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diff --git a/libs/filesystem/doc/portability_guide.htm b/libs/filesystem/doc/portability_guide.htm new file mode 100644 index 0000000000..54b5a748cb --- /dev/null +++ b/libs/filesystem/doc/portability_guide.htm @@ -0,0 +1,241 @@ +<html> + +<head> +<meta http-equiv="Content-Language" content="en-us"> +<meta name="GENERATOR" content="Microsoft FrontPage 5.0"> +<meta name="ProgId" content="FrontPage.Editor.Document"> +<meta http-equiv="Content-Type" content="text/html; charset=windows-1252"> +<title>Portability Guide</title> +<link rel="stylesheet" type="text/css" href="../../../doc/src/minimal.css"> +</head> + +<body bgcolor="#FFFFFF"> + +<h1> +<img border="0" src="../../../boost.png" align="center" width="300" height="86">Path +Name Portability +Guide</h1> + +<table border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF" width="100%"> + <tr> + <td><a href="index.htm">Filesystem Home</a> + <a href="release_history.html">Releases</a> + <a href="reference.html">Reference</a> + <a href="tutorial.html">Tutorial</a> + <a href="faq.htm">FAQ</a> + <a href="portability_guide.htm">Portability</a> + <a href="v3.html">V3 Intro</a> + <a href="v3_design.html">V3 Design</a> + <a href="deprecated.html">Deprecated</a> + </td> + </tr> +</table> + +<p> +<a href="#Introduction">Introduction</a><br> +<a href="#name_check_functions">name_check functions</a><br> +<a href="#recommendations">File and directory name recommendations</a></p> +<h2><a name="Introduction">Introduction</a></h2> +<p>Like any other C++ program which performs I/O operations, there is no +guarantee that a program using Boost.Filesystem will be portable between +operating systems. Critical aspects of I/O such as how the operating system +interprets paths are unspecified by the C and C++ Standards.</p> +<p>It is not possible to know if a file or directory name will be +valid (and thus portable) for an unknown operating system. There is always the possibility that an operating system could use +names which are unusual (numbers less than 4096, for example) or very +limited in size (maximum of six character names, for example). In other words, +portability is never absolute; it is always relative to specific operating +systems or +file systems.</p> +<p>It is possible, however, to know in advance if a directory or file name is likely to be valid for a particular +operating system. It is also possible to construct names which are +likely to be portable to a large number of modern and legacy operating systems.</p> + +<p>Almost all modern operating systems support multiple file systems. At the +minimum, they support a native file system plus a CD-ROM file system (Generally +ISO-9669, often with Juliet extensions).</p> + +<p>Each file system +may have its own naming rules. For example, modern versions of Windows support NTFS, FAT, FAT32, and ISO-9660 file systems, among others, and the naming rules +for those file systems differ. Each file system may also have +differing rules for overall path validity, such as a maximum length or number of +sub-directories. Some legacy systems have different rules for directory names +versus regular file names.</p> + +<p>As a result, Boost.Filesystem's <i>name_check</i> functions +cannot guarantee directory and file name portability. Rather, they are intended to +give the programmer a "fighting chance" to achieve portability by early +detection of common naming problems.</p> + +<h2><a name="name_check_functions">name_check functions</a></h2> + +<p>A <i>name_check</i> function +returns true if its argument is valid as a directory and regular file name for a +particular operating or file system. A number of these functions are provided.</p> + +<p>The <a href="#portable_name">portable_name</a> function is of particular +interest because it has been carefully designed to provide wide +portability yet not overly restrict expressiveness.