Difference Between Forward Slash (/) and Backslash (\) in File Path

Difference between forward slash (/) and backslash (\) in file path

/ is the path separator on Unix and Unix-like systems. Modern Windows can generally use both \ and / interchangeably for filepaths, but Microsoft has advocated for the use of \ as the path separator for decades.

This is done for historical reasons that date as far back as the 1970s, predating Windows by over a decade. In the beginning, MS-DOS (the foundation to early Windows) didn't support directories. Unix had directory support using the / character since the beginning. However, when directories were added in MS-DOS 2.0, Microsoft and IBM were already using the / character for command switches, and because of DOS's lightweight parser (descended from QDOS, designed to run on lower end hardware), they couldn't find a feasible way to use the / character without breaking compatibility with their existing applications.

So, to avoid errors about "missing a switch" or "invalid switch" when passing filepaths as arguments to commands such as these:

cd/                        <---- no switch specified
dir folder1/folder2        <---- /folder2 is not a switch for dir

it was decided that the \ character would be used instead, so you could write those commands like this

cd\
dir folder1\folder2

without error.

Later, Microsoft and IBM collaborated on an operating system unrelated to DOS called OS/2. OS/2 had the ability to use both separators, probably to attract more Unix developers. When Microsoft and IBM parted ways in 1990, Microsoft took what code they had and created Windows NT, on which all modern versions of Windows are based, carrying this separator agnosticism with it.

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As backward compatibility has been the name of the game for Microsoft from all of the major OS transitions that they've undertaken (DOS to Win16/DOS, to Win16/Win32, to Win32/WinNT), this peculiarity stuck, and it will probably exist for a while yet.

It's for this reason that this discrepancy exists. It should really have no effect on what you're doing because, like I said, the WinAPI can generally use them interchangeably. However, 3rd party applications will probably break if you pass a / when they expect a \ between directory names. If you're using Windows, stick with \. If you're using Unix or URIs (which have their foundation in Unix paths, but that's another story entirely), then use /.

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In the context of C#: It should be noted, since this is technically a C# question, that if you want to write more "portable" C# code that works on both Unix and Windows (even if C# is predominantly a Windows language), you might want to use the Path.DirectorySeparatorChar field so your code uses the preferred separator on that system, and use Path.Combine() to append paths properly.

So what IS the right direction of the path's slash (/ or \) under Windows?

A file path and a URI are different. \ is correct in a Windows file path and / is correct in a URI.

So this file path: C:\Documents\Foo translates to this URI: file:///C:/Documents/Foo

What should we use forward slash / or backslash \ in absolute path of links?

URLs use forward slashes (/) (on all platforms).

Backslashes (\) are used for local file paths on Windows. URLs are not local file paths. Not even file: scheme URLs are local file paths — they are URLs.

What is the difference between \ and \\ in file path

Windows ignores double backslashes. So while the second syntax with \ is correct and you should use that one, the first with \\ works too.

The only exception is double-backslash at the very beginning of a path that indicates a UNC path.

See Universal Naming Convention.

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Though note that in many programming languages like C, C++, Java, C#, Python, PHP, Perl, a backslash works as an escape character in string literals. As such, it needs to be escaped itself (usually with another backslash). So in these languages, you usually need to use a double backslash in the string literal to actually get a single backslash for a path. So for example in C#, the following string literal is actually interpreted as C:\Personal\MyFolder\MyFile.jpg:

var path = "C:\\Personal\\MyFolder\\MyFile.jpg";

Though there are alternative syntaxes. For example in C#, you can use the following syntax with the same result:

var path = @"C:\Personal\MyFolder\MyFile.jpg";

Why R uses forward slash (/) and not backslash (\) in file paths

Interesting question.

First off, the "forward slash" / is actually more common as it used by Unix, Linux, and macOS.

Second, the "backward slash" \ is actually somewhat painful as it is also an escape character. So whenever you want one, you need to type two in string: "C:\\TEMP".

Third, R on Windows knows this and helps! So you can you use a forward slash whereever you would use a backward slash: "C:/TEMP" works the same!

Fourth, you can have R compute the path for you and it will use use the separator: file.path("some", "dir").

So the short answer: R uses both on Windows and lets you pick whichever you find easier. But remember to use two backward slashes (unless you use the very new R 4.0.0 feature on raw strings which I'll skip for now).

Difference between forward and backslash

Well, in most languages backslashes need to be escaped in string literals, slashes do not. Further backslashes only work on Windows, while slashes work pretty much everywhere.

On the other hand, when passing path names as arguments to Windows programs, using slashes might not work because many Windows programs use slashes to signify command line flags, so you need to use backslashes.

On . vs. ..: . is the current directory, .. is the parent directory.

Difference between File.separator and slash in paths

With the Java libraries for dealing with files, you can safely use / (slash, not backslash) on all platforms. The library code handles translating things into platform-specific paths internally.

You might want to use File.separator in UI, however, because it's best to show people what will make sense in their OS, rather than what makes sense to Java.

Update: I have not been able, in five minutes of searching, to find the "you can always use a slash" behavior documented. Now, I'm sure I've seen it documented, but in the absense of finding an official reference (because my memory isn't perfect), I'd stick with using File.separator because you know that will work.

Why Path in VS C++ contains forward slash not backslash?

Windows accepts both forward- and backslash as path separator. At least since Windows XP.

I cannot read minds, but I could guess that forward slash was used in the name of (potential) portability and/or standards compliance because backslash in an include directive has undefined behaviour in c++03.

c++03 §2.8/2:

If either of the characters ’ or \, or either of the character sequences /* or // appears in a q-char-sequence or a h-char-sequence, or the character " appears in a h-char-sequence, the behavior is undefined.

The wording was changed in c++11 according to the draft. The behaviour is no longer undefined, but still implementation defined.

c++11 draft §2.9/2

The appearance of either of the characters ’ or \ or of either of the character sequences /* or // in a
q-char-sequence or an h-char-sequence is conditionally supported with implementation-defined semantics, as
is the appearance of the character " in an h-char-sequence.

About your bug:

If I change the path to #include "..\this\thread.hpp" it finds the file

Pay close attention to your two different include directives. There's more difference than the path separator. Firstly, the forward slash version doesn't refer to parent path (../), secondly the path is enclosed in < > which is wrong in this case since it appears that the path is intended to be relative to the current file. See https://stackoverflow.com/a/21594/2079303 for more details.

What is the difference between using / and \\ in specifying folder location in python?

On Unix systems, the folder separator is /, while on Windows systems, the separator is \. Unfortunately this \ is also an escape character in most programming languages and text based formats (including C, Python and many others). Strangely enough a / character is not allowed in windows paths.

So Python on windows is designed to accept both / and \ as folder separator when dealing with the filesystem, for convenience. But the \ must be escaped by another \ (unless of course you use raw strings like r'backslashes are now normal characters \\\ !')

Selenium, on the other hand, will write values into Firefox preferences, which, unlike Python, expects the appropriate kind of separator. That's why using forward slashes does not work in your example.

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