Check whether a path is absolute or relative

How do you check whether a path is absolute or relative, using C on L开发者_开发问答inux?

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Absolute paths tend to start with the / character. Anything else is pretty much relative from the working directory.

Even directories with .. sequences in them are considered absolute if they start with / since they end up at the same position in the file system (unless you change links and things but that's beyond the discussion of absolute and relative).

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It's absolute if it begins with a /, otherwise relative.

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Check if the path starts with / or not. if path starts with / you can assume it is absolute.

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Check if the path starts with / or not. if path starts with / you can assume it is absolute otherwise it's relative means it will update from pwd(present working directory) But in Absolute case path will update relative to root directory

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On Unix like systems (incl. Linux, macOS)

If it starts with a slash it's absolute, otherwise it's relative. That is because everything is part of a single tree starting at the root (/) and file systems are mounted somewhere in this tree.

On Windows

Windows uses backslashes (though slashes are also supported these days) and drive letters. But it's bit more complex:

• A path starting with a drive letter followed by a colon not followed by a backslash (or slash) can be relative to that drive's current directory.
• A path starting with a backslash (or slash) is absolute but on the current drive, so in that sense it is in fact relative (to the top of the current drive).
• A path starting with 2 backslashes is an UNC path (pointing to a network location) which is always absolute, except when the path starts with \\?\ which is a special case to support longer paths.

So on Windows it's best to use the PathIsRelative() (PathIsRelativeA/PathIsRelativeW) function to determine if the path is relative or not.