</p> + +<table border="1" cellpadding="5" cellspacing="0"> + <tr> + <td align="center" colspan="2"><b>Library Supplied name_check Functions</b></td> + </tr> + <tr> + <td align="center"><b>Function</b></td> + <td align="center"><b>Description</b></td> + </tr> + <tr> + <td align="left" valign="top"><code><a name="portable_posix_name">portable_posix_name</a>(const + std::string&<i> name</i>)</code></td> + <td><b>Returns:</b> <i>true</i> if <code>!name.empty() && name</code> contains only the characters + specified in<i> Portable Filename Character Set</i> rules as defined in by + POSIX (<a href="http://www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap03.html">www.opengroup.org/onlinepubs/007904975/basedefs/xbd_chap03.html</a>).<br> + The allowed characters are <code>0-9</code>, <code>a-z</code>, <code>A-Z</code>, + <code>'.'</code>, <code>'_'</code>, and <code>'-'</code>.<p><b>Use:</b> + applications which must be portable to any POSIX system.</td> + </tr> + <tr> + <td align="left" valign="top"><code><a name="windows_name">windows_name</a>(const + std::string&<i> name</i>)</code></td> + <td><b>Returns:</b> <i>true</i> if <code>!name.empty() && name</code> contains + only the characters specified by the Windows platform SDK as valid + regardless of the file system <code>&& (name</code> is <code>"."</code> or + <code>".."</code> or does not end with a trailing space or period<code>)</code>. + The allowed characters are anything except <code>0x0-0x1F</code>, <code>'<'</code>, + <code>'>'</code>, <code>':'</code>, <code>'"'</code>, <code>'/'</code>, + <code>'\'</code>, and <code>'|'</code>.<p> + <b>Use:</b> applications which must be portable to Windows.</p> + <p><b>Note:</b> Reserved device names are not valid as file names, but are + not being detected because they are still valid as a path. Specifically, + CON, PRN, AUX, CLOCK$, NUL, COM[1-9], LPT[1-9], and these names followed by + an extension (for example, NUL.tx7).</td> + </tr> + <tr> + <td align="left" valign="top"><code><a name="portable_name">portable_name</a>(const + std::string&<i> name</i>)</code></td> + <td><b>Returns:</b> <code> windows_name(name) && portable_posix_name(name) + && (name</code> is <code>"."</code> or <code>".."</code>, and the first character not a period or hyphen<code>)</code>.<p><b>Use:</b> applications which must be portable to a wide variety of + modern operating systems, large and small, and to some legacy O/S's. The + first character not a period or hyphen restriction is a requirement of + several older operating systems.</td> + </tr> + <tr> + <td align="left" valign="top"><code><a name="portable_directory_name"> + portable_directory_name</a>(const std::string&<i> name</i>)</code></td> + <td><b>Returns:</b> <code>portable_name(name) && (name</code> is <code>"."</code> + or <code>".."</code> or contains no periods<code>)</code>.<p><b>Use:</b> applications + which must be portable to a wide variety of platforms, including OpenVMS.</td> + </tr> + <tr> + <td align="left" valign="top"><code><a name="portable_file_name"> + portable_file_name</a>(const std::string&<i> name</i>)</code></td> + <td><b>Returns:</b> <code>portable_name(name) && </code>any period is followed by one to three additional + non-period characters.<p><b>Use:</b> + applications which must be portable to a wide variety of platforms, + including OpenVMS and other systems which have a concept of "file extension" + but limit its length.</td> + </tr> + <tr> + <td align="left" valign="top"><code><a name="native">native</a>(const + std::string&<i> name</i>)</code></td> + <td><b>Returns:</b> Implementation defined. Returns <i> + true</i> for names considered valid by the operating system's native file + systems.<p><b>Note:</b> May return <i>true</i> for some names not considered valid + by the operating system under all conditions (particularly on operating systems which support + multiple file systems.)</td> + </tr> +</table> + +<h2>File and directory name <a name="recommendations">recommendations</a></h2> + +<table border="1" cellpadding="5" cellspacing="0"> + + <tr> + <td align="center" valign="top"><strong>Recommendation</strong></td> + <td align="center" valign="top"><strong>Rationale</strong></td> + </tr> + <tr> + <td valign="top">Limit file and directory names to the characters A-Z, a-z, 0-9, period, hyphen, and + underscore.