std文件流的相对路径

Question

Is it possible to provide a root folder and after this only relative paths for std::ifstream and std::ofstream?

For example:

SetFileStreamRootFolder("C:/");
std::ifstream stream("isample.txt"); //C:\isample.txt file
std::ofstream stream("osample.txt"); //C:\osample.txt file

Answer 1

You can define your own method which knows the working directory and prepends the correct string to the filename.

std::string prependFilePath(const std::string &filename);

Then construct a stream with

stream(prependFilePath("isample.txt").c_str());

---

Example:

std::string prependFilePath(const std::string &filename)
{
    // The path can be relative or absolute
    return "../" + filename;
}

In a real implementation, you should store the path (eg: ../ ) in a const std::string member rather than hard-coding it and probably this method is a good candidate for getting a static modifier (real helper/utility method).

Answer 2

If you write a function, yes.
The fstream -objects do not impose anything on you, you can specify a relative path or an absolute path.

Cplusplus.com states:

Parameters:
filename

String with the name of the file to open.
Specifics about its format and validity 
depend on the library implementation and running environment.

Answer 3

Sure, using Boost.Filesystem

#include <boost/filesystem.hpp>
...
namespace fs = boost::filesystem;
fs::current_path("C:/");

Filesystem, or something like it, is slated for inclusion in the standard library. VS2012 includes a preliminary implementation of it. So if you don't have Boost, and you don't feel like installing it, you can use that.

#include <filesystem>
...
namespace fs = std::tr2::sys;
fs::current_path(fs::path("C:/"));