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-<div><h1 class="title">
-<a name="libstdc++-porting-howto"></a>Libstdc++-porting-howto</h1></div>
-<div><h3 class="author">Felix Natter</h3></div>
-<div><div class="legalnotice">
-<p class="legalnotice-title"><b>Legal Notice</b></p>
-<p>
- This document can be distributed under the FDL
- (<a href="http://www.gnu.org" target="_top">www.gnu.org</a>)
- </p>
-</div></div>
-<div><p class="pubdate">Tue Jun 5 20:07:49 2001</p></div>
-<div><div class="revhistory"><table border="1" width="100%" summary="Revision history">
-<tr><th align="left" valign="top" colspan="3"><b>Revision History</b></th></tr>
-<tr>
-<td align="left">Revision 0.5</td>
-<td align="left">Thu Jun 1 13:06:50 2000</td>
-<td align="left">fnatter</td>
-</tr>
-<tr><td align="left" colspan="3">First docbook-version.</td></tr>
-<tr>
-<td align="left">Revision 0.8</td>
-<td align="left">Sun Jul 30 20:28:40 2000</td>
-<td align="left">fnatter</td>
-</tr>
-<tr><td align="left" colspan="3">First released version using docbook-xml
- + second upload to libstdc++-page.
- </td></tr>
-<tr>
-<td align="left">Revision 0.9</td>
-<td align="left">Wed Sep 6 02:59:32 2000</td>
-<td align="left">fnatter</td>
-</tr>
-<tr><td align="left" colspan="3">5 new sections.</td></tr>
-<tr>
-<td align="left">Revision 0.9.1</td>
-<td align="left">Sat Sep 23 14:20:15 2000</td>
-<td align="left">fnatter</td>
-</tr>
-<tr><td align="left" colspan="3">added information about why file-descriptors are not in the
- standard</td></tr>
-<tr>
-<td align="left">Revision 0.9.2</td>
-<td align="left">Tue Jun 5 20:07:49 2001</td>
-<td align="left">fnatter</td>
-</tr>
-<tr><td align="left" colspan="3">
- a fix, added hint on increased portability of C-shadow-headers,
- added autoconf-test HAVE_CONTAINER_AT
- </td></tr>
-<tr>
-<td align="left">Revision 0.9.3</td>
-<td align="left">Fri Jun 29 16:15:56 2001</td>
-<td align="left">fnatter</td>
-</tr>
-<tr><td align="left" colspan="3">
- changed signature of nonstandard filebuf-constructor and
- update the section on filebuf::attach to point to ../ext/howto.html,
- added link to ../21/strings/howto.html
- in sec-stringstream, changed <link>-tags to have content
- (so that these links work),
- replace "user-space" by "global namespace"
- add note about gcc 3.0 and shadow-headers
- add section about ostream::form and istream::scan
- sec-vector-at: remove hint to modify headers
- fix spelling error in sec-stringstream
- </td></tr>
-<tr>
-<td align="left">Revision 0.9.4</td>
-<td align="left">Mon Nov 5 17:01:04 2001</td>
-<td align="left">fnatter</td>
-</tr>
-<tr><td align="left" colspan="3">
- rewrite section 1.1.3 because of gnu.gcc.help-post by
- Juergen Heinzl
- </td></tr>
-</table></div></div>
-<div><div class="abstract">
-<p><b>Abstract</b></p>
-<p>
- Some notes on porting applications from libstdc++-2.90 (or earlier
- versions) to libstdc++-v3. Not speaking in terms of the GNU libstdc++
- implementations, this means porting from earlier versions of the
- C++-Standard to ISO 14882.
