readme (14)
Václav Haisman

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 Please submit bugs, patches, feature requests, etc., there.

Tested on the following platforms

  • Linux/AMD64 with GCC 4.7.3 (Ubuntu/Linaro 4.7.3-1ubuntu1)
  • Linux/AMD64 with Sun C++ 5.12 Linux_i386 2011/11/16
  • Linux/AMD64 with Clang version 3.2-1\~exp9ubuntu1 (tags/RELEASE_32/final) (based on LLVM 3.2)
  • 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
  • Haiku R1 Alpha 4.1 with GCC 4.6.3

Configure script options


This option is disabled by default. This option mainly affects GCC builds but it also has some limited effect on non-GCC builds. It turns on debugging information generation, undefines NDEBUG symbol and adds -fstack-check (GCC).


This option is enabled by default. It adds platform / compiler dependent warning options to compiler command line.


This option is enabled by default. It enables SO version decoration on resulting library file, e.g., the .2.0.0 in


This option is enabled by default. It enables release version decoration on the resulting library file, e.g., the -1.2 in


This option is enabled by default. It enables use of compiler and platform specific option for symbols visibility. See also the Visibility page on GCC Wiki.


This option is disabled by default. This option adds profiling information generation compiler option -pg to GCC and Sun CC / Solaris Studio builds.


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.


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 BSDs.

See also docs/unicode.txt.


This is second of wchar_t \<-> char conversion related options. It is disabled by default.

It is known to work well on most Unix–like platforms, including recent Cygwin.


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 encoding. 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.


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.



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. Unfortunately, not all affected version of GCC have this option.

MinGW and MSVCRT version

log4cplus can use functions like _vsnprintf_s() (Microsoft’s secure version of vsnprintf()). MinGW tool–chains (by default) link to the system MSVCRT.DLL. Unfortunately, older systems, like Windows XP, ship with MSVCRT.DLL that lacks these functions. It is possible to compile log4cplus with MinGW tool–chains but without using the Microsoft’s secure functions by defining __MSVCRT_VERSION__ to value less than 0x900 and vice versa.

$ ../configure CPPFLAGS="-D__MSVCRT_VERSION__=0x700"

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
  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 targeted to Windows Vista or later.

Threads and signals

log4cplus is not safe to be used from asynchronous 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. 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

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 circumstances. 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 #103.

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 recursively lock the global non recursive lock and a deadlock.

Solaris / SunOS

Some older version of this operating system might have problems linking log4cplus due to missing __tls_get_addr in their unpatched state.

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 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 \

HP-UX with aCC

It is necessary to turn on C++98 mode of aCC by providing the -AA flag:

$ ../configure --enable-threads=yes CXXFLAGS="-AA"

HP-UX with aCC on IA64

There is a problem on I64 HP-UX with aCC (HP C/aC++ B3910B A.06.20). The problem manifests as unsatisfied symbols during linking of loggingserver:

ld: Unsatisfied symbol "virtual table of loggingserver::ClientThread" in file loggingserver.o

The problem appears to be a deficiency in aCC and its support of __declspec(dllexport). To work around this issue, add --disable-symbols-visibility-options to configure script command line:

$ ../configure --disable-symbols-visibility-options \
--enable-threads=yes CXXFLAGS="-AA"


Haiku is supported with GCC 4+. The default GCC version in Haiku is set to version 2 (based on GCC 2.95.x). To change the default GCC version to version 4, please run setgcc gcc4 command. This is to avoid linking errors like this:

main.cpp:(.text.startup+0x54a): undefined reference to `_Unwind_Resume'

Running the command switches the current GCC version to version 4. This change is permanent and global. See also Haiku ticket #8368.

Qt4 / Win32 / MSVC

In order to use log4cplus in Qt4 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 runtime, call this function: 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


Beware, the %s specifier does not work the same way on Unix–like platforms 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 printf(). On the other hand, Unix–like platforms 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 Unix–like platforms.

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 Unix–like platforms 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
  • Older versions of 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


This library is licensed under the Apache Public License 2.0 and two clause BSD license. Please read the included LICENSE file for details.


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