C++ std::string class
In the C++ programming language, std::string is a built-in C++ standard library class that provides C++ users with a popular way to store and manipulate string character text information in a continuous sequence.
Prior to C++, string data type information was typically declared and handled using the character array (char[]) format. Remember, managing and processing character array data type variables is a complex task because C++ programmers must manually manage the allocated memory, define string length, and the null string terminator (‘\0’) in the program.
The std::string class method was introduced to make handling user-defined string data types secure, easy, and more efficient in C++ programs.
std::string emp_name = “Siddhi”;
Here in this declaration, emp_name is a user-defined object of the std::string class.
Why do programmers need std::string in a C++ program?
We can understand this by declaring a fixed-size character array data type.
char comp_name[100] = “Vcanhelpsu Edtech”;
Common string class problems.
- Fixed-size declaration.
- Risk of memory buffer overflow.
- Manual memory management issues.
- Limited built-in string data operations.
With the std::string string class.
std::string comp_name = “Vcanhelpsu Edtech”;
comp_name += ” Platform”;
Here, the + add operator is used to add a new string element to comp_name.
std::string is a class in C++ programming.
In C++, a built-in string class is a user-defined data type that has the following elements by default:
- String class data member elements.
- String class member functions.
Remember, std::string is a built-in class in C++ that stores and processes characters declared in a C++ program, and provides several ready-made functions for working with the string data type.
std::string class example.
std::string comp_name = “Vcanhelpsu”;
In this example, a string variable named comp_name stores a value object.
- Character data info (Vcanhelpsu).
- Current comp_name variable length.
- Stores memory capacity information.
How string data type variables are stored internally in a C++ program.
A character string data type variable parameter passed to a C++ program by a user is stored in memory in a continuous sequential order of characters.
Example of string data type variable storage.
std::string comp_name = “Vcanhelpsu”;
Comp_name variable representation in memory.
Index location – 0 1 2 3 4 5 6 7 8 9
String data – Vcanhelpsu
As here, the Comp_name variable is stored sequentially.
comp_name[0]
comp_name[1]
comp_name[2]
comp_name[3]
comp_name[4]
Comp_name string data type variable elements can be properly managed and accessed.
The Comp_name string data type is stored and processed in a secondary storage location like an array data type.
Dynamic memory management in the string data type.
The biggest advantage of the std::string class in C++ programming is its dynamic memory allocation feature.
Dynamic string data type memory allocation.
std::string comp_name = “Vcanhelpsu”;
Here, memory can be allocated for multiple character data elements for the comp_name variable at the start.
When:
comp_name += ” Edtech”;
Add a new string element if more space is needed.
- New dynamic memory is allocated for the new string element.
- Existing string data type character elements are copied.
- New characters are added to the existing string data type.
- Existing memory for the old data type is released.
The dynamic memory allocation process is automatic in C++ programming.
C++ programmers do not need to use it manually. Dynamic memory allocation features, such as:
- new
- delete
- malloc
- free
String data type size vs. storage capacity.
In a C++ program, a user-defined string data type holds two important value elements.
String data type size.
The number of characters stored in the comp_name variable declared here. std::string comp_name = “Vcanhelpsu”;
The size of the string comp_name variable.
10
Because the comp_name string variable is defined to hold 10 characters.
comp_name.size();
Output return.
10
String data type capacity.
The number of characters reserved for the comp_name variable in the current string data type.
Example of string data type capacity.
std::string comp_name = “Vcanhelpsu”;
String data type capacity size.
10
This can be a dynamic memory allocation capacity.
20
This means that the comp_name variable character string in the current string data type can store and process up to 20 characters before memory needs to be reallocated.
comp_name.capacity();
This returns the capacity value of the currently new comp_name variable character string.
String data type variable character access.
In C++ programming, user-defined character string data type variables are stored one after another in a continuous sequence.
std::string comp_name = “Vcanhelpsu”;
Here, we can access individual string data type characters in the comp_name string data type variable.
comp_name[0] // V
comp_name[1] // c
comp_name[2] // a
comp_name[3] // n
comp_name[4] // h
comp_name[5] // e
Here, string data type variable indexing starts at 0.
Safe string data access method.
comp_name.at(4);
Unlike the array data type block [], at() checks the boundary of the string data type.
comp_name.at(100);
This throws an exception in the current string data type.
String Length Concept in String Data Type.
Here, the comp_name character variable length in the string data type means that the character declared in the current program displays the number of data type elements.
std::string programming = “Java”;
String Length output.
4
Here, the string length in the string data type is obtained using:
programming.length();
or
programming.size();
Here, both built-in functions in C++ programming provide the same string length value output.
String Concatenation Concept in String Data Type.
Here, two individual string characters declared in the string data type are concatenated. Concatenation means adding two existing string values together and displaying them.
Example of String Concatenation.
std::string comp1 = “Vcanhelpsu”;
std::string comp2 = ” Edtech”;
std::string output = comp1 + comp2;
Result.
Vcanhelpsu Edtech
Explanation of String Concatenation.
- Here, both string data types create a new string.
- In the concatenation process, the characters of both strings are copied together.
- The combined output of the concatenation of both strings is stored in it.
String Comparison Concept in String Data Type.
Here, two individual string character string element values declared in the string data type can be directly compared.
std::string language1 = “Java”;
std::string language2 = “Python”;
language1 == language2
Checks equality in both string characters.
language1 < language2
This compares both string data types in lexicographical comparison (dictionary order).
String data type comparisons are performed character by character using the ASCII/Unicode values of these variables.
Example of String Comparison.
Java < Python
As in this example, the Java string character comes before the Python character in the sequence.
Searching in Strings Concept in String Data Type.
String searching is a common operation in C++ programming, in which you can find and display a particular word or character declared in a program.
std::string info = “Vcanhelpsu”;
info.find(“helpsu”);
In this example, the info string searches one substring after another until it finds the substring it finds.
Output:
4
Because the search text “helpsu” starts at index 4.
If the search text info is not found in the string, it returns “helpsu.”
std::string::npos
is returned as output.
Substrings Concept in Substrings.
Here, individual string characters are declared in the string data type. A substring is a small string that is extracted from a larger string and displayed.
Example of Substrings.
Vcanhelpsu
Substrings extract value.
helpsu
Here, we use the Substrings extract method.
info.substr(4,5);
Meaning in the Substrings extract method.
Here, it takes input from the 5th character, starting at the index 4th position in the string.
Result of the Substrings extract method.
helpsu
Concept of transforming strings into Substrings.
C++ programming allows you to use the std::string library class to transform a string data type value.
Insert transforming strings.
Adds a new character to a string data type at a specific position.
info.insert(pos, text);
Erase Transforms strings.
Removes the desired character-value element from a string data type at a specific position.
info.erase(start, count);
Replace Transforms strings.
Replaces a portion of the desired character-value element from a string data type at a specific position.
info.replace(start, count, newText);
These operations replace string characters as needed in a user-defined string data type.
Null Terminator and the std::string Concept in strings.
In the C++ programming language, C-style strings are automatically terminated with the ‘\0’ value in the std::string user-defined string.
Example of the Null Terminator.
Vcanhelpsu \0
The std::string string class hides this complexity.
As in, when communicating with the C string character function.
str.c_str();
It provides a null-terminated character array.
Example of a Null Terminator.
std::string comp_name = “Vcanhelpsu”;
const char* p = comp_name.c_comp_name();
