Add a FilePath object

base/file_path.h

+// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// FilePath is a container for pathnames stored in a platform's native string
+// type, providing containers for manipulation in according with the platform's
+// conventions for pathnames.  It supports the following path types:
+//
+//                   POSIX            Windows
+//                   ---------------  ----------------------------------
+// Fundamental type  char[]           wchar_t[]
+// Encoding          unspecified*     UTF-16
+// Separator         /                \, tolerant of /
+// Drive letters     no               case-insensitive A-Z followed by :
+// Alternate root    // (surprise!)   \\, for UNC paths
+//
+// * The encoding need not be specified on POSIX systems, although some
+//   POSIX-compliant systems do specify an encoding.  Mac OS X uses UTF-8.
+//   Linux does not specify an encoding, but in practice, the locale's
+//   character set may be used.
+//
+// FilePath objects are intended to be used anywhere paths are.  An application
+// may pass FilePath objects around internally, masking the underlying
+// differences between systems, only differing in implementation where
+// interfacing directly with the system.  For example, a single
+// OpenFile(const FilePath &) function may be made available, allowing all
+// callers to operate without regard to the underlying implementation.  On
+// POSIX-like platforms, OpenFile might wrap fopen, and on Windows, it might
+// wrap _wfopen_s, perhaps both by calling file_path.value().c_str().  This
+// allows each platform to pass pathnames around without requiring conversions
+// between encodings, which has an impact on performance, but more imporantly,
+// has an impact on correctness on platforms that do not have well-defined
+// encodings for pathnames.
+//
+// Several methods are available to perform common operations on a FilePath
+// object, such as determining the parent directory (DirName), isolating the
+// final path component (BaseName), and appending a relative pathname string
+// to an existing FilePath object (Append).  These methods are highly
+// recommended over attempting to split and concatenate strings directly.
+// These methods do not function as mutators but instead return distinct
+// instances of FilePath objects, and are therefore safe to use on const
+// objects.  The objects themselves are safe to share.

[darin (slow to review), 2008/10/03 16:51:50]

"share [between threads]" ?

+//
+// To aid in initialization of FilePath objects from string literals, a
+// FILE_PATH_LITERAL macro is provided, which accounts for the difference
+// between char[]-based pathnames on POSIX systems and wchar_t[]-based
+// pathnames on Windows.
+//
+// Because a FilePath object should not be instantiated at the global scope,
+// instead, use a FilePath::CharType[] and initialize it with
+// FILE_PATH_LITERAL.  At runtime, a FilePath object can be created from the
+// character array.  Example:
+//
+// | const FilePath::CharType kLogFileName[] = FILE_PATH_LITERAL("log.txt");
+// |
+// | void Function() {
+// |   FilePath log_file_path(kLogFileName);
+// |   [...]
+// | }
+
+#ifndef BASE_FILE_PATH_H_
+#define BASE_FILE_PATH_H_
+
+#include <string>
+
+#include "base/basictypes.h"
+
+// Windows-style drive letter support and pathname separator characters can be
+// enabled and disabled independently, to aid testing.  These #defines are
+// here so that the same setting can be used in both the implementation and
+// in the unit test.
+#if defined(OS_WIN)
+#define FILE_PATH_USES_DRIVE_LETTERS
+#define FILE_PATH_USES_WIN_SEPARATORS
+#endif  // OS_WIN
+
+// An abstraction to isolate users from the differences between native
+// pathnames on different platforms.
+class FilePath {
+ public:
+#if defined(OS_POSIX)
+  // On most platforms, native pathnames are char arrays, and the encoding
+  // may or may not be specified.  On Mac OS X, native pathnames are encoded
+  // in UTF-8.
+  typedef std::string StringType;
+#elif defined(OS_WIN)
+  // On Windows, for Unicode-aware applications, native pathnames are wchar_t
+  // arrays encoded in UTF-16.
+  typedef std::wstring StringType;
+#endif  // OS_WIN
+
+  typedef StringType::value_type CharType;
+
+  // Null-terminated array of separators used to separate components in
+  // hierarchical paths.  Each character in this array is a valid separator,
+  // but kSeparators[0] is treated as the canonical separator and will be used
+  // when composing pathnames.
+  static const CharType kSeparators[];
+
+  // A special path component meaning "this directory."
+  static const CharType kCurrentDirectory[];
+
+  // A special path component meaning "the parent directory."
+  static const CharType kParentDirectory[];
+
+  FilePath() {}
+  FilePath(const FilePath& that) : path_(that.path_) {}
+  explicit FilePath(const StringType& path) : path_(path) {}
+
+  FilePath& operator=(const FilePath& that) {
+    path_ = that.path_;
+    return *this;
+  }
+
+  const StringType& value() const { return path_; }
+
+  // Returns a FilePath corresponding to the directory containing the path
+  // named by this object, stripping away the file component.  If this object
+  // only contains one component, returns a FilePath identifying
+  // kCurrentDirectory.  If this object already refers to the root directory,
+  // returns a FilePath identifying the root directory.
+  FilePath DirName() const;
+
+  // Returns a FilePath corresponding to the last path component of this
+  // object, either a file or a directory.  If this object already refers to
+  // the root directory, returns a FilePath identifying the root directory;
+  // this is the only situation in which BaseName will return an absolute path.
+  FilePath BaseName() const;
+
+  // Returns a FilePath by appending a separator and the supplied path
+  // component to this object's path.  Append takes care to avoid adding
+  // excessive separators if this object's path already ends with a separator.
+  // If this object's path is kCurrentDirectory, a new FilePath corresponding
+  // only to |component| is returned.  |component| must be a relative path;
+  // it is an error to pass an absolute path.
+  FilePath Append(const StringType& component) const;
+
+  // Returns true if this FilePath contains an absolute path.  On Windows, an
+  // absolute path begins with either a drive letter specification followed by
+  // a separator character, or with two separator characters.  On POSIX
+  // platforms, an absolute path begins with a separator character.
+  bool IsAbsolute() const;
+
+ private:
+  // If this FilePath contains a drive letter specification, returns the
+  // position of the last character of the drive letter specification,
+  // otherwise returns npos.  This can only be true on Windows, when a pathname
+  // begins with a letter followed by a colon.  On other platforms, this always
+  // returns npos.
+  StringType::size_type FindDriveLetter() const;
+
+  // Remove trailing separators from this object.  If the path is absolute, it
+  // will never be stripped any more than to refer to the absolute root
+  // directory, so "////" will become "/", not "".  A leading pair of
+  // separators is never stripped, to support alternate roots.  This is used to
+  // support UNC paths on Windows.
+  void StripTrailingSeparators();
+
+  StringType path_;
+};
+
+// Macros for string literal initialization of FilePath::CharType[].
+#if defined(OS_POSIX)
+#define FILE_PATH_LITERAL(x) x
+#elif defined(OS_WIN)
+#define FILE_PATH_LITERAL(x) L ## x
+#endif  // OS_WIN
+
+#endif  // BASE_FILE_PATH_H_