PathCchCanonicalize function (pathcch.h)

Converts a path string into a canonical form.

This function differs from PathCchCanonicalizeEx in that you are restricted to a final path of length MAX_PATH.

This function differs from PathAllocCanonicalize in that the caller must declare the size of the returned string, which is stored on the stack.

This function differs from PathCanonicalize in that it accepts paths with "\", "\?" and "\?\UNC" prefixes.

Note  This function, PathCchCanonicalizeEx, or PathAllocCanonicalize should be used in place of PathCanonicalize to prevent the possibility of a buffer overrun.


  [out] PWSTR  pszPathOut,
  [in]  size_t cchPathOut,
  [in]  PCWSTR pszPathIn


[out] pszPathOut

A pointer to a buffer that, when this function returns successfully, receives the canonicalized path string.

[in] cchPathOut

The size of the buffer pointed to by pszPathOut, in characters.

[in] pszPathIn

A pointer to the original path string. If this value points to an empty string, or results in an empty string once the "." and ".." elements are removed, a single backslash is copied to the buffer pointed to by pszPathOut.

Return value

If this function succeeds, it returns S_OK. Otherwise, it returns an HRESULT code, including the following.

Return code Description
The cchPathOut value is greater than PATHCCH_MAX_CCH.
A path segment exceeds the standard path segment length limit of 256 characters.
The function could not allocate a buffer of the necessary size.


This function responds to the strings "." and ".." embedded in a path. The ".." string indicates to remove the immediately preceding path segment. The "." string indicates to skip over the next path segment. Note that the root segment of the path cannot be removed. If there are more ".." strings than there are path segments, the function returns S_OK and the buffer pointed to by pszPathOut contains a single backslash, "\".

All trailing periods are removed from the path, except when preceded by the "" wild card character. In that case, a single period is retained after the '' character, but all other trailing periods are removed.

If the resulting path is a root drive ("x:"), a backslash is appended ("x:\").

This function does not convert forward slashes (/) into back slashes (\). With untrusted input, this function by itself, cannot be used to convert paths into a form that can be compared with other paths for sub-path or identity. Callers that need that ability should convert forward to back slashes before using this function.

The following examples show the effect of these strings.

Original string Canonicalized string
C:\name_1\.\name_2\..\name_3 C:\name_1\name_3
C:\name_1\..\name_2\.\name_3 C:\name_2\name_3
C:\name_1\name_2\.\name_3\..\name_4 C:\name_1\name_2\name_4
C:\name_1\.\name_2\.\name_3\..\name_4\.. C:\name_1\name_2
C:\name_1\*... C:\name_1\*.
C:\.. C:\


Requirement Value
Minimum supported client Windows 8 [desktop apps | UWP apps]
Minimum supported server Windows Server 2012 [desktop apps | UWP apps]
Target Platform Windows
Header pathcch.h
Library Pathcch.lib

See also