- </p>
-</div></div>
-<hr>
-</div>
-<div class="toc">
-<p><b>Table of Contents</b></p>
-<dl>
-<dt>1. <a href="#sec-nsstd">Namespace std::</a>
-</dt>
-<dd><dl>
-<dt>1.1.1. <a href="#sec-gtkmm-hack">Using namespace
- composition if the project uses a separate
- namespace</a>
-</dt>
-<dt>1.1.2. <a href="#sec-emptyns">Defining an empty namespace std</a>
-</dt>
-<dt>1.1.3. <a href="#sec-avoidfqn">Avoid to use fully qualified names
- (i.e. std::string)</a>
-</dt>
-<dt>1.1.4. <a href="#sec-osprojects">How some open-source-projects deal
- with this</a>
-</dt>
-</dl></dd>
-<dt>2. <a href="#sec-nocreate">there is no ios::nocreate/ios::noreplace
- in ISO 14882</a>
-</dt>
-<dt>3. <a href="#sec-stream::attach">stream::attach(int
- fd) is not in the standard any more</a>
-</dt>
-<dt>4. <a href="#sec-headers">The new headers</a>
-</dt>
-<dd><dl>
-<dt>4.4.1. <a href="#sec-cheaders">New headers replacing C-headers</a>
-</dt>
-<dt>4.4.2. <a href="#sec-fstream-header">
- <fstream> does
- not define std::cout,
- std::cin etc.</a>
-</dt>
-</dl></dd>
-<dt>5. <a href="#sec-iterators">Iterators</a>
-</dt>
-<dt>6. <a href="#sec-macros">
- Libc-macros (i.e. isspace from
- <cctype>)</a>
-</dt>
-<dt>7. <a href="#sec-stream-state">State of streams</a>
-</dt>
-<dt>8. <a href="#sec-vector-at">vector::at is missing (i.e. gcc 2.95.x)</a>
-</dt>
-<dt>9. <a href="#sec-eof">Using std::char_traits<char>::eof()</a>
-</dt>
-<dt>10. <a href="#sec-string-clear">Using string::clear()/string::erase()</a>
-</dt>
-<dt>11. <a href="#sec-scan-form">GNU Extensions ostream::form and istream::scan</a>
-</dt>
-<dt>12. <a href="#sec-stringstream">Using stringstreams</a>
-</dt>
-<dt>13. <a href="#sec-about">About...</a>
-</dt>
-</dl>
-</div>
-<p>
- In the following, when I say portable, I will refer to "portable among ISO
- 14882-implementations". On the other hand, if I say "backportable" or
- "conservative", I am talking about "compiles with older
- libstdc++-implementations".
- </p>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-nsstd"></a>Namespace std::</h2></div></div>
-<p>
- The latest C++-standard (ISO-14882) requires that the standard
- C++-library is defined in namespace std::. Thus, in order to use
- classes from the standard C++-library, you can do one of three
- things:
- <div class="itemizedlist"><ul type="disc">
-<li><p>wrap your code in <b>namespace std {
- ... }</b> => This is not an option because only symbols
- from the standard c++-library are defined in namespace std::.
- </p></li>
-<li><p>put a kind of
- <span class="emphasis"><i>using-declaration</i></span> in your source (either
- <b>using namespace std;</b> or i.e. <b>using
- std::string;</b>) => works well for source-files, but
- cannot be used in header-files.
- </p></li>
-<li><p>use a <span class="emphasis"><i>fully qualified name</i></span> for
- each libstdc++-symbol (i.e. <b>std::string</b>,
- <b>std::cout</b>) => can always be used
- </p></li>
-</ul></div>
- </p>
-<p>
- Because there are many compilers which still use an implementation
- that does not have the standard C++-library in namespace
- <b>std::</b>, some care is required to support these as
- well.
- </p>
-<p>
- Namespace back-portability-issues are generally not a problem with
- g++, because versions of g++ that do not have libstdc++ in
- <b>std::</b> use <b>-fno-honor-std</b>
- (ignore <b>std::</b>, <b>:: = std::</b>) by
- default. That is, the responsibility for enabling or disabling
- <b>std::</b> is on the user; the maintainer does not have
- to care about it. This probably applies to some other compilers as
- well.
- </p>
-<p>
- The following sections list some possible solutions to support compilers
- that cannot ignore std::.
