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This article mainly introduces the C++ string class example analysis, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

Preface

The string class is the template class instantiated from the basic_string template in STL. It is defined as follows:

Typedef basic_string string

Basic_string, you don't have to dig into it here.

There are many member functions of the string class, and functions with the same name often have five or six overloaded versions. Due to the limitation of space, these prototypes cannot be listed and explained one by one. Here, only the common member functions are classified by function, and the application examples are given directly. Through the examples, the reader can basically grasp the usage of these member functions.

To learn more about the string classes, read the C++ reference manual or the online materials that come with the compiler. For the content of string processing described earlier, I will not repeat it here.

1. Constructor function

The string class has several constructors, and examples of usage are as follows:

String S1 (); / / si = "" string S2 ("Hello"); / / S2 = "Hello" string S3 (4,'K'); / / S3 = "KKKK" string S4 ("12345", 1,3); / / S4 = "234", that is, a substring of "12345" with length 3 starting from subscript 1

For ease of addressing, a string of length m starting with the string subscript n is called "substring (n, m)" later in this tutorial.

The string class does not receive a constructor for an integer parameter or a character parameter. The following two ways are wrong:

String S1 ('K'); string S2 (123)

two。 Assign a value to a string object

You can assign values to string objects with variables and constants of type char*, and variables and constants of type char. For example:

String S1: S1 = "Hello"; / / S1 = "Hello" S2 = 'Knights; / / S2 = "K"

The string class also has assign member functions that can be used to assign values to string objects. The assign member function returns a reference to the object itself. For example:

String S1 ("12345"), S2TX S3.Qing (S1); / S3 = s1s2.assign (S1, 1,2); / S2 = "23", that is, the substring of S1 (1,2) s2.assign (4,'K'); / S2 = "KKKK" s2.assign ("abcde", 2,3); / / S2 = "cde", that is, the substring of "abcde" (2,3)

3. Find the length of the string

The length member function returns the length of the string. Size member functions can achieve the same function.

4. Concatenation of strings in string object

In addition to using the + and + = operators to perform string concatenation operations on string objects, the string class has append member functions that can be used to add content to the end of the string. The append member function returns a reference to the object itself. For example:

String S1 ("123"), S2 (" abc "); s1.append (S2); / S1 =" 123abc "s1.append (S2, 1,2); / S1 =" 123abcbc "s1.append (3,'K'); / S1 =" 123abcbcKKK "s1.append (" ABCDE ", 2,3); / S1 =" 123abcbcKKKCDE ", add a substring of" ABCDE "(2,3)

5. Comparison of string objects

In addition to comparing string objects with operators, the string class has compare member functions that can be used to compare strings.

The compare member function has the following return value:

Less than 0 indicates that the current string is small

Equal to 0 means that two strings are equal.

A value greater than 0 indicates that another string is small.

For example:

String S1 ("hello"), S2 ("hello, world"); int n = s1.compare (S2); n = s1.compare (1Lecture 2, s2,0score3); / / compare the substrings of S1 (1L2) and the substrings of S2 (0L2) n = s1.compare (0L2, S2); / / compare the substrings of S1 (0L2) with s2n = s1.compare ("Hello"); n = s1.compare (1L2, "Hello") / / compare the substrings of S1 (1Magne2) and "Hello" n = s1.compare (1Magne2, "Hello", 1Magin2); / / compare the substrings of S1 (1Magne2) and the substrings of "Hello" (1Magne2)

6. Find the substring of the string object

The substr member function can be used to find the substring (n, m). The prototype is as follows:

String substr (int n = 0, int m = string::npos) const

When called, if the omission of m or m exceeds the length of the string, the resulting substring is the part from the subscript n to the end of the string. For example:

String S1 = "this is ok"; string S2 = s1.substr (2,4); / / S2 = "is I" S2 = s1.substr (2); / / S2 = "is is ok"

7. Exchange the contents of two string objects

The swap member function can exchange the contents of two string objects. For example:

String S1 ("West"), S2 ("East"); s1.swap (S2); / / S1 = "East", S2 = "West"

8. Find substrings and characters

The string class has some member functions that find substrings and characters, and their return values are the position of the substring or character in the string object string (that is, the subscript). If it cannot be found, string::npos is returned. String:: npos is a static constant defined in the string class. These functions are as follows:

Find: look for the location where the substring or character appears after going.

Rfind: looks for the location of a substring or character from back to front.

Find_first_of: find out where the character contained in another string appears after going. For example:

S1.find_first_of ("abc"); / / find the position where any character in "abc" appears for the first time in S1

Find_last_of: look from back to front to find out where the characters contained in another string appear.

Find_first_not_of: look for a character that is not contained in another string after going.

Find_last_not_of: look from back to front to find out where there are characters that are not contained in another string.

The following is a sample program for finding member functions for the string class.

# include # include using namespace std;int main () {string S1 ("Source Code"); int n; if ((n = s1.find ('u'))! = string::npos) / / find the location of u cout

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