Relative Paths Between Absolute Paths

To find the relative path between two absolute paths in C++, you can use the std::filesystem::relative() function.

This function computes the relative path from one absolute path to another. Here’s how you can do it:

1#include <filesystem>
2#include <iostream>
3
4int main() {
5  std::filesystem::path base{
6    R"(C:\Users\example\projects)"};
7  std::filesystem::path target{
8    R"(C:\Users\example\projects\subdir\file.txt)"};
9
10  std::filesystem::path relativePath =
11    std::filesystem::relative(target, base);
12  std::cout << "Relative Path: "
13    << relativePath.string();
14}

1Relative Path: subdir\file.txt

Key Points

1. Base Path: The starting point from which you want to calculate the relative path.
2. Target Path: The destination path you want to reach relative to the base path.
3. Function: Use std::filesystem::relative(target, base) to compute the relative path.

Understanding Relative Paths

Relative paths are crucial when you want to specify paths relative to a certain directory, especially in projects that may be moved between different environments. This makes your code more flexible and portable.

Handling Different Platforms

std::filesystem::relative() handles platform-specific path separators, making it a robust solution for cross-platform applications. Whether you’re working on Windows with backslashes (\) or on Unix-like systems with forward slashes (/), the function ensures the correct path format.

Error Handling

Ensure both paths are absolute. If you pass relative paths to std::filesystem::relative(), it will throw an error. Here’s how to handle it:

1#include <filesystem>
2#include <iostream>
3
4namespace fs = std::filesystem;
5
6int main() {
7  fs::path base{
8    R"(C:\Users\example\projects)"};
9  fs::path target{
10    R"(C:\Users\example\projects\subdir\file.txt)"};
11
12  try {
13    fs::path relativePath =
14      fs::relative(target, base);
15    std::cout << "Relative Path: "
16      << relativePath.string();
17  } catch (const fs::filesystem_error& e) {
18    std::cerr << "Error: " << e.what();
19  }
20}

1Relative Path: subdir\file.txt

Conclusion

Finding the relative path between two absolute paths using std::filesystem::relative() is straightforward and ensures your paths remain flexible and portable. Always handle exceptions to manage any potential errors gracefully.