- </p>
-<div class="section">
-<div class="titlepage"><div><h3 class="title">
-<a name="sec-gtkmm-hack"></a>Using <span class="emphasis"><i>namespace
- composition</i></span> if the project uses a separate
- namespace</h3></div></div>
-<p>
- <a href="http://gtkmm.sourceforge.net" target="_top">Gtk--</a> defines
- most of its classes in namespace Gtk::. Thus, it was possible to
- adapt Gtk-- to namespace std:: by using a C++-feature called
- <span class="emphasis"><i>namespace composition</i></span>. This is what happens if
- you put a <span class="emphasis"><i>using</i></span>-declaration into a
- namespace-definition: the imported symbol(s) gets imported into the
- currently active namespace(s). For example:
- <pre class="programlisting">
- namespace Gtk {
- using std::string;
- class Window { ... }
- }
- </pre>
- In this example, <b>std::string</b> gets imported into
- namespace Gtk::. The result is that you don't have to use
- <b>std::string</b> in this header, but still
- <b>std::string</b> does not get imported into
- the global namespace (::) unless the user does
- <b>using namespace Gtk;</b> (which is not recommended
- practice for Gtk--, so it is not a problem). Additionally, the
- <b>using</b>-declarations are wrapped in macros that
- are set based on autoconf-tests to either "" or i.e. <b>using
- std::string;</b> (depending on whether the system has
- libstdc++ in <b>std::</b> or not). (ideas from
- <tt><<a href="mailto:llewelly@dbritsch.dsl.xmission.com">llewelly@dbritsch.dsl.xmission.com</a>></tt>, Karl Nelson
- <tt><<a href="mailto:kenelson@ece.ucdavis.edu">kenelson@ece.ucdavis.edu</a>></tt>)
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h3 class="title">
-<a name="sec-emptyns"></a>Defining an empty namespace std</h3></div></div>
-<p>
- By defining an (empty) namespace <b>std::</b> before
- using it, you avoid getting errors on systems where no part of the
- library is in namespace std:
- <pre class="programlisting">
- namespace std { }
- using namespace std;
- </pre>
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h3 class="title">
-<a name="sec-avoidfqn"></a>Avoid to use fully qualified names
- (i.e. std::string)</h3></div></div>
-<p>
- If some compilers complain about <b>using
- std::string;</b>, and if the "hack" for gtk-- mentioned above
- does not work, then I see two solutions:
-
- <div class="itemizedlist"><ul type="disc">
-<li><p>
- Define <b>std::</b> as a macro if the compiler
- doesn't know about <b>std::</b>.
- <pre class="programlisting">
- #ifdef OLD_COMPILER
- #define std
- #endif
- </pre>
- (thanks to Juergen Heinzl who posted this solution on
- gnu.gcc.help)
- </p></li>
-<li><p>
- Define a macro NS_STD, which is defined to
- either "" or "std"
- based on an autoconf-test. Then you should be able to use
- <b>NS_STD::string</b>, which will evaluate to
- <b>::string</b> ("string in the global namespace") on
- systems that do not put string in std::. (This is untested)
- </p></li>
-</ul></div>
-
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h3 class="title">
-<a name="sec-osprojects"></a>How some open-source-projects deal
- with this</h3></div></div>
-<p>
- This information was gathered around May 2000. It may not be correct
- by the time you read this.
- </p>
-<div class="table">
-<p><b>Table 1. Namespace std:: in Open-Source programs</b></p>
-<table summary="Namespace std:: in Open-Source programs" border="1">
-<colgroup>
-<col>
-<col>
-</colgroup>
-<tbody>
-<tr>
-<td><a href="http://www.clanlib.org" target="_top">clanlib</a></td>
-<td>usual</td>
-</tr>
-<tr>
-<td><a href="http://pingus.seul.org" target="_top">pingus</a></td>
-<td>usual</td>
-</tr>
-<tr>
-<td><a href="http://www.mozilla.org" target="_top">mozilla</a></td>
-<td>usual</td>
-</tr>
-<tr>
-<td><a href="http://www.mnemonic.org" target="_top">mnemonic</a></td>
-<td>none</td>
-</tr>
-<tr>
-<td><a href="http://libsigc.sourceforge.net" target="_top">
- libsigc++</a></td>
-<td>conservative-impl</td>
-</tr>
-</tbody>
-</table>
-</div>
-<div class="table">
-<p><b>Table 2. Notations for categories</b></p>
-<table summary="Notations for categories" border="1">
-<colgroup>
-<col>
-<col>
-</colgroup>
-<tbody>
-<tr>
-<td>usual</td>
-<td>mostly fully qualified names and some
- using-declarations (but not in headers)</td>
-</tr>
-<tr>
-<td>none</td>
-<td>no namespace std at all</td>
-</tr>
-<tr>
-<td>conservative-impl</td>
-<td>wrap all
- namespace-handling in macros to support compilers without
- namespace-support (no libstdc++ used in headers)</td>
-</tr>
-</tbody>
-</table>
-</div>
-<p>
- As you can see, this currently lacks an example of a project
- which uses libstdc++-symbols in headers in a back-portable way
- (except for Gtk--: see the <a href="#sec-gtkmm-hack" title="Using namespace
- composition if the project uses a separate
- namespace">section on the gtkmm-hack</a>).
- </p>
-</div>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-nocreate"></a>there is no ios::nocreate/ios::noreplace
- in ISO 14882</h2></div></div>
-<p>
- I have seen <b>ios::nocreate</b> being used for
- input-streams, most probably because the author thought it would be
- more correct to specify nocreate "explicitly". So you can simply
- leave it out for input-streams.
