Linux混合编程+log4cpp

 

     由于要使用到log4cpp的库，而log4c的资料是非常的少，也懒得去研究它的用法，于是就决定试试混合编程者玩意。

      首先先引用下C++它的father: Stroustrup的一篇文章《C++ Style and Technique FAQ》（http://www2.research.att.com/~bs/bs_faq2.html）里的一小个片段：

 

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Just declare the C function ``extern "C"'' (in your C++ code) and call it (from your C or C++ code). For example:

// C++ codeextern "C" void f(int);// one wayextern "C" {// another wayint g(double);double h();};void code(int i, double d){f(i);int ii = g(d);double dd = h();// ...}

The definitions of the functions may look like this:

/* C code: */void f(int i){/* ... */}int g(double d){/* ... */}double h(){/* ... */}

Note that C++ type rules, not C rules, are used. So you can't call function declared ``extern "C"'' with the wrong number of argument. For example:

// C++ codevoid more_code(int i, double d){double dd = h(i,d);// error: unexpected arguments// ...}

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Just declare the C++ function ``extern "C"'' (in your C++ code) and call it (from your C or C++ code). For example:

// C++ code:extern "C" void f(int);void f(int i){// ...}

Now f() can be used like this:

/* C code: */void f(int);void cc(int i){f(i);/* ... */}

Naturally, this works only for non-member functions. If you want to call member functions (incl. virtual functions) from C, you need to provide a simple wrapper. For example:

// C++ code:class C {// ...virtual double f(int);};extern "C" double call_C_f(C* p, int i)// wrapper function{return p->f(i);}

Now C::f() can be used like this:

/* C code: */double call_C_f(struct C* p, int i);void ccc(struct C* p, int i){double d = call_C_f(p,i);/* ... */}

If you want to call overloaded functions from C, you must provide wrappers with distinct names for the C code to use. For example:

// C++ code:void f(int);void f(double);extern "C" void f_i(int i) { f(i); }extern "C" void f_d(double d) { f(d); }

Now the f() functions can be used like this:

/* C code: */void f_i(int);void f_d(double);void cccc(int i,double d){f_i(i);f_d(d);/* ... */}

 

Note that these techniques can be used to call a C++ library from C code even if you cannot (or do not want to) modify the C++ headers.

 

      由于咱是用到c调用c++，暂不关心c++调用c的部分，如上可知，要调用c++类的成员函数，那可是麻烦的麻烦。于是还是乖乖写个函数封装一下类。

 

      由于log4cpp的调用日志比较麻烦，不像log4j，每次都要初始化一大堆东西，于是自己就把这些东西封装成了一个类为Log4cppBase：

 

Here is code:

 

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Log4cppBase.h

 

#ifndef LOG4CPPBASE_H#define LOG4CPPBASE_H#include <iostream>#include "log4cpp/Category.hh"#include "log4cpp/PropertyConfigurator.hh"#include <stdarg.h>/**author: Lan Zhihong from xmu soft*/class Log4cppBase{protected:Log4cppBase(){try{log4cpp::PropertyConfigurator::configure("log4cpp/log4cpp.conf");}catch(log4cpp::ConfigureFailure& f){std::cout << "Configure Problem" << f.what() << std::endl;}iRoot = &log4cpp::Category::getRoot();iSub = &log4cpp::Category::getInstance(std::string("sub1"));}private:Log4cppBase& operator=(Log4cppBase&);Log4cppBase(const Log4cppBase&);public:~Log4cppBase();static Log4cppBase* getInstance();static std::string vform(const char* format, va_list args);void info(const std::string& msg);void debug(const std::string& msg);void notice(const std::string& msg);void warn(const std::string& msg);void error(const std::string& msg);void crit(const std::string& msg);void alert(const std::string& msg);void emerg(const std::string& msg);void fatal(const std::string& msg);private:static Log4cppBase *iInstance;log4cpp::Category *iSub;log4cpp::Category *iRoot;};#endif

 

 

Log4cppBase.cpp

 

 

