Handling Invalid Paths

When you pass an invalid path to std::filesystem::path, several things can happen depending on how you use the path. Here's what you need to know:

Creating std::filesystem::path Objects

Creating an std::filesystem::path object with an invalid path does not throw an error. std::filesystem::path objects are just representations of paths and do not validate the path at creation:

1#include <filesystem>
2#include <iostream>
3
4int main() {
5  std::filesystem::path invalidPath{
6    R"(C:\Invalid\Path\file.txt)"};
7  std::cout << "Path: " << invalidPath.string();
8}

1Path: C:\Invalid\Path\file.txt

Using Invalid Paths

Issues arise when you use invalid paths in operations that interact with the filesystem, such as opening a file, copying, or checking existence:

1#include <filesystem>
2#include <iostream>
3
4int main() {
5  std::filesystem::path invalidPath{
6    R"(C:\Invalid\Path\file.txt)"};
7
8  if (!std::filesystem::exists(invalidPath)) {
9    std::cerr << "Path does not exist: "
10      << invalidPath.string();
11  }
12}

1Path does not exist: C:\Invalid\Path\file.txt

Exceptions and Error Handling

Many std::filesystem operations throw exceptions if they fail. For example, std::filesystem::copy_file will throw an exception if the source or destination path is invalid. You should handle these exceptions to ensure your program can recover gracefully:

1#include <filesystem>
2#include <iostream>
3
4namespace fs = std::filesystem;
5
6int main() {
7  fs::path invalidPath{
8    R"(C:\Invalid\Path\file.txt)"};
9  fs::path destination{
10    R"(C:\Valid\Path\copy.txt)"};
11
12  try {
13    fs::copy_file(invalidPath, destination);
14  } catch (const fs::filesystem_error& e) {
15    std::cerr << "Filesystem error: " << e.what();
16  }
17}

1Filesystem error: filesystem error: cannot copy file: The system cannot find the path specified.

Key Points

1. Path Representation: Creating an fs::path object with an invalid path does not throw an error.
2. Filesystem Operations: Operations like checking existence, copying, or opening files can fail if the path is invalid.
3. Exception Handling: Use try-catch blocks to handle exceptions thrown by std::filesystem operations.

Conclusion

Handling invalid paths in std::filesystem::path involves understanding that path objects themselves do not validate the path. It's during filesystem operations that you need to check for validity and handle errors appropriately to ensure robust code.