- </p>
-<p>
- For output streams, "nocreate" is probably the default, unless you
- specify <b>std::ios::trunc</b> ? To be safe, you can open
- the file for reading, check if it has been opened, and then decide
- whether you want to create/replace or not. To my knowledge, even
- older implementations support <b>app</b>,
- <b>ate</b> and <b>trunc</b> (except for
- <b>app</b> ?).
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-stream::attach"></a><b>stream::attach(int
- fd)</b> is not in the standard any more</h2></div></div>
-<p>
- Phil Edwards <tt><<a href="mailto:pedwards@disaster.jaj.com">pedwards@disaster.jaj.com</a>></tt> writes:
- It was considered and rejected. Not all environments use file
- descriptors. Of those that do, not all of them use integers to represent
- them.
- </p>
-<p>
- When using libstdc++-v3, you can use
- <div class="funcsynopsis">
-<pre class="funcsynopsisinfo">
- #include <fstream>
- </pre>
-<p><code><code class="funcdef">
- <b class="fsfunc">basic_filebuf<...>::basic_filebuf<...>
- </b>
- </code>(<var class="pdparam">file</var>, <var class="pdparam">mode</var>, <var class="pdparam">size</var>);<br>__c_file_type* <var class="pdparam">file</var>;<br>ios_base::open_mode <var class="pdparam">mode</var>;<br>int <var class="pdparam">size</var>;</code></p>
-</div>
- but the the signature of this constructor has changed often, and
- it might change again. For the current state of this, check
- <a href="../ext/howto.html" target="_top">the howto for extensions</a>.
- </p>
-<p>
- For a portable solution (among systems which use
- filedescriptors), you need to implement a subclass of
- <b>std::streambuf</b> (or
- <b>std::basic_streambuf<..></b>) which opens a file
- given a descriptor, and then pass an instance of this to the
- stream-constructor. For an example of this, refer to
- <a href="http://www.josuttis.com/cppcode/fdstream.html" target="_top">fdstream example</a>
- by Nicolai Josuttis.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-headers"></a>The new headers</h2></div></div>
-<p>
- All new headers can be seen in this <a href="headers_cc.txt" target="_top">
- source-code</a>.
- </p>
-<p>
- The old C++-headers (iostream.h etc.) are available, but gcc generates
- a warning that you are using deprecated headers.
- </p>
-<div class="section">
-<div class="titlepage"><div><h3 class="title">
-<a name="sec-cheaders"></a>New headers replacing C-headers</h3></div></div>
-<p>
- You should not use the C-headers (except for system-level
- headers) from C++ programs. Instead, you should use a set of
- headers that are named by prepending 'c' and, as usual,
- omitting the extension (.h). For example, instead of using
- <tt><math.h></tt>, you
- should use <tt><cmath></tt>. In some cases this has
- the advantage that the C++-header is more standardized than
- the C-header (i.e. <tt><ctime></tt> (almost)
- corresponds to either <tt><time.h></tt> or <tt><sys/time.h></tt>).
-
- The standard specifies that if you include the C-style header
- (<tt><math.h></tt> in
- this case), the symbols will be available both in the global
- namespace and in namespace <b>std::</b> (but
- libstdc++ does not yet have fully compliant headers) On the
- other hand, if you include only the new header (i.e. <tt><cmath></tt>), the symbols
- will only be defined in namespace <b>std::</b>
- (and macros will be converted to inline-functions).
- </p>
-<p>
- For more information on this, and for information on how the
- GNU C++ implementation might reuse ("shadow") the C
- library-functions, have a look at <a href="http://www.cantrip.org/cheaders.html" target="_top">
- www.cantrip.org</a>.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h3 class="title">
-<a name="sec-fstream-header"></a>
- <tt><fstream></tt> does
- not define <b>std::cout</b>,
- <b>std::cin</b> etc.</h3></div></div>
-<p>
- In earlier versions of the standard,
- <tt><fstream.h></tt>,
- <tt><ostream.h></tt>
- and <tt><istream.h></tt>
- used to define
- <b>cout</b>, <b>cin</b> and so on. Because
- of the templatized iostreams in libstdc++-v3, you need to include
- <tt><iostream></tt>
- explicitly to define these.
- </p>
-</div>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-iterators"></a>Iterators</h2></div></div>
-<p>
- The following are not proper uses of iterators, but may be working
- fixes for existing uses of iterators.
