ end	begin Get an iterator of a character + end Gets the iterator at the next position of the last character
rbegin + rend	begin Get an iterator of a character + end Gets the iterator at the next position of the last character
Range for	C++11 Support more concise scope for New traversal method

== iterator ==

== Iterator meaning ： image string,vector Support [] Traverse , however list,map Wait, the container does not support [], We're going to iterate through , So iterators are a uniform way to use them ==

int main(){	string s1 = "Hello c++";	// iterator 	string::iterator it = s1.begin();//begin Is an iterator that returns the start position 	while (it != s1.end())//end Is an iterator that returns the end position 	{		static char tmp = 'a';		*it++ = tmp++;	}	it = s1.begin();	while (it != s1.end())//end Is an iterator that returns the end position 	{		cout << *it << " ";		it++;			}	return 0;}

== reverse iterator ==

int main(){	string s1 = "Hello c++";	// reverse iterator 	string::reverse_iterator rit = s1.rbegin();	while (rit != s1.rend())	{		cout << *rit << " ";		rit++;	}	return 0;}