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Multiple function definition #define

I have a logger.h file and a macro function definition for logging:

//logger.h:
#ifndef _LOGGER_H_
#define _LOGGER_H_

#ifdef LOG_DEBUG
    ofstream debug_log("debug.log");
    #define log(...) debug_log << __FILE__ << ":" << __PRETTY_FUNCTION__ << ":" << __LINE__ << "| " << __VA_ARGS__ << std::endl
#else
    #define log(...)
#endif

#endif

This header file is included in several c. and using the log () function. g ++ gives:

/tmp/ccMAjYSm.o:(.bss+0x0): multiple definition of `debug_log'
/tmp/ccHj3w7u.o:(.bss+0x0): first defined here
/tmp/cc3LQ9GQ.o:(.bss+0x0): multiple definition of `debug_log'
/tmp/ccHj3w7u.o:(.bss+0x0): first defined here

Any hint?

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2 answers


If you have declared LOG_DEBUG

at the project level (or in multiple translation units) they will all see

ofstream debug_log("debug.log");

and you will have multiple definitions.

Possible solution: put it in a single translation unit, showing everyone else information about its existence



Heading

#ifndef _LOGGER_H_
#define _LOGGER_H_

#ifdef LOG_DEBUG
    extern ofstream debug_log;
    #define log(...) debug_log << __FILE__ << ":" << __PRETTY_FUNCTION__ << ":" << __LINE__ << "| " << __VA_ARGS__ << std::endl
#else
    #define log(...)
#endif

#endif

Cpp file

ofstream debug_log("debug.log");
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Every source file that ends up #include

logger.h will see this:

ofstream debug_log("debug.log");


and thus create this object. You now have several objects named debug_log

.

Go ahead and declare the object here, but put it in the .cpp file.

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