Strings in C++

We will learn how to work with strings in C++ in this article.

A string stores a sequence of characters. In C++, there are two types of strings:

1. C-style strings
2. Objects of the string class in the Standard C++ Library

C-style Strings

C++ continues to support C-style strings. Arrays are used to store a group of characters in C programming. C-style strings are 1-D char arrays with a null character ‘\0’ at the end.

1. Defining a C-style string

Syntax to declare a string:

char string_name[size];

Let’s initialize string str to store the word TechVidvan. This can be done in the following ways:

• char str[] = “TechVidvan”;
• char str[20] = “TechVidvan”;
• char str[] = {‘T’, ‘e’, ‘c’, ‘h’, ‘V’, ‘i’, ‘d’, ‘v’, ‘a’, ‘n’, ‘\0’};
• char str[11] = {‘T’, ‘e’, ‘c’, ‘h’, ‘V’, ‘i’, ‘d’, ‘v’, ‘a’, ‘n’, ‘\0’};

Example to read and display C-style string

#include <iostream>
using namespace std;

int main() {
  char word[20];
  char line[100];
  
  //read a word
  cout<<"Enter a word ";
  cin>>word;
  //display the word
  cout<<endl<<word<<endl;
  
  //read a line 
  cout<<"Enter a line ";
  cin.get(line, 100);
  //display the line
  cout<<endl<<line;
  
  return 0;
}

Output

Here, to read a line we used cin.get() function. It is used to read character arrays including whitespaces.
Syntax:

cin.get(string_name, size);

Object of std::string C++ class

In C++, we can represent strings as objects of std::string class. These objects are used to hold strings. The string class holds characters as a stream of bytes where we can access a single byte character.

Unlike character arrays, string objects do not have a fixed length and can be increased as needed.

Remember that to use string, we must include the <string> library as a header file in our code.

1. Defining a string object

Syntax to declare a string object:

string string_name;

Let’s initialize a string object,

string str = "TechVidvan";

Example to illustrate the use of string

#include <iostream>
#include <string>
using namespace std;

int main() {
  string s1;
  
  //taking input of a string from user
  getline(cin, s1);
  
  //displaying the string
  cout<<"Entered string is "<<s1;
  return 0;
}

Input
TechVidvan
Output

In the above example, we have used the getline() function to store the string entered by the user.

Some other functions to operate on strings

1. push_back() : We use this function to add a character at the end of a string.
Syntax:

string_name.push_back(‘character’);

2. pop_back() : We use this function to delete the last character of a string.
Syntax:

string_name.pop_back();

3. length() and size() : We use these functions to get the length of a string.
Syntax:

string_name.length();

Or

string_name.size();

Memory occupied by strings in C++

We know that data type char occupies 1 byte of memory space. A string in C++ thus occupies N bytes where, N = no. of characters in a string including the null character.

For example,

char s[ ] = "TechVidvan";

This string s will occupy (10 + 1) = 11 bytes of memory space. We can represent this in tabular form as shown below

While designing, instead of DATAFLAIR\0, it will be TECHVIDVAN\0 and index from 0 – 10.

We can use sizeof() operator to get the size of a string.

C++ Functions for strings

C++ offers various functions to operate on strings.

1. strcpy(string1, string2); : We use this function to copy string2 into string1.

2. strcat(string1, string2); : We use this function to concatenate both the strings.

3. strlen(string1); : We use this function to compute the length of a string.

4. strcmp(string1, string2); : We use this function to compare both the strings. It returns 0 when both are equal, <0 when string1<string2 and >0 when string1>string2.

5. strchr(string1, ch); : We use this function to get the pointer pointing to the first appearance of character ch in a string.

6. strrchr(string1, ch); : We use this function to get the pointer pointing to the last appearance of character ch in a string.

7. strstr(string1, string2); : We use this function to get the pointer pointing to the first appearance of string2 in string1.

8. strlwr(string1); : We use this function to convert all the characters of a string to lowercase.

9. strupr(string1); : We use this function to convert all the characters of a string to uppercase.

10. strncat(string1, string2, n); : We use this function to append first n characters of string2 at the end of string1.

11. strncpy(string1, string2, n); : We use this function to copy first n characters of string2 into string1.

12.strncmp(string1, string2, n); : We use this function to compare n characters of both the strings. It returns 0 when both are equal, <0 when  string1<string2 and >0 when string1>string2.

13. strcmpi(string1, string2); : We use this function to compare both the strings without considering case sensitivity. It returns 0 when both are equal, <0 when string1<string2 and >0 when string1>string2.

14. strnicmp(string1, string2, n); : We use this function to compare n characters of both the strings ignoring case sensitivity. It returns 0 when both are equal, <0 when string1<string2 and >0 when string1>string2.

15. strdup(string1); : We use this function to get a pointer to a duplicate string of string1.

16. strndup(string1, n); : This function works similar to strdup except, it duplicates n characters of string.

17. strset(string1, ch); : We use this function to set all characters of a string to character ch.

18. strnset(string1, ch, n); : We use this function to set first n characters of a string to character ch.

To use these functions we need to include <string.h> header file in our program.

Example to illustrate the use of some C++ string functions

#include <iostream>
#include <string.h>
using namespace std;

int main() {
  char s1[ ] = "TechVidvan";
  char s2[ ] = "DataFlair";
  
  int length = strlen(s1);
  cout<<"Length of string TechVidvan = "<<length<<endl;
  
  char s3[15];
  strcpy(s3, s1);
  cout<<"Copied string = "<<s3<<endl;
  
  strcat(s1,s2);
  cout<<"Concatenated strings = "<<s1<<endl;
  
  if(strcmp(s1,s2)==0)
      cout<<"Strings are equal";
  else
      cout<<"Strings are unequal";
  
  return 0;
}

Output

Passing string to a function

Example of strings as function parameters

#include <iostream>
#include <string>
using namespace std;

void print(char s[], string str) {
    cout<<"Entered C-style string is "<<s<<endl;
    cout<<"Entered string object is "<<str;
}
int main() {
  char s1[50] = "TechVidvan";
  string s2 = "Data Flair";
  
  print(s1, s2);
  
  return 0;
}

Output

Summary

In this article, we have learnt about strings in C++. A string is a sequence of characters. C++ offers us two types of strings, one in the form of character arrays and other as objects of std::string class. We discussed how to work with both the types of strings.We also learnt to pass strings to a function using example programs.