std::filesystem::absolute, std::filesystem::system_complete

Defined in header `<filesystem>`
path absolute( const std::filesystem::path& p, const std::filesystem::path& base = std::filesystem::current_path() );	(1)	(since C++17)
path system_complete(const std::filesystem::path& p); path system_complete(const std::filesystem::path& p, std::error_code& ec);	(2)	(since C++17)

1) Returns absolute path of p relative to base according to the following rules:

If p has both root name and root directory (e.g. "C:\users", then the path is returned, unmodified.
If p has a root name not followed by a root directory (e.g. "C:text.txt"), then base is inserted between p's root name and the remainder of p. Formally, p.root_name() / absolute(base).root_directory() / absolute(base).relative_path() / p.relative_path() is returned,
If p has no root name, but has a root directory (e.g. "/var/tmp/file.txt" on a POSIX system or "\users\ABC\Document.doc" on Windows), then the root name of base, if it has one, is prepended to p (on a POSIX system, p is not modified, on a Windows system, "\users\ABC\Document.doc" becomes "C:\users\ABC\Document.doc". Formally, absolute(base).root_name() / p is returned.
If p has no root name and no root directory (e.g. "../file.txt", then the entire base is prepended to p. Formally, absolute(base) / p is returned.

2) Obtains the absolute path that identifies the file that the OS file opening API would access given the pathname p. On POSIX systems, this is equivalent to (1) with the default base (current_path()). On Windows systems, each logical drive has its own current working directory, and so if p is not already absolute and has a root name component (e.g. "E:filename.txt", that drive's current working directory is used, which may have been set by an earlier executed program.

Parameters

p	-	path to convert to absolute form
base	-	path (not necessarily absolute) to serve as the starting location
ec	-	out-parameter for error reporting in the non-throwing overload

Return value

Returns an absolute (although not necessarily canonical) path formed by combining p and base as described above.

Exceptions

The overload that does not take a std::error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first argument, base as the second argument, and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. The overload taking a std::error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur. This overload has

noexcept specification:

noexcept

Notes

On systems that support root names (e.g. Windows), the result of calling absolute on a relative path that has a root name (e.g. "D:file.txt" when the root name of base is different will usually result in a non-existent path.

Example

Run this code

#include <iostream>
#include <filesystem>
namespace fs = std::filesystem;
int main()
{
    fs::path p = "C:cl.exe";
    std::cout << "Current path is " << fs::current_path() << '\n'
              << "Absolute path for " << p << " is " << fs::absolute(p) << '\n'
	      << "System complete path for " << p << " is " << fs::system_complete(p) << '\n';
}

Possible output:

Current path is "D:/local/ConsoleApplication1"
Absolute path for "C:cl.exe" is "C:/local/ConsoleApplication1/cl.exe"
System complete path for "C:cl.exe" is "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\bin\cl.exe"

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

canonicalweakly_canonical (C++17)	composes a canonical path (function)
relativeproximate (C++17)	composes a relative path (function)