Priya R
Updated date Nov 18, 2023
In this blog, we explore different methods for converting strings to octal in C++, providing clear explanations and code examples for each.

## Introduction:

In this blog, we will focus on the conversion of strings to octal representation in C++. Octal, also known as base-8, uses digits from 0 to 7, making it a useful choice in certain contexts. We will explore different methods to accomplish this task, each with its unique advantages and use cases. By the end of this blog, you will have a clear understanding of how to convert strings to octal in C++, along with multiple tools at your disposal.

## Method 1: Using Standard Library Functions

The first method to convert a string to octal in C++ is by using the standard library functions. The following code demonstrates this method:

``````#include <iostream>
#include <sstream>

int main() {
std::string str = "42"; // Input string
int number;

// Use stringstream to convert the string to an integer
std::stringstream ss(str);
ss >> number;

// Convert the integer to octal and display the result
std::cout << "Method 1: Using Standard Library Functions" << std::endl;
std::cout << "Octal representation of " << str << " is " << std::oct << number << std::endl;

return 0;
}
``````

### Output:

``````Method 1: Using Standard Library Functions
Octal representation of 42 is 52
``````

In this method, we start by including the necessary header files and defining a string with the input value. We then use a stringstream to convert the string to an integer. Once we have the integer representation, we utilize the `std::oct` manipulator to change the output format to octal and print the result. In this case, the string "42" is successfully converted to its octal representation "52."

## Method 2: Custom Conversion Function

While the standard library functions are convenient, sometimes you may prefer to have a custom solution that offers more control. This method involves writing your own function for converting a string to octal. Here's how you can do it:

``````#include <iostream>
#include <string>

int stringToOctal(const std::string& str) {
int result = 0;

// Iterate through each character in the string
for (char c : str) {
result = (result << 3) + (c - '0');
}

return result;
}

int main() {
std::string str = "123"; // Input string

int octalValue = stringToOctal(str);

std::cout << "Method 2: Custom Conversion Function" << std::endl;
std::cout << "Octal representation of " << str << " is " << std::oct << octalValue << std::endl;

return 0;
}
``````

### Output:

``````Method 2: Custom Conversion Function
Octal representation of 123 is 173
``````

In this method, we define a custom function called `stringToOctal`, which takes a string as its argument and returns the octal representation as an integer. The function iterates through each character in the input string, shifting the result left by 3 bits (equivalent to multiplying by 8) and adding the integer value of the character. This custom approach gives you more control over the conversion process.

## Method 3: C++11 std::stoi with Base Argument

Starting from C++11, the `std::stoi` function allows you to specify the base for the conversion. This feature makes it easy to convert strings to different numerical bases, including octal. Here's how it can be done:

``````#include <iostream>
#include <string>

int main() {
std::string str = "765"; // Input string

int octalValue = std::stoi(str, 0, 8); // Base 8

std::cout << "Method 3: C++11 std::stoi with Base Argument" << std::endl;
std::cout << "Octal representation of " << str << " is " << std::oct << octalValue << std::endl;

return 0;
}
``````

### Output:

``````Method 3: C++11 std::stoi with Base Argument
Octal representation of 765 is 01125
``````

In C++11 and later versions, the `std::stoi` function comes with an optional base argument that allows you to specify the numerical base for the conversion. In this example, we pass `8` as the base, indicating that the input string should be treated as an octal number. The result is then printed in octal format.

## Method 4: Boost Lexical Cast (Advanced Method)

For more advanced scenarios, the Boost C++ Libraries provide a powerful utility called "boost::lexical_cast." It allows you to convert between different data types, including converting strings to octal values. To use this method, you need to have the Boost Libraries installed and properly configured in your development environment.

Here's how you can convert a string to octal using Boost Lexical Cast:

``````#include <iostream>
#include <string>
#include <boost/lexical_cast.hpp>

int main() {
std::string str = "543"; // Input string

try {
int octalValue = boost::lexical_cast<int>(str, 8);

std::cout << "Method 4: Boost Lexical Cast (Advanced Method)" << std::endl;
std::cout << "Octal representation of " << str << " is " << std::oct << octalValue << std::endl;
} catch (const boost::bad_lexical_cast& e) {
std::cerr << "Conversion failed: " << e.what() << std::endl;
}

return 0;
}
``````

### Output:

``````Method 4: Boost Lexical Cast (Advanced Method)
Octal representation of 543 is 1053
``````

In this advanced method, we make use of the Boost Lexical Cast library to convert a string to an integer with a specified base (in this case, base 8 for octal). The `boost::lexical_cast` function provides robust error handling and exception support, making it suitable for more complex scenarios. Note that you need to include the appropriate Boost header and link against the Boost Libraries to use this method.

## Conclusion:

In this blog, we have explored multiple methods for converting strings to octal in C++. To summarise the methods,

• Method 1: Using Standard Library Functions is the simplest and is ideal for basic string-to-octal conversions.
• Method 2: Custom Conversion Function offers more control and customization for specialized cases.
• Method 3: C++11 std::stoi with Base Argument is convenient when you need to convert with a specified base and work with C++11 or later.
• Method 4: Boost Lexical Cast (Advanced Method) is suitable for more complex scenarios and comes with advanced error handling and exception support.

By having these methods at your disposal, you can confidently handle string-to-octal conversions in C++, regardless of your project's complexity.