String To Int C++ : Top 6 Conversion Methods

C++

In the realm of programming, data type conversions are commonplace. Among these, the transformation of a string to an integer (int) in C++ holds notable significance. This conversion is pivotal as it allows the manipulation and utilization of numeric data that initially exists in string format, which is often the case when dealing with user input or reading from files.

C++ provides a variety of methods to achieve this conversion, encompassing functions like stoi or atoi, and stream classes. Each method comes with its own set of advantages, catering to different scenarios and requirements. Through this guide, we’ll delve into various techniques of converting a string to an integer in C++, aiding you in choosing the most suitable method for your programming endeavors.

The following are the 6 functions that can be leveraged to achieve string to integer conversion

Convert String To Int C++

Convert string to int is very simple, Here we discussed the 6 ways to convert. Just click the links below to reach direct to the method section or check all the way to explore the best possible methods.

1. string streams,
2. std::atoi
3. std::stoi
4. boost::lexical_cast
5. sscanf
6. for loop with Range

string streams

The first and also I love this way to convert string to int C++.

To convert from string representation to integer value, we can use std::stringstream.

if the value converted is out of range for the integer data type, it returns INT_MIN or INT_MAX.

Also if the string value can’t be represented as a valid int data type, then 0 is returned.

#include 
#include 
#include 

int main() {
	
	std::string x = "50";
	int y;
	std::istringstream(x) >> y;
	std::cout << y << '\n';
	return 0;
}

Output:
50

As per the above output, we can see it converted from string numbers to an integer numbers.

std::atoi

This comes in our 2nd list to learn how to convert string to int c++,

Lets use std::atoi function to convert a string variable to an int value.

This function takes c string as argument or parameter.

For this, we need to parse the input string to a c string, which can be done using std::string::c_str.

Here std::string::c_str will help as the parse method.

Finally, the converted value will be passed to std:atoi function.

#include 
#include 
#include 

int main() {

	std::string x = "50";
	int y = std::atoi(x.c_str());
	std::cout << y << '\n';
	return 0;
}

Output:
50

Also, Check,

std::stoi

Int C++

3rd and most powerful way to convert string to int c++,

For converting a string to an integer numeric type, the traditional approach is to use std::stoi function.

stoi was part of the C++11 version.

Passing valid integers will provide the right input.

In case of invalid or bad input, this function throws integer overflow or std::out_of_range or std::invalid_argument exception.

#include 
#include 

int main() {

	std::string x = "50";
	try
	{
		int y = std::stoi(x);
		std::cout << y << '\n';
	}
	catch (std::invalid_argument const &ex)
	{
		std::cout << "Invalid input" << '\n';
	}
	catch (std::out_of_range const &ex)
	{
		std::cout << "Integer overflow" << '\n';
	}
	return 0;
}

Output:
50

boost::lexical_cast

boost::lexical_cast is our 4th way to convert string to int c++.

We can also use boost::lexical_cast to convert string to an integer.

In case of any issue, it throws boost::bad_lexical_cast exception.

#include <boost/lexical_cast.hpp>
#include 
#include 

int main() {
 
	std::string x = "50";
	int y;

	try {
		y = boost::lexical_cast(x);
		std::cout << y << '\n';
	}
	catch (boost::bad_lexical_cast const &ex)
	{
		std::cout << "error" << '\n'; } return 0; }  b>Output:
50

sscanf

Coming to 5th method “sscanf” is one more method to convert it.

We can leverage scanf function to convert string to an integer type.

This function accepts c string as a parameter.

#include 
#include 
#include 

int main() {
	
	std::string x = "50";
	int y;

	if (sscanf(x.c_str(), "%d", &y) == 1) {
		std::cout << y << '\n';
	} else {
		std::cout << "Invalid Input";
	}

	return 0;
}

Output:
50

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for loop with Range

This is our last way to convert string to int C++.

We can write custom for loop function to convert string to an integer numeric value.

The aim is to loop the characters of string using range-based for loop.

This function accepts c string as a parameter.

#include 
#include 

int main()
{
	std::string x = "50";
	int y = 0;
	for (char c: x)
	{
		if (c >= '0' && c <= '9') {
			y = y * 10 + (c - '0');
		}
		else {
			std::cout << "Invalid Input";
			return 1;
		}
	}
	std::cout << y << '\n';
	return 0;
}

Output:
50

Also, we can use printf to print the format specifier like float, integer, character, string, octal, and hexadecimal.

Note: if you pass floating-point values i.e passing decimal value as a decimal string, then the final result will still be an integer(decimal rounded off to integer).

To conclude this tutorial, we covered various types of implementation to achieve string to int c++ conversion.

Frequently Asked Questions