C++ Strings

In C++, string class that represents sequence of characters is used to store string values. We can perform many operations on strings such as concatenation, comparison, conversion etc.

The string header must first be included before a string can be declared . The standard namespace can also be included since the string class is part of that namespace.

#include 
using namespace std;

String Declaration

A string can then be declared like any other data type. To assign a string value to a string variable, enclose the literals by double quotes and assign them to the variable. You can also assign a initial value through constructor initialization at the same time as the string is declared.

string h = "Hello";
string w (" World");

Let's see the simple example of C++ string.

#include <iostream>
using namespace std;
int main( ) {
    string s1 = "Hello";  
        char ch[] = { 'C', '+', '+'};  
        string s2 = string(ch);  
        cout<<s1<<endl;  
        cout<<s2<<endl;  
}

Combining Strings

We can combine two strings using the plus sign, known as the concatenation operator (+). It has an accompanying assignment operator (+=) to append a string .

string a = h + w; // Hello World
h += w; // Hello World

The concatenation operator will work as long as one of the strings it operates on is a C++ string.

string b = "Hello" + w; // ok

It is not able to concatenate two C strings or two string literals. To do this, one of the values has to be explicitly cast to a string.

char *c = "World"; // C-style string
b = (string)c + c; // ok
b = "Hello" + (string)" World"; // ok

String literals will also be implicitly combined if the plus sign is left out.

b = "Hel" "lo"; // ok

Escape Characters

A string literal can be extended to more than one line by putting a backslash sign (\) at the end of each line.

string s = "Hello \ World";

To add a new line to the string itself, the escape character “\n” is used.

s = "Hello \n World";

This backslash notation is used to write special characters, such as tab or form feed characters.

Additionally, any one of the 128 ASCII characters can be expressed by writing a backslash followed by the ASCII code for that character, represented as either an octal or hexadecimal number.

"\07F" // octal character (0-07F)
"\0x177" // hexadecimal character (0-0x177)

As of C++11, escape characters can be ignored by adding a “R” before the string along with a set of parentheses within the double quotes. This is called a raw string and can be used, for instance, to make file paths more readable.

string escaped = "c:\\Windows\\System32\\cmd.exe";
string raw = R"(c:\Windows\System32\cmd.exe)";

Comparing Strings

To compare two strings simply use the equal to operator (==). This will not compare the memory addresses of the strings, as is the case of C strings.

string s = "Hello";
bool b = (s == "Hello"); // true

String Encodings

A string enclosed within double quotes produces an array of the char type, which can only hold 256 unique symbols. To support larger character sets the wide character type wchar_t is provided. To create this type of string literals prepend the string with a capital "L". The resulting array can be stored using the wstring class. This class works like the basic string class but uses the wchar_t character type instead.

wstring s1 = L"Hello";
wchar_t *s2 = L"Hello";

Fixed-size character types were introduced in C++11, namely char16_t and char32_t. These types provide definite representations of the UTF-16 and UTF-32 encodings respectively. UTF-16 string literals are prefixed with “u” and can be stored using the u16string class. Likewise, UTF-32 string literals are prefixed with “U” and are stored in the u32string class. The prefix “u8” was also added to represent a UTF-8 encoded string literal.

string s3 = u8"UTF-8 string";
u16string s4 = u"UTF-16 string";
u32string s5 = U"UTF-32 string";

Specific Unicode characters can be inserted into a string literal using the escape character “\u” followed by a hexadecimal number representing the character.

String Functions

C++ supports a wide range of functions that manipulate strings. The most common are given below.

Let's see the simple example of string comparison using strcmp() function.

#include 
#include <cstring>
using namespace std;
int main ()
{
  char key[] = "mango";
  char buffer[50];
  do {
     cout<<"What is my favourite fruit? ";
     cin>>buffer;
  } while (strcmp (key,buffer) != 0);
 cout<<"Answer is correct!!"<<endl;
  return 0;
}

Let's see the simple example of string concatenation using strcat() function.

#include <iostream>
#include <cstring>
using namespace std;
int main()
{
    char key[25], buffer[25];
    cout << "Enter the key string: ";
    cin.getline(key, 25);
    cout << "Enter the buffer string: ";
     cin.getline(buffer, 25);
    strcat(key, buffer); 
    cout << "Key = " << key << endl;
    cout << "Buffer = " << buffer<<endl;
    return 0;
}

Let's see the simple example of copy the string using strcpy() function.

#include <iostream>
#include <cstring>
using namespace std;
int main()
{
    char key[25], buffer[25];
    cout << "Enter the key string: ";
    cin.getline(key, 25);
    strcpy(buffer, key);
    cout << "Key = "<< key << endl;
    cout << "Buffer = "<< buffer<<endl;
    return 0;
}

Let's see the simple example of finding the string length using strlen() function.

#include <iostream>
#include <cstring>
using namespace std;
int main()
{
    char ary[] = "Welcome to C++ Programming";
    cout << "Length of String = " << strlen(ary)<<endl;
    return 0;
}