<p>Use any of the "portable_" <a href="#name_check_functions"> + name check functions</a> to enforce this recommendation.</td> + <td valign="top">These are the characters specified by the POSIX standard for portable directory and + file names, and are also valid for Windows, Mac, and many other modern file systems.</td> + </tr> + <tr> + <td valign="top">Do not use a period or hyphen as the first + character of a name. Do not use period as the last character of a name.<p> + Use <a href="#portable_name">portable_name</a>, + <a href="#portable_directory_name">portable_directory_name</a>, or + <a href="#portable_file_name">portable_file_name</a> to enforce this + recommendation.</td> + <td valign="top">Some operating systems treat have special rules for the + first character of names. POSIX, for example. Windows does not permit period + as the last character.</td> + </tr> + <tr> + <td valign="top">Do not use periods in directory names.<p>Use + <a href="#portable_directory_name">portable_directory_name</a> to enforce + this recommendation.</td> + <td valign="top">Requirement for ISO-9660 without Juliet extensions, OpenVMS filesystem, and other legacy systems.</td> + </tr> + <tr> + <td valign="top">Do not use more that one period in a file name, and limit + the portion after the period to three characters.<p>Use + <a href="#portable_file_name">portable_file_name</a> to enforce this + recommendation.</td> + <td valign="top">Requirement for ISO-9660 level 1, OpenVMS filesystem, and + other legacy systems. </td> + </tr> + <tr> + <td valign="top">Do not assume names are case sensitive. For example, do not expected a directory to be + able to hold separate elements named "Foo" and "foo". </td> + <td valign="top">Some file systems are case insensitive. For example, Windows + NTFS is case preserving in the way it stores names, but case insensitive in + searching for names (unless running under the POSIX sub-system, it which + case it does case sensitive searches). </td> + </tr> + <tr> + <td valign="top">Do not assume names are case insensitive. For example, do not expect a file + created with the name of "Foo" to be opened successfully with the name of "foo".</td> + <td valign="top">Some file systems are case sensitive. For example, POSIX.</td> + </tr> + <tr> + <td valign="top">Don't use hyphens in names.</td> + <td valign="top">ISO-9660 level 1, and possibly some legacy systems, do not permit + hyphens.</td> + </tr> + <tr> + <td valign="top">Limit the length of the string returned by path::string() to + 255 characters. + Note that ISO 9660 has an explicit directory tree depth limit of 8, although + this depth limit is removed by the Juliet extensions.</td> + <td valign="top">Some operating systems place limits on the total path length. For example, + Windows 2000 limits paths to 260 characters total length.</td> + </tr> + <tr> + <td valign="top">Limit the length of any one name in a path. Pick the specific limit according to + the operating systems and or file systems you wish portability to:<br> + Not a concern:: POSIX, Windows, MAC OS X.<br> + 31 characters: Classic Mac OS<br> + 8 characters + period + 3 characters: ISO 9660 level 1<br> + 32 characters: ISO 9660 level 2 and 3<br> + 128 characters (64 if Unicode): ISO 9660 with Juliet extensions</td> + <td valign="top">Limiting name length can markedly reduce the expressiveness of file names, yet placing + only very high limits on lengths inhibits widest portability.</td> + </tr> +</table> + +<hr> +<p>Revised +<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->20 March, 2012<!--webbot bot="Timestamp" endspan i-checksum="28814" --></p> + +<p>© Copyright Beman Dawes, 2002, 2003</p> +<p> Use, modification, and distribution are subject to the Boost Software +License, Version 1.0. (See accompanying file <a href="../../../LICENSE_1_0.txt"> +LICENSE_1_0.txt</a> or copy at <a href="http://www.boost.org/LICENSE_1_0.txt"> +www.boost.org/LICENSE_1_0.txt</a>)</p> + +</body> + +</html>
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