 #include "Log4cppBase.h"#include <sstream>#include <stdio.h>#define VSNPRINTF vsnprintfLog4cppBase* Log4cppBase::iInstance = 0;Log4cppBase::~Log4cppBase(){if( iSub != NULL ){delete iSub;iSub = NULL;}if( iRoot != NULL){delete iRoot;iRoot = NULL;}if( iInstance != NULL){delete iInstance;iInstance = NULL;}}Log4cppBase* Log4cppBase::getInstance(){if( iInstance == 0)iInstance = new Log4cppBase();return iInstance;}std::string Log4cppBase::vform(const char* format, va_list args){size_t size = 1024;char* buffer = new char[size]; while (1) { int n = VSNPRINTF(buffer, size, format, args); // If that worked, return a string. if ((n > -1) && (static_cast<size_t>(n) < size)) {std::string s(buffer);delete [] buffer;return s; } // Else try again with more space. size = (n > -1) ? n + 1 : // ISO/IEC 9899:1999 size * 2; // twice the old size delete [] buffer; buffer = new char[size];}}void Log4cppBase::info(const std::string& msg){iSub->info(msg); /*va_list va;va_start(va, msg);iSub->info(vform(msg, va));va_end(va);*/}void Log4cppBase::debug(const std::string& msg){iSub->info(msg);}void Log4cppBase::notice(const std::string& msg){iSub->notice(msg);}void Log4cppBase::warn(const std::string& msg){iSub->warn(msg);}void Log4cppBase::error(const std::string& msg){iSub->error(msg);}void Log4cppBase::crit(const std::string& msg){iSub->crit(msg);}void Log4cppBase::alert(const std::string& msg){iSub->alert(msg);}void Log4cppBase::emerg(const std::string& msg){iSub->emerg(msg);}void Log4cppBase::fatal(const std::string& msg){iSub->fatal(msg);}/*int main(int argc, char** argv){Log4cppBase* instance = Log4cppBase::getInstance();int i = 5;instance->info("hello world");return 0;}*/

 

 

由于选择了调用c++的非成员函数，于是由添加了这样的一个类Log4cppUtil

 

Here is code:

 

Log4cppUtil.h

 

#ifdef _cplusplusextern "C"{#endifvoid log4cpp_info(const char *msg, ...);#ifdef _cplusplus}#endif#ifdef _cplusplusextern "C"{#endifvoid log4cpp_debug(const char *msg, ...);#ifdef _cplusplus}#endif#ifdef _cplusplusextern "C"{#endifvoid log4cpp_notice(const char *msg, ...);#ifdef _cplusplus}#endif#ifdef _cplusplusextern "C"{#endifvoid log4cpp_warn(const char *msg, ...);#ifdef _cplusplus}#endif#ifdef _cplusplusextern "C"{#endifvoid log4cpp_error(const char *msg, ...);#ifdef _cplusplus}#endif#ifdef _cplusplusextern "C"{#endifvoid log4cpp_crit(const char *msg, ...);#ifdef _cplusplus}#endif#ifdef _cplusplusextern "C"{#endifvoid log4cpp_alert(const char *msg, ...);#ifdef _cplusplus}#endif#ifdef _cplusplusextern "C"{#endifvoid log4cpp_emerg(const char *msg, ...);#ifdef _cplusplus}#endif#ifdef _cplusplusextern "C"{#endifvoid log4cpp_fatal(const char *msg, ...);#ifdef _cplusplus}#endif

 

Log4cppUtil.cpp

 

 

