A string is referred to as an array of characters. In C++, a stream/sequence of characters is stored in a char array. C++ includes the std::string class that is used to represent strings. It is one of the most fundamental datatypes in C++ and it comes with a huge set of inbuilt functions. In this article, will look at the functions of string computations.
What is std::string?
The std::string is a class in C++ since C++98. This class is the standard representation for a text string. It includes some typical string operations like find, replace, concatenate, compare etc. It is present in <string> header file.
Declaration and Initialization of String
std::string company = "GeeksforGeeks!";
Commonly Used String Functions in C++
The std::string class contains functions to provide some common string operations. The below table contains some of the most commonly used functions in C++:
|
S. No.
|
Category
|
Functions and Operators
|
Functionality
|
|
1.
|
String Length |
length() or size()
|
It will return the length of the string. |
|
2.
|
Accessing Characters |
Indexing (using array[index])
|
To access individual characters using array indexing. |
|
at()
|
Used to access a character at a specified index. |
|
3.
|
Appending and Concatenating Strings |
+ Operator
|
+ operator is used to concatenate two strings. |
|
append()
|
The append() function adds one string to the end of another. |
|
4.
|
String Comparison |
== Operator
|
You can compare strings using the == operator. |
|
compare()
|
The compare() function returns an integer value indicating the comparison result. |
|
5.
|
Substrings |
substr()
|
Use the substr() function to extract a substring from a string. |
|
6.
|
Searching |
find()
|
The find() function returns the position of the first occurrence of a substring. |
|
7.
|
Modifying Strings |
replace()
|
Use the replace() function to modify a part of the string. |
|
insert()
|
The insert() function adds a substring at a specified position. |
|
erase()
|
Use the erase() function to remove a part of the string. |
|
8.
|
Conversion |
c_str()
|
To obtain a C-style string from a std::string, you can use the c_str() function. |
Note: The above functions only works for C++ Style strings (std::string objects) not for C Style strings (array of characters).
1. String Length – length() or size()
We can find the length of the string (number of characters) using either length() or size() function of the std::string class.
Syntax
string_object.size()
or
string_object.length()
Parameters
- This function does not take any parameter.
Return Value
- This function returns the number of characters in the string object.
Example
std::string text = "geeksforGeeks";
int length = text.length();
//or
int length = text.size();
It will return the length of the string text which is 13.
2. Accessing Characters – at()
Generally, we can access the character of a string using the [] array subscript operator and indexing. But std::string also has a function named at() which can be used to access the characters of the string.
Syntax
string_object.at(index);
Parameters
- index: It represents the position of the character in the string.
Return Value
- This function returns the character present at the index.
Example
std::string str = "GEEKSFORGEEKS";
std::cout << str.at(3);
The std::cout will print K on the console as it is the character present at index 3.
3. Concatenating Strings – append() or + Operator
We can concatenate string in C++ using two methods:
1. + Operator
The + operator is overloaded in the std::string class to perform string concatenation.
Syntax
string_object1 + string_object2
Example
std::string firstName = "Geeks";
std::string lastName = "forGeeks";
std::string fullName = firstName + " " + lastName;
+ operator is used to concatenate two strings. The string fullName will be “GeeksforGeeks”.
2. append()
The append() function is another member function to concatenate two strings.
Syntax
string_object1.append(string2)
Parameters
- string2: This function takes the string to be appended as a parameter. It can be both C or C++ Style string.
Return Value
- Reference to the final string.
std::string base = "Hey! Geeks";
base.append(" Welcome to GeeksforGeeks!"); // Append a string
The append() function adds one string to the end of another.
4. String Comparison – compare() or == Operator
Just like the concatenation, we can do the string comparison using two methods:
1. == Operator
The equality operator can be used to compare the two strings as it is overloaded for this operation in the std::string class.
Syntax
string_object1 == string_object2
This will return true if both the strings are equal, otherwise returns false.
Example
std::string str1 = "apple";
std::string str2 = "banana";
if (str1 == str2) {
std::cout << "Strings are equal";
}
else {
std::cout << "Strings are not equal";
}
Here, “Strings are not equal” will be printed as the == operator will return false.
2. compare()
The compare() function is a member function of std::string class which can be used to compare two strings.
Syntax
str1.compare(str2);
Parameters
- str2: It is the string to be compared. It can be both C or C++ style string.
Return Value
- If the strings are equal, return zero.
- If str1 is greater than str2, return value >0
- If str2 is greater than str1, return value <0
Example
string str1 = "Geeks";
string str2: = "Geeksfor";
int result = str1.compare(str2);
The result will contain a value less than zero as str2 is greater than str1.
