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;

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;

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) ==,<, <=, >=: Comparing string sizes

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, and is not included at the end of the, the calculation is 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;

Printing results are: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.

The above 15 C + + string processing functions are the most common, of course, there are many others, I will continue to add in the subsequent use. String is actually part of the STL. The use of String functions is more specific to the official document: Http://en.cppreference.com/w/cpp/string/basic_string.

Use of strings in C + +