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.
- string streams,
- std::atoi
- std::stoi
- boost::lexical_cast
- sscanf
- 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,
Convert List To String In Javastd::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
You may like,
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
How can I convert a std::string to int in C++?
There are several methods to convert a string to an integer in C++ such as using `std::stringstream`, `std::stoi`, or `atoi`. The `std::stringstream` method is useful but 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.
Are there any case sensitivity issues when converting a string to int in C++?
Yes, case sensitivity matters in C++. For instance, if you declare your string as ‘s’, you need to use ‘s’, not ‘S’ when calling it. Also, remember to properly end your instruction with a semicolon.
What libraries can be used for parsing a string to an int in C++?
Boost.Spirit.Karma library is known to be fast for converting integers to strings, and by extension can be used for parsing strings to integers. Another safer method for string to integer conversion is using `strtol()` function.
How can I handle preceding zeros when converting a string to int in C++?
When using `std::istringstream` to convert a string to an integer, you may use the `dec` modifier to handle any preceding zeros. For example: `text_stream >> dec >> value;`.
Is there a specific way to convert string to int inside a loop in C++?
Yes, when converting a string to int inside a loop, it’s advisable to place the conversion code such as `int num = atoi(testing);` outside the loop to avoid unnecessary repetitions and potential errors during each iteration.
What are some common methods to convert string to int in C++?
Common methods include using `std::stoi` function, `atoi` function, `std::stringstream`, and `std::istringstream`. The `std::stoi` function is considered to be a modern and easy way to perform this conversion.
What are the modern C++-style ways to convert string to int?
The modern C++-style way to convert string to int is by using the `std::stoi()` function which is introduced in C++11. This function provides a straightforward way to perform the conversion.
Is there a way to manually convert a string to int in C++?
Yes, you can manually convert a string to int by iterating through the string, checking for digits, extracting all digits, and then handling any leading ‘-‘ sign to determine if the integer should be negative or positive. However, this method can be more complicated and prone to errors compared to using built-in functions or libraries.