- <div class="itemizedlist"><ul type="disc">
-<li><p>you cannot do
- <b>ostream::operator<<(iterator)</b> to
- print the address of the iterator => use
- <b>operator<< &*iterator</b> instead ?
- </p></li>
-<li><p>you cannot clear an iterator's reference
- (<b>iterator = 0</b>) => use
- <b>iterator = iterator_type();</b> ?
- </p></li>
-<li><p>
-<b>if (iterator)</b> won't work any
- more => use <b>if (iterator != iterator_type())</b>
- ?</p></li>
-</ul></div>
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-macros"></a>
- Libc-macros (i.e. <b>isspace</b> from
- <tt><cctype></tt>)</h2></div></div>
-<p>
- Glibc 2.0.x and 2.1.x define the
- <tt><ctype.h></tt>
- -functionality as macros (isspace, isalpha etc.). Libstdc++-v3
- "shadows" these macros as described in the <a href="#sec-cheaders" title="New headers replacing C-headers">section about
- c-headers</a>.
- </p>
-<p>
- Older implementations of libstdc++ (g++-2 for egcs 1.x and g++-3
- for gcc 2.95.x), however, keep these functions as macros, and so it
- is not back-portable to use fully qualified names. For example:
- <pre class="programlisting">
- #include <cctype>
- int main() { std::isspace('X'); }
- </pre>
- will result in something like this (unless using g++-v3):
- <pre class="programlisting">
- std:: (__ctype_b[(int) ( ( 'X' ) )] & (unsigned short int)
- _ISspace ) ;
- </pre>
- </p>
-<p>
- One solution I can think of is to test for -v3 using
- autoconf-macros, and define macros for each of the C-functions
- (maybe that is possible with one "wrapper" macro as well ?).
- </p>
-<p>
- Another solution which would fix g++ is to tell the user to modify a
- header-file so that g++-2 (egcs 1.x) and g++-3 (gcc 2.95.x) define a
- macro which tells <tt><ctype.h></tt> to define functions
- instead of macros:
- <pre class="programlisting">
- // This keeps isalnum, et al from being propagated as macros.
- #if __linux__
- #define __NO_CTYPE 1
- #endif
-
- [ now include <ctype.h> ]
- </pre>
- </p>
-<p>
- Another problem arises if you put a <b>using namespace
- std;</b> declaration at the top, and include <tt><ctype.h></tt>. This will result in
- ambiguities between the definitions in the global namespace
- (<tt><ctype.h></tt>) and the
- definitions in namespace <b>std::</b>
- (<b><cctype></b>).
- </p>
-<p>
- The solution to this problem was posted to the libstdc++-v3
- mailing-list:
- Benjamin Kosnik <tt><<a href="mailto:bkoz@redhat.com">bkoz@redhat.com</a>></tt> writes:
- ‘
- --enable-cshadow-headers is currently broken. As a result, shadow
- headers are not being searched....
- ’
- This is now outdated, but gcc 3.0 still does not have fully
- compliant "shadow headers".
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-stream-state"></a>State of streams</h2></div></div>
-<p>
- At least some older implementations don't have
- <b>std::ios_base</b>, so you should use
- <b>std::ios::badbit</b>, <b>std::ios::failbit</b>
- and <b>std::ios::eofbit</b> and
- <b>std::ios::goodbit</b>.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-vector-at"></a>vector::at is missing (i.e. gcc 2.95.x)</h2></div></div>
-<p>
- One solution is to add an autoconf-test for this:
- <pre class="programlisting">
- AC_MSG_CHECKING(for container::at)
- AC_TRY_COMPILE(
- [
- #include <vector>
- #include <deque>
- #include <string>
-
- using namespace std;
- ],
- [
- deque<int> test_deque(3);
- test_deque.at(2);
- vector<int> test_vector(2);
- test_vector.at(1);
- string test_string("test_string");
- test_string.at(3);
- ],
- [AC_MSG_RESULT(yes)
- AC_DEFINE(HAVE_CONTAINER_AT)],
- [AC_MSG_RESULT(no)])
- </pre>
- If you are using other (non-GNU) compilers it might be a good idea
- to check for <b>string::at</b> separately.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-eof"></a>Using std::char_traits<char>::eof()</h2></div></div>
-<p>
- <pre class="programlisting">
- #ifdef HAVE_CHAR_TRAITS
- #define CPP_EOF std::char_traits<char>::eof()
- #else
- #define CPP_EOF EOF
- #endif
- </pre>
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-string-clear"></a>Using string::clear()/string::erase()</h2></div></div>
-<p>
- There are two functions for deleting the contents of a string:
- <b>clear</b> and <b>erase</b> (the latter
- returns the string).
