Short Description
=================
log4cplus is a simple to use C++ logging API providing thread-safe,
flexible, and arbitrarily granular control over log management and
configuration. It is modeled after the Java log4j API.
Latest Project Information
==========================
The latest up-to-date information for this project can be found at
http://log4cplus.sourceforge.net. Please submit bugs, patches,
feature requests, etc. there.
Tested on the following platforms
=================================
- Linux/AMD64 with GCC 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)
- Linux/AMD64 with Sun C++ 5.12 Linux_i386 2011/11/16
- Linux/AMD64 with Clang version 3.0-6ubuntu3 (tags/RELEASE_30/final)
(based on LLVM 3.0)
- Linux/AMD64 with Intel(R) C++ Intel(R) 64 Compiler XE for
applications running on Intel(R) 64, Version 12.1 Build 20120410
- FreeBSD/AMD64 with GCC 3.4.6, 4.2.1 and 4.3.3
- Windows 7 with MS Visual C++ 10.0
- OpenSolaris 5.11 with Sun C++ 5.10 SunOS_i386 128229-02 2009/09/21,
with -library=stlport4
- Solaris 5.10 with Sun C++ 5.8 2005/10/13, with -library=stlport4
- NetBSD 5.0.2/AMD64 with GCC 4.1.3 20080704 prerelease (NetBSD nb2
20081120)
- OpenBSD 5.0/AMD64 with GCC 4.2.1 20070719
Configure script options
========================
--enable-debugging
------------------
This option is disabled by default. This option mainly affects GCC
builds but it also has some limitted effect on non-GCC builds. It
turns on debugging information generation, undefines NDEBUG symbol,
adds '-fkeep-inline-functions' and '-fstack-check' (GCC).
--enable-warnings
-----------------
This option is enabled by default. It adds platform / compiler
dependent warning options to compiler command line.
--enable-profiling
------------------
This option is disabled by default. This option adds profiling
information generation compiler option -pg to GCC and Sun CC / Solaris
Studio builds.
--enable-threads
----------------
This option is enabled by default. It turns on detection of necessary
compiler and linker flags that enable POSIX threading support.
While this detection usually works well, some platforms still need
help with configuration by supplying additional flags to the configure
script. One of the know deficiencies is Solaris Studio on Linux. See
one of the later note for details.
--with-working-locale
---------------------
This is one of three locale and wchar_t <-> char conversion related
options. It is disabled by default.
It is know to work well with GCC on Linux. Other platforms generally
have lesser locale support in their implementations of the C++
standard library. It is known not to work well on any *BSD.
See also docs/unicode.txt.
--with-working-c-locale
-----------------------
This is second of wchar_t <-> char conversion related options. It is
disabled by default.
It is known to work well on most *NIX platforms, including recent Cygwin.
--with-iconv
------------
This is third of wchar_t <-> char conversion related options. It is
disabled by default.
The conversion using iconv() function always uses "UTF-8" and
"WCHAR_T" as source/target encodings. It is known to work well on
platforms with GNU iconv. Different implementations of iconv() might
not support "WCHAR_T" encoding selector.
Either system provided iconv() or library provided libiconv() are
detected and accepted. Also both SUSv3 and GNU iconv() function
signatures are accepted.
--with-qt
---------
This option is disabled by default. It enables compilation of a
separate shared library (liblog4cplusqt4debugappender) that implements
Qt4DebugAppender. It requires Qt4 and pkg-config to be installed.
Notes
=====
Cygwin/MinGW
------------
Some version of GCC (3.4.x and probably some of 4.x series too) on
Windows (both Mingw and Cygwin) produces lots of warnings of the form
"warning: inline function 'void foo()' is declared as dllimport:
attribute ignored." This can be worked around by adding
-Wno-attributes option to GCC command. Unfortunatelly, not all
affected version of GCC have this option.
Windows and TLS
---------------
log4cplus uses thread-local storage (TLS) for NDC, MDC and to optimize
use of some temporary objects. On Windows there are two ways to get
TLS: (1) using TlsAlloc() etc. functions, and (2) using
__declspec(thread). While method (2) generates faster code, it has
some limitations prior to Windows Vista. If log4cplus.dll is loaded
at run time using LoadLibrary() (or as a dependency of such loaded
library), then accessing __declspec(thread) variables can cause
general protection fault (GPF) errors. This is because Windows prior
to Windows Vista do not extend the TLS for libraries loaded at run
time using LoadLibrary(). To allow using the best available method,
log4cplus enables the method (2) by checking _WIN32_WINNT >= 0x0600
condition, when compiling log4cplus targetted to Windows Vista or
later.
Threads and signals
-------------------
log4cplus is not safe to be used from async signals' handlers. This
is a property of most threaded programmes in general. If you are
going to use log4cplus in threaded application and if you want to use
log4cplus from signal handlers then your only option is to block
signals in all threads but one that will handle all signals. On POSIX
platforms, this is possible using the sigwait() call. log4cplus
enables this approach by blocking all signals in any threads created
through its threads helpers.
IBM's XL C/C++ compiler
-----------------------
IBM's XL C/C++ compiler executable has many variants ([1]). To
compile log4cplus with threading support specify one of the compiler
variants that support threading using the CXX variable on configure
script command line. E.g.:
$ ../configure --enable-threads CXX=xlC_r
[1] <http://pic.dhe.ibm.com/infocenter/comphelp/v121v141/index.jsp?topic=%2Fcom.ibm.xlcpp121.aix.doc%2Fcompiler_ref%2Ftucmpinv.html>
AIX reentrancy problem
----------------------
There appears to be a reentracy problem with AIX 5.3 and xlC 8 which
can result into a deadlock condition in some curcumstances. It is
unknown whether the problem manifests with other versions of either
the OS or the compiler, too. The problem was initially reported in a
bug report #3056687 ([1]).
