Use of strings in C + +

When we start using the C language to handle strings, we get a lot of trouble. The C language lacks the corresponding string handler function, and if you want to implement a string function, we can do it by ourselves. But when it comes to C + +, the processing of strings becomes surprisingly simple. Today, let's learn about the highest-frequency string-handling functions in C + +. The sample code is uploaded to: https://github.com/chenyufeng1991/CppString.

The first step is to introduce a string header file in C + +:

#include <string>

Please note that the header file here is not. h, otherwise it becomes the header file in C language.

(1) Creating a string

There are several ways to create a string, and the most typical way is to use a copy constructor.

String str ("Chenyufeng", 3);  cout << str << Endl;

cout copies the most recent 3-character string at the beginning of the original string. The result of the printing is Che.

String str2 ("Chenyufeng", 2,3);  cout << str2 << Endl;

cout copies the most recent 3-character string at the beginning of the original string index=2. The print result is eny.

=: string Assignment  str2 = "Robert";  cout << str2 << Endl;

It is also possible to assign a value string to a variable in the form of a direct assignment, using "=". Print the result to Robert.

(2) Swap: Swap the value of two strings

Swap: Swap the value of two strings string    string1 = "Chen";     String string2 = "Yufeng";     Swap (string1, string2);     cout << "string1 =" << string1 << "string2 =" << string2 << Endl;

The printed result is already swapped with the value of the original string.

(3) +,append: Adding a string

+ =, append: Adds string     stringorigin = "Chen" at the tail      ; String stringappend = "Yufeng";      Stringorigin = Stringorigin + stringappend;      cout << "Stringorigin =" << stringorigin << Endl;        Stringorigin.append ("_ok");      cout << "stringoriginappend =" << stringorigin << Endl;

Note that adding a string operation modifies the original string. It is convenient to add the string directly using the + sign.

(4) Insert: Inserts a string at the specified position

Insert: Inserts string    stringinsertorigin = "Chenyufeng" in the specified position;      Stringinsertorigin.insert (3, "__");      cout << "Stringinsertorigin =" << stringinsertorigin << Endl;

The above code can be inserted in the indx=3 position __ underline, the printing result is Che__nyufeng.

(5) Erase,clear Delete string

Erase: Delete character   string stringeraseorigin = "Chenyufeng";     Stringeraseorigin.erase ();     cout << "Stringeraseorigin =" << stringeraseorigin << Endl;         Clear: Remove all characters    string stringclearorigin = "Chenyufeng";     Stringclearorigin.clear ();     cout << "Stringclearorigin =" << stringclearorigin << Endl;

In fact, all of this is to empty the string.

(6) Replace: replace string

Replace: Replaces a string with a size character at the beginning of a POS position replaced by the string     Stringreplaceorigin = "Chenyufeng";      Stringreplaceorigin.replace (3, 2, "the");      cout << "Stringreplaceorigin =" << stringreplaceorigin << Endl;

The code above replaces the string 2 characters starting with index=3 with "66" and prints the result as Che66ufeng.

(7) = =,, =: Compare string size

Using this operator to manipulate strings in C + + is in fact an operator overload. The string comparison size is based on the dictionary order of the alphabet, or the ASCII value in sequential comparison of the size. Until a different letter of two strings is compared or the last stop of a string is compared.

==,<,>,<=,>=: Comparing strings string    stringleft = "Zhen";     String stringright = "Yufeng";     if (Stringleft = = stringright)     {         cout << "equal" << Endl;     }       if (stringleft! = stringright)     {         cout << "Not Equal" << Endl;     }       if (Stringleft < stringright)     {         cout << "Stringleft < stringright" << Endl;     }       if (Stringleft > Stringright)     {         cout << "Stringleft > Stringright" << endl;     }

(8) Size,length: Calculating string Lengths

The length of the computed string here is different from the C language, not including the end, and calculates the true length.

Size (), Length (): Calculates the string length string     stringcount = "Chenyufeng";      cout << "stringsize =" << stringcount.size () << Endl;      cout << "stringlength =" << stringcount.length () << Endl;

The above print results are all 10.

(9) Empty: Determine if the string is empty

Empty (): Determines whether the string is empty string    stringisempty = "";      String stringnotempty = "Chen";      if (Stringisempty.empty ())      {          cout << "stringisempty = = Empty" << Endl;      }      else      {          cout << "Stringisempty! = Empty" << Endl;      }        if (Stringnotempty.empty ())      {          cout << "stringnotempty = = Empty" << Endl;      }      else      {          cout << "Stringnotempty! = Empty" << Endl;      }

(10) input and output stream of string

Input output stream    cout << "Please enter a string" <<endl;      string Stringinput;      Cin >> Stringinput;      cout << "stringinput =" << stringinput << Endl;

A string can also use an input-output stream similar to other C + + data types. You can use the ENTER key to end the input stream.

(one) Max_size: The maximum number of strings that can be accommodated.

Max_size:    string stringmaxsize;      cout << "stringmaxsize =" << stringmaxsize.max_size () << Endl;

The result is: 18446744073709551599. Indicates that the string can hold so many characters.

[], at: element access and modification

[],at (): element access    string Stringat = "Chenyufeng";      cout << "stringat[3] =" <<stringat[3 "<< Endl;      cout << "stringat.at (3) =" << stringat.at (3) << Endl;        STRINGAT[3] = ' 6 ';      stringat.at (5) = ' 9 ';      cout << "Stringat =" << stringat << Endl;

Strings can be manipulated as well as arrays, accessed using subscripts, and can be modified with the original string.

Compare: string comparison, return 0,1,-1.

Compare ()     string stringcompare = "Chenyufeng";      int AAA = Stringcompare.compare ("Chen"); > 0      int bbb = Stringcompare.compare ("Chenyufeng");//= = 0      int CCC = Stringcompare.compare ("Done");//< 0      cout << "AAA =" << aaa << "; bbb =" << bbb << "; CCC =" << CCC << Endl;

(+) Substr: Take substring

substr     String stringsubstr = "Chenyufeng";     3 characters starting from index 4     cout << "Stringsubstr.substr (4,3) =" << stringsubstr.substr (4,3) << Endl;       All characters starting from index 4    cout << "Stringsubstr.substr (4) =" <<stringsubstr.substr (4) << Endl;       The entire character    cout << "stringsubstr.substr () =" <<stringsubstr.substr () << Endl;

() find: Find a character

Find     string stringfind = "Chenyufeng";      Stringfind.find (' n ');      cout << "Stringfind.find (' n ') =" << stringfind.find (' n ') << Endl;        cout << "stringfind.find_first_of (' e ') =" << stringfind.find_first_of (' e ') << Endl;            cout << "stringfind.find_last_of (' e ') =" << stringfind.find_last_of (' e ') << Endl;

The default find function is the subscript index that returns the first occurrence of a character. Find_first_of and Find_last_of are the first and last occurrences of the index of a character.

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