#ifndef _cplusplus#define _cplusplus#endif #include "Log4cppBase.h"#include "Log4cppUtil.h"void log4cpp_info(const char* msg, ...){Log4cppBase * instance = Log4cppBase::getInstance();va_list va;va_start(va, msg);instance->info(instance->vform(msg,va));va_end(va);}void log4cpp_debug(const char* msg, ...){Log4cppBase * instance = Log4cppBase::getInstance();va_list va;va_start(va, msg);instance->debug(instance->vform(msg,va));va_end(va);}void log4cpp_notice(const char* msg, ...){Log4cppBase * instance = Log4cppBase::getInstance();va_list va;va_start(va, msg);instance->notice(instance->vform(msg,va));va_end(va);}void log4cpp_warn(const char* msg, ...){Log4cppBase * instance = Log4cppBase::getInstance();va_list va;va_start(va, msg);instance->warn(instance->vform(msg,va));va_end(va);}void log4cpp_error(const char* msg, ...){Log4cppBase * instance = Log4cppBase::getInstance();va_list va;va_start(va, msg);instance->error(instance->vform(msg,va));va_end(va);}void log4cpp_crit(const char* msg, ...){Log4cppBase * instance = Log4cppBase::getInstance();va_list va;va_start(va, msg);instance->crit(instance->vform(msg,va));va_end(va);}void log4cpp_alert(const char* msg, ...){Log4cppBase * instance = Log4cppBase::getInstance();va_list va;va_start(va, msg);instance->alert(instance->vform(msg,va));va_end(va);}void log4cpp_emerg(const char* msg, ...){Log4cppBase * instance = Log4cppBase::getInstance();va_list va;va_start(va, msg);instance->emerg(instance->vform(msg,va));va_end(va);}void log4cpp_fatal(const char* msg, ...){Log4cppBase * instance = Log4cppBase::getInstance();va_list va;va_start(va, msg);instance->fatal(instance->vform(msg,va));va_end(va);}

 

然后再在自己的C代码中调用这个Log4cppUtil，我用的测试代码test.c如下：

 

 

#include <stdio.h>#include "Log4cppUtil.h"extern void log4cpp_info(const char *msg, ...);extern void log4cpp_debug(const char *msg, ...);extern void log4cpp_notice(const char *msg, ...);extern void log4cpp_warn(const char *msg, ...);extern void log4cpp_error(const char *msg, ...);extern void log4cpp_crit(const char *msg, ...);extern void log4cpp_alert(const char *msg, ...);extern void log4cpp_emerg(const char *msg, ...);extern void log4cpp_fatal(const char *msg, ...);int main(){int i = 3;log4cpp_info("hello: %d", i);log4cpp_debug("hello: %d", i);log4cpp_notice("hello: %d", i);log4cpp_warn("hello: %d", i);log4cpp_error("hello: %d", i);log4cpp_crit("hello: %d", i);log4cpp_alert("hello: %d", i);log4cpp_emerg("hello: %d", i);log4cpp_fatal("hello: %d", i);return 0;}

 

在C代码中要用extern告诉编译器，这个函数在其他文件

 

在Linux命令行编译如下：

 

1、编译Log4cppBase,由于我在本机上已经安装Log4cpp的库到了/use/lib下，所以可以不用置顶库的路径，直接按下面代码编译

g++ -fpic -llog4cpp -shared -g -o liblog4cppbase.so Log4cppBase.cpp

 

2、编译Log4cppUtil，由于Log4cppUtil需要用到Log4cppBase，因此需要置顶库的搜索路径为当前路径./

 

g++ -fpic -shared -g -o liblog4cpputil.so Log4cppUtil.cpp -I ./

 

3、编译自己写的test.c，生成可执行文件，在此需要把上面编译的两个库文件全部加进去，编译成可执行文件

gcc -o test test.c ./liblog4cpputil.so ./liblog4cppbase.so

编译成功！晚上赏自己个鸡腿吃！

 

 

以上是在PC机子上的编译

 

 

交叉编译进板子的话按上面那个方法是行不通的，因为系统找不到Log4cpp的库或者其他库等，可以参考前面我转载的一篇文章《【开发工具面】GCC命令行详解》，而我是把log4cpp交叉编译到/use/local下面去，而我自己的/usr下面也有一个PC版本的log4cpp，因此要注意调用哪一个命令，因此使用绝对路径/usr/local/bin/log4cpp-config

重新修改命令，如下：

 

arm-linux-g++ -fpic -shared `/usr/local/bin/log4cpp-config --libs --cflags` -o liblog4cppbase.so Log4cppBase.cpp

arm-linux-g++ -fpic -shared `/usr/local/bin/log4cpp-config --libs --cflags` -o liblog4cpputil.so Log4cppUtil.cpp -I./

arm-linux-gcc `/usr/local/bin/log4cpp-config --libs --cflags` -o test test.c log4cpp/liblog4cppbase.so log4cpp/liblog4cpputil.so

 

 

编译成功，移植到开发板上去，成功跑起来！