The core of the problem is that IBM's/xlC's standard C++ IOStreams
implementation uses global non recursive lock to protect some of its
state. The application in the bug report was trying to do logging
using log4cplus from inside overflow() member function of a class
derived from std::streambuf class. log4cplus itself uses
std::ostringstream. This resulted into an attempt to recursivly lock
the global non recursive lock and a deadlock.
[1] <https://sourceforge.net/tracker/?func=detail&aid=3056687&group_id=40830&atid=429073>
Solaris / SunOS
---------------
Some older version of this operating system might have problems
linking log4cplus due to missing __tls_get_addr ([1]) in their
unpatched state.
[1] <https://groups.google.com/d/msg/comp.unix.solaris/AAMqkK0QZ6U/zlkVKA1L_QcJ>
Solaris Studio
--------------
Solaris Studio compilers' default standard C++ library is very
non-standard. It seems that it is not conforming enough in, e.g., Sun
C++ 5.12 Linux_i386 2011/11/16 (missing std::time_t, etc.), but it
works well enough on Solaris with Sun C++ 5.8 2005/10/13. Thus
log4cplus adds -library=stlport4 to the CXXFLAGS environment variable,
unless a switch matching -library=(stlport4|stdcxx4|Cstd) is already
present there. If you want to override the default supplied by
log4cplus, just set it into CXXFLAGS on configure script command line.
Solaris Studio supports the __func__ symbol which can be used by
log4cplus to record function name in logged events. To enable this
feature, add '-features=extensions' switch to CXXFLAGS for configure
script. Subsequently, you will have to add this switch to your
application's build flags as well.
Solaris Studio on GNU/Linux
---------------------------
The autotools and our configure.in combo does not handle Solaris
Studio compiler on Linux well enough and needs a little help with
configuration of POSIX threads:
$ COMMON_FLAGS="-L/lib/x86_64-linux-gnu/ -L/usr/lib/x86_64-linux-gnu/ \
-mt=yes -O"
$ ../configure --enable-threads=yes CC=/opt/solarisstudio12.3/bin/cc \
CXX=/opt/solarisstudio12.3/bin/CC CFLAGS="$COMMON_FLAGS" \
CXXFLAGS="$COMMON_FLAGS" LDFLAGS="-lpthread"
Qt / Win32 / MSVC
-----------------
In order to use log4cplus in Qt programs it is necessary to set
following option:
Treat WChar_t As Built in Type: No (/Zc:wchar_t-)
Set this option for log4cplus project and Qt4DebugAppender project in
MS Visual Studio. Remember to use Unicode versions of log4cplus
libraries with Qt. It is also necessary to make clear distinction
between debug and release builds of Qt project and log4cplus. Do not
use log4cplus release library with debug version of Qt program or vice
versa.
For registering Qt4DebugAppender library at run-time call this method:
log4cplus::Qt4DebugAppender::registerAppender() ;
Add these lines to qmake project file for using log4cplus and
Qt4DebugAppender:
INCLUDEPATH += C:\log4cplus\include
win32 {
CONFIG(debug, debug|release) {
LIBS += -LC:\log4cplus\msvc10\Win32\bin.Debug_Unicode -llog4cplusUD
LIBS += -LC:\log4cplus\msvc10\Win32\bin.Debug_Unicode -llog4cplus-Qt4DebugAppender
} else {
LIBS += -LC:\log4cplus\msvc10\Win32\bin.Release_Unicode -llog4cplusU
LIBS += -LC:\log4cplus\msvc10\Win32\bin.Release_Unicode -llog4cplus-Qt4DebugAppender
}
}
LOG4CPLUS_*_FMT() and UNICODE
-----------------------------
Beware, the %s specifier does not work the same way on *NIX as it does
on Windows with Visual Studio. With Visual Studio the %s specifier
changes its meaning conveniently by printing wchar_t string when used
with wprintf() and char strings when used with wprintf(). On the
other hand, *NIX keeps the meaning of printing char strings when used
with both wprintf() and printf(). It is necessary to use %ls (C99)
specifier or %S (SUSv2) specifier to print wchar_t strings on *NIX.
The common ground for both platforms appears to be use of %ls and
wchar_t string to print strings with unmodified formatting string
argument on both *NIX and Windows. The conversion of wchar_t back to
char then depends on C locale.
C++11 support
-------------
log4cplus contains small amount of code that uses C++11 (ISO/IEC
14882:2011 standard) language features. C++11 features are used only
if C++11 support is detected during compile time. Compiling log4cplus
with C++11 compiler and standard library and using it with C++03
(ISO/IEC 14882:2003 standard) application is not supported.
Unsupported compilers
---------------------
log4cplus does not support too old or broken C++ compilers:
- Visual C++ prior to 7.1
- GCC prior to 3.2
- All Borland/CodeGear/Embarcadero C++ compilers
Unsupported platforms
---------------------
log4cplus requires some minimal set of C and/or C++ library
functions. Some systems/platforms fail to provide these functions and
thus log4cplus cannot be supported there:
- Windows CE - missing implementations of <time.h> functions
License
=======
This library is licensed under the Apache Public License 2.0 and two
clause BSD license. Please read the included LICENSE file for
details.
