In today’s digital world, URLs play a crucial role in connecting web resources. However, sometimes URLs may contain special characters that need to be properly encoded to ensure their correct transmission and interpretation. This is where URL encoding comes into play.

URL encoding is the process of converting special characters into a format that can be safely transmitted over the internet. In this tutorial, we will explore how to URL encode a string in C++, so let’s get started!

Understanding URL Encoding

Before diving into the code, it’s important to understand the concept of URL encoding. In a URL, certain characters have special meanings and cannot be used as-is. For example, spaces are represented as %20, and the plus sign (+) is used to represent spaces in query strings. Additionally, characters outside the ASCII range need to be encoded using a special format.

URL encoding follows a simple principle: replace each character that needs encoding with its corresponding ASCII value in hexadecimal, preceded by a percent sign (%). The encoded string can then be safely used in a URL without any conflicts or misinterpretations.

URL Encoding in C++

To URL encode a string in C++, we can make use of the <cctype> and <iomanip> libraries. The <cctype> library provides functions to check the properties of individual characters, and the <iomanip> library allows us to manipulate output streams for URL encoding purposes.

Here’s an example code snippet that demonstrates how to URL encode a string:

#include <iostream>
#include <cctype>
#include <iomanip>

std::string urlEncode(const std::string& str) {
    std::ostringstream encodedStream;
    encodedStream << std::hex << std::uppercase << std::setfill('0');

    for (char c : str) {
        if (std::isalnum(c) || c == '-' || c == '_' || c == '.' || c == '~') {
            encodedStream << c;
        } else {
            encodedStream << '%' << std::setw(2) << static_cast<unsigned int>(static_cast<unsigned char>(c));

    return encodedStream.str();

int main() {
    std::string originalString = ""Hello World!"";
    std::string encodedString = urlEncode(originalString);

    std::cout << ""Original string: "" << originalString << std::endl;
    std::cout << ""Encoded string: "" << encodedString << std::endl;

    return 0;

In this code snippet, we define the urlEncode function that takes a std::string parameter and returns the URL encoded string. The function iterates through each character of the input string and checks if it is alphanumeric or belongs to a set of allowed characters (-, _, ., ~). If the character needs encoding, it is converted to its hexadecimal ASCII value using std::setw and printed to the encodedStream. Otherwise, the character is added as-is to the stream.

In the main function, we provide an example usage of the urlEncode function. We encode the string ““Hello World!”” and output both the original and encoded strings to the console.


In this tutorial, we’ve learned how to URL encode a string in C++. URL encoding is crucial for handling special characters in URLs and ensuring their correct transmission and interpretation. By following the principles of URL encoding and implementing a simple function, we can easily encode strings in C++. I hope you found this tutorial helpful!

Feel free to explore further on URL encoding and adapt the code according to your specific needs. Happy encoding!