We can also compare the substring of str2 using the compare function():
str1.compare(position, length, str2);
where,
- position: position of the first character substring.
- length: length of the substring.
- str2: String object to be compared.
5. Searching – find()
We can use the find() function of the std::string class to check whether a given character or a substring is present in the string or a part of string.
Syntax of find()
str1.find(var);
Parameters
- var: It can be a C style string, C++ style string, or a character that is to be searched in the string.
Return Value
- It returns the pointer to the first occurrence of the character or a substring in the string.
Example
std::string text = "C++ Programming";
int position = text.find("Programming"); // Find the position of a substring
The position variable will contain 4 which is the start of the first occurrence of the string “Programming” in string text.
6. Generate Substring – substr()
We can use the substr() function to generate a part of the string as a new string object. It is a member function of the std::string class.
Syntax of substr() in C
str1.substr(start, end);
Parameters
- start: Starting position of the substring to be generated.
- end: Ending of the substring to be generated.
Return Type
- It returns the newly created string object.
Example
std::string text = "Hello, World!";
std::string sub = text.substr(7, 5); // Extract "World"
In the above example. the sub string will contain the “World”.
Modifying Strings
The following function allows us to modify the current string.
1. insert()
The insert() function not only allows us to add a string but also allows us to add it at the specified position. It is also a member function of the std::string class.
Syntax
str1.insert(index, str2);
Parameters
- str2: string to be inserted.
- index: position of where to insert the new string
Return Type
Example
std::string text = "I have a cat.";
text.insert(9, " black"); // Insert " black" at position 9
2. replace()
The replace() function replaces the part of the string with the given other string. Unlike insert, the characters in the part where the new string is to be inserted are removed.
Syntax
str1.replace(index, size, str2);
Parameters
- index: Index of where to start replacing the new string.
- size: length of the part of the string that is to be replaced.
- str2: new string that is to be inserted.
Return Type
Example
std::string text = "I like dogs.";
text.replace(7, 4, "cats"); // Replace "dogs" with "cats"
3. erase()
The erase() function is a member function of std::string class that is used to remove a character or a part of the string.
Syntax
str1.erase(start, end);
Parameters
- start: Starting position.
- end: Ending position.
Return Type
Example
std::string text = "This is an example.";
text.erase(5, 3); // Erase "is "
Convert std::string to C String – c_str)_
The c_str() function is a member function that is used to convert the C++ style string i.e. std::string objects to C style string i.e. array of characters.
Syntax
str1.c_str()
Parameters
- This function does not take any parameter.
Return Value
- Pointer to the equivalent array of characters.
Example
std::string str = "C++";
const char* cstr = str.c_str()
Example of String Functions in C++
The below code demonstrate the use of the above specified string functions:
C++
#include <iostream>
#include <string>
using namespace std;
int main()
{
string greeting = "Hello, World!";
cout << greeting << endl;
string name;
cout << "Enter your name: ";
cin >> name;
cout << name << endl;
int length = greeting.length();
cout << length << endl;
char firstChar = greeting[0];
char secondChar = greeting.at(1);
cout << firstChar << " " << secondChar << endl;
string firstName = "Geek";
string lastName = "Geeks";
string fullName = firstName + " " + lastName;
cout << fullName << endl;
string base = "Hello";
cout << base << endl;
base.append(" World!");
cout << base << endl;
string str1 = "apple";
string str2 = "banana";
if (str1 == str2) {
cout << "Strings are equal" << endl;
}
else {
cout << "Strings are not equal" << endl;
}
int result = str1.compare(str2);
if (result == 0) {
cout << "Strings are equal" << endl;
}
else if (result < 0) {
cout << "str1 comes before str2" << endl;
}
else {
cout << "str1 comes after str2" << endl;
}
string text = "Hello, World!";
cout << text << endl;
string sub = text.substr(7, 5);
cout << sub << endl;
string searchIn = "C++ Programming";
size_t position = searchIn.find("Programming");
if (position != string::npos) {
cout << "Found at position " << position << endl;
}
else {
cout << "Not found" << endl;
}
string modify = "I like dogs.";
modify.replace(7, 4, "cats");
cout << modify << endl;
modify.insert(6, " black");
cout << modify << endl;
modify.erase(6, 6);
cout << modify << endl;
string str = "C++";
const char* cstr = str.c_str();
cout << cstr << endl;
return 0;
}
|
Output
Hello, World!
Enter your name: Geeks
Geeks
13
H e
Geek Geeks
Hello
Hello World!
Strings are not equal
str1 comes before str2
Hello, World!
World
Found at position 4
I like cats.
I like black cats.
I like cats.
C++
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