What is the Use of cin.ignore() Function?
The cin. ignore() function is used to ignore or clear one or more characters from the input buffer.
// Define your desired maximum number of characters const int MaxCharacters = 100; // Ignore characters until the delimiter '\n' is encountered std::cin.ignore(MaxCharacters, '\n');
Throughout this article, we’ll look at the use of cin.ignore() and see how it can remove the input buffer effectively. By the conclusion of this guide, you’ll be well-equipped to handle user input efficiently.
What is Input Buffer in Programming Language?
The input buffer, sometimes known as the input stream buffer, is a fundamental concept in programming, particularly when dealing with input operations such as reading data from standard input (keyboard) or files.
When you read input using functions like cin in C++ or input() in Python, the data is first stored in this buffer. Extra characters, like as newlines or whitespace, may linger in the buffer if you’re not cautious, creating unexpected behaviour in your programme. Functions such as cin.ignore() aid in this process by allowing you to remove or skip unnecessary characters in the buffer before reading fresh input. This assures that the data you receive is clean and clear of any remaining data.
Use of Cin.ignore Function:
The cin.ignore() method is useful for removing any unnecessary characters or newline characters from the input buffer. Now we will see the behaviour of input buffer with and without using cin.ignore.
1. With Using Cin.ignore Function
- Read the desired input using cin.
- Immediately after reading the input, use cin.ignore() to clear the input buffer. This eliminates the possibility of leftover characters interfering with following input procedures. The cin.ignore() method accepts two arguments:
a) Using numeric_limits::max()
The maximum number of characters to ignore (for maximum value, use std::numeric_limitsstd::streamsize>::max()). Using this method, we ensure that the function clears all characters in the input buffer until the given delimiter is reached.
b) Ignoring Until Newline
The terminator character until which ignoring should end (typically ‘/n’ for a newline). In this approach, we are ignoring characters until the newline character is encountered.
- After clearing the input buffer, you may proceed with your programme logic using the input you’ve collected.
The code is as followed:
int main() {
int id;
char name[20];
// Example with cin.ignore()
std::cout > id ;
// Clear the input buffer before reading the character
std::cin.ignore(std::numeric_limits::max(), '\n');
std::cin.getline(name, 20);
std::cout
This is how the output is shown:
In this example, after reading the number, cin.ignore() is used to clear the input buffer. This ensures that any residual characters, including the newline, are removed from the buffer before reading the character input. As a result, you’ll get accurate and expected character input.
2. Without Using Cin.ignore Function
In this example, if you enter the “id” followed by pressing the “Enter” key and then enter a “name”, you might notice that the “name” input seems to be skipped. This happens because the newline character from the “id” input is still in the buffer and is read as the “name” input. This occurs especially when you are using “cin.getline”.
int main() {
int id;
char name[20];
// Example without cin.ignore()
std::cout > id ;
std::cin.getline(name, 20);
std::cout
This is how the output is shown:
Some Alternatives Approaches
Here are more alternative examples to illustrate different approaches for handling the input buffer without using cin.ignore().
1. Using a ‘while‘ Loop and 'get()' Function
int main() {
int id;
char name[20];
// Read an integer
std::cout > id;
// Clear the input buffer using a while loop and get() function
while (std::cin.get() != '\n') {
continue;
}
// Read a character
std::cout > name;
std::cout
In this example, we’re using a while loop in combination with the std::cin.get() function to read and discard characters until a newline character (‘\n’) is encountered. This loop effectively clears the input buffer after reading the integer.
CautionWhile there are alternatives, such as loop-based input buffer cleaning, they may not be as efficient or as purpose-built as cin.ignore(). Choose your method depending on context and ease of use
2. Using ignore() Function Without Arguments
int main() {
int id;
char name[20];
// Read an integer
std::cout > id;
// Clear the input buffer using the ignore() function
std::cin.ignore();
// Read a character
std::cout > name;
std::cout
In this example, we’re using the ignore() function without any arguments. This function without arguments discards the next character from the input buffer, effectively clearing it. It is essential to note, however, that this method is less adaptable than using cin.ignore() with parameters.
By providing a detailed alternative approach using a loop and elaborating on its limitations, this expanded guide equips you with a deeper understanding of the advantages of cin.ignore() for effective input buffer management in C++ programs.
References
Here are some reference links related to “cin.ignore” function:
- C++ Reference Websites
cppreference.com – cin.ignore()
- C++ Reference Websites
cplusplus.com – cin.ignore()
