C++ input validation


In C++ programming, strong input validation is important for writing reliable and secure software. Validating user input is an important part of input validation. It meets the specified criteria, preventing unexpected behavior and potential security vulnerabilities. Input must be validated before any processing or operations are performed. This is important because incorrect input that is not handled properly can cause the system to crash.

C++ has some nice techniques for validating most types of input. This article explores the importance of input validation in C++, ways to achieve it, and best practices for increasing the overall integrity of user input.

What is input validation in C++?

Think of your program as a complex machine. Just as a machine needs the right fuel to function properly, your program needs accurate data to produce the right results. Input validation acts as a gatekeeper, ensuring that only valid information enters your program, preventing it from breaking due to bad data. C++ provides helper tools that issue alerts when errors are encountered in the input.

Importance of input validation

Input validation serves many purposes in C++ programming and some of them are listed in the following:

    • Preventing invalid data: This ensures that data entered by users follows the expected format and type, reducing the possibility of runtime errors.
    • Enhancing Security: It protects against malicious input, such as SQL injection or buffer overflow attacks, by validating and sanitizing user-supplied data.
    • User Experience Improvements: It provides informative feedback to users, guiding them to enter correct and valid data, thereby increasing the overall usability of the software.
    • Avoiding Undefined Behavior: This helps prevent undefined behavior caused by invalid data that may lead to crashes or unexpected program states.

Now, let's move on to examples to learn how to validate input in a C++ program. The examples given will help us improve our understanding of this important technology and allow us to find practical approaches to incorporating it into C++ programs.

Scenario 1: Ensuring Accuracy (Validating Integer Input in C++)

Imagine that your program only needs to work with precise numbers such as integers. To achieve this, we can use the built-in functionality of “sin” to assess the validity of the input. This allows us to ensure that only valid integers are accepted and processed by the program, eliminating any unwanted data.

Here is a program that demonstrates how to validate integer input in a C++ program:

using namespace std;
int main,,,
you inpt;
court,“Enter integer= “,
cin.ignore,numerical limits<stream size,::Maximum,,, '\n',,
court,“Wrong Input”,Andal;
court,“Enter valid input=”,
to break,
court,finally,“integer is=”,input,Andal;
return 0,

When you execute the previous program, it will ask you to enter an integer. After taking input from the user, the program enters a “while” loop that continues until the user enters a valid integer. When a user inputs something incorrectly, the code clears the input buffer and prompts the user to enter the number again. Once the user enters a valid integer, the code will exit the “while” loop and print the integer.

Cin.fail() Checks whether the stream “cin” has entered the failed state. This happens when an error occurs during user input such as entering invalid data or exceeding the input buffer size. If no input failure has occurred the compiler moves to the following statement. “numeric_limits::max()” tells the “ignore” function to ignore the maximum possible number of characters. If the input is not a valid integer, an “Incorrect input” error will be displayed, and the user will be prompted to enter a valid integer. This continues until the compiler finds a valid integer.

The program uses this method to check user input to ensure that it only accepts integers. The output of this program is given in the following to show the response of the program to different types of inputs:

Upon executing the code, we can see how the given code performs user input validation to ensure that only integers are accepted. It performs error checking to handle invalid input and prompts the user to enter a valid number until they receive it.

Scenario 2: Validating User Input with the Power of Regular Expressions in C++

Imagine building a program that relies on precise user input such as a phone number. In C++, the user can harness the power of regular expressions to ensure that only valid information enters the program. Regular expressions allow users to define specific patterns that represent valid input. You can easily identify and reject any invalid entries by comparing the user's input against defined patterns.

By incorporating regular expressions into your C++ programs for user input validation, you can build more robust and reliable applications that process accurate data and produce optimal results. Let's look at an example of a regular expression in the following:

#Involved <स्ट्रिंग>
using namespace std;
bool valid_input,string Instring valid_chrs, ,
return all of,in.start,,At the end,,, [&valid_chrs],four chr, ,
return search,valid_chrs.start,,valid_chrs.end,,chr, ,= valid_chrs.end,,,
int main,, ,
string inp;
string valid_chrs = “abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ -“,
court , “Enter valid input (characters “)” << valid_chrs << ",,
get line,cine, inp,,
If ,valid_input,inp, valid_chrs,, ,
court , “The given input is valid!” , Andal;
, Other ,
court , “Invalid Input!” , Andal;
return 0,

<एल्गोरिदम> The header contains functions for working with sequences of elements such as “all_of” which are used later. The library includes functions to check character types. <स्ट्रिंग>The :header contains functions for working with strings such as getLine() and start()/end() iterators. The header contains functions for input/output operations such as “cout” and “sin”.

Valid_Input() function is defined. It takes two arguments: “in” which is a string containing the user's input and “valid_chrs” which is a string containing the valid characters allowed in the input. When a function is run, a Boolean value is returned that indicates whether the input string contains only characters from “valid_chrs”.

When you execute this code in your Dev++ program you will be asked to enter inputs. Once you provide the input, the program will check its validity. If the input is valid, it will pass. Otherwise, the program will give the error of invalid input. Now, let's see the output of the program in the following:

Scenario 3: Regular expressions for pattern matching

Now, let's explore the usefulness of regular expressions for pattern matching. The following example demonstrates how regular expressions help validate input, search strings, and sanitize information efficiently. Key regular expression concepts and their application in C++ scenarios helps programmers write a cleaner and more effective code. As a result, developers can expect to write programs with increased data processing capabilities and improved input reliability. Let's move on to the following code snippet:

using namespace std;
int main,,,
String inEmail;
court,“Enter your email= “,
Sin,In email;
regex email format,R,[a-zA-Z0-9._%+-],[a-zA-Z0-9.-],[a-zA-Z]{2,})”,,
If,,regex_match,In email, email format,,,
court,“invalid email!”,Andal;
return 1,
return 0,

Upon executing this program you will be asked to provide your email address. Generally, email addresses have a specific pattern that essentially includes “@”, which is valid criteria for email addresses. Once you provide the input, this program validates the input with regex_match() and either accepts the input if it is valid as per the criteria or rejects the input if it does not meet the given criteria. Is. Now, let's take a look at the output of this following program:

As you can clearly see, “swfeweg” is not a valid email address. So, the program displays “Invalid email!” Returns. Mistake. Now, let's provide the correct email address and see how the program responds:

It is clearly visible that the provided email has been accepted as it meets the criteria for the given email address. This example shows how to validate an email address using regular expressions. Depending on particular validation requirements, you can modify the regex pattern.


C++ input validation is an integral part of writing reliable and secure programs. By implementing strong input validation techniques and following best practices, developers can increase the overall integrity of their software, prevent unexpected errors, and provide a more user-friendly experience. Whether validating simple numerical inputs or complex data formats, a thoughtful and systematic approach to input validation contributes to the overall reliability and security of C++ applications.

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By Ranjan