- <pre class="programlisting">
- void
- clear() { _M_mutate(0, this->size(), 0); }
- </pre>
- <pre class="programlisting">
- basic_string&
- erase(size_type __pos = 0, size_type __n = npos)
- {
- return this->replace(_M_check(__pos), _M_fold(__pos, __n),
- _M_data(), _M_data());
- }
- </pre>
- The implementation of <b>erase</b> seems to be more
- complicated (from libstdc++-v3), but <b>clear</b> is not
- implemented in gcc 2.95.x's libstdc++, so you should use
- <b>erase</b> (which is probably faster than
- <b>operator=(charT*)</b>).
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-scan-form"></a>GNU Extensions ostream::form and istream::scan</h2></div></div>
-<p>
- These are not supported any more - use
- <a href="#sec-stringstream" title="Using stringstreams">
- stringstreams</a> instead.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-stringstream"></a>Using stringstreams</h2></div></div>
-<p>
- Libstdc++-v3 provides the new
- <b>i/ostringstream</b>-classes, (<tt><sstream></tt>), but for compatibility
- with older implementations you still have to use
- <b>i/ostrstream</b> (<tt><strstream></tt>):
- <pre class="programlisting">
- #ifdef HAVE_SSTREAM
- #include <sstream>
- #else
- #include <strstream>
- #endif
- </pre>
- <div class="itemizedlist"><ul type="disc">
-<li><p> <b>strstream</b> is considered to be
- deprecated
- </p></li>
-<li><p> <b>strstream</b> is limited to
- <b>char</b>
- </p></li>
-<li><p> with <b>ostringstream</b> you don't
- have to take care of terminating the string or freeing its
- memory
- </p></li>
-<li><p> <b>istringstream</b> can be re-filled
- (clear(); str(input);)
- </p></li>
-</ul></div>
- </p>
-<p>
- You can then use output-stringstreams like this:
- <pre class="programlisting">
- #ifdef HAVE_SSTREAM
- std::ostringstream oss;
- #else
- std::ostrstream oss;
- #endif
- oss << "Name=" << m_name << ", number=" << m_number << std::endl;
- ...
- #ifndef HAVE_SSTREAM
- oss << std::ends; // terminate the char*-string
- #endif
- // str() returns char* for ostrstream and a string for ostringstream
- // this also causes ostrstream to think that the buffer's memory
- // is yours
- m_label.set_text(oss.str());
- #ifndef HAVE_SSTREAM
- // let the ostrstream take care of freeing the memory
- oss.freeze(false);
- #endif
- </pre>
- </p>
-<p>
- Input-stringstreams can be used similarly:
- <pre class="programlisting">
- std::string input;
- ...
- #ifdef HAVE_SSTREAM
- std::istringstream iss(input);
- #else
- std::istrstream iss(input.c_str());
- #endif
- int i;
- iss >> i;
- </pre>
- One (the only?) restriction is that an istrstream cannot be re-filled:
- <pre class="programlisting">
- std::istringstream iss(numerator);
- iss >> m_num;
- // this is not possible with istrstream
- iss.clear();
- iss.str(denominator);
- iss >> m_den;
- </pre>
- If you don't care about speed, you can put these conversions in
- a template-function:
- <pre class="programlisting">
- template <class X>
- void fromString(const string& input, X& any)
- {
- #ifdef HAVE_SSTREAM
- std::istringstream iss(input);
- #else
- std::istrstream iss(input.c_str());
- #endif
- X temp;
- iss >> temp;
- if (iss.fail())
- throw runtime_error(..)
- any = temp;
- }
- </pre>
- Another example of using stringstreams is in <a href="../21_strings/howto.html" target="_top">this howto</a>.
- </p>
-<p>
- I have read the Josuttis book on Standard C++, so some information
- comes from there. Additionally, there is information in
- "info iostream", which covers the old implementation that gcc 2.95.x
- uses.
- </p>
-</div>
-<div class="section">
-<div class="titlepage"><div><h2 class="title" style="clear: both">
-<a name="sec-about"></a>About...</h2></div></div>
-<p>
- Please send any experience, additions, corrections or questions to
- <a href="mailto:fnatter@gmx.net" target="_top">fnatter@gmx.net</a> or for
- discussion to the libstdc++-v3-mailing-list.
- </p>
-</div>
-</div></body>
-</html>