Question

I trying to incorporate a simple error logging into my existing app, at the moment it reports errors just using cout so I was hoping to keep a similar interface using the << operator. However I want it to log the line and function the error occurred, but I don’t want to have to type __LINE__, __FUNCTION__ every time I need to log. Does anyone know a trick I can use to allow the __LINE__ macro to be used inside another function, reporting the calling line instead? Hope that makes sense.

class myLogClass {     uint8_t level;                   public:                      bool operator<<( const char * input );           };  bool myLogClass::operator<<( const char * input ) {     logItInSQL( input );     return true; } 

Instead of this every time

myLogClass << 'Line No: ' << __LINE__     << ' Function: ' << __FUNCTION__     << ' Error: ' << 'This is my error to be logged'; 

I would like to just be able to do:

myLogClass << 'This is my error to be logged';  bool myLogClass::operator<<( const char * input ) {     logItInSQL( ' Line No: __LINE__' );     logItInSQL( ' Function: __FUNCTION__' );     logItInSQL( ' Error: ' + input );     return true; } 

Answer 1

myLogClass << 'Line No: ' << __LINE__ ... 

With your operator << chaining will not work since it returns a bool.

bool myLogClass::operator << (const char * input) 

It is customary to define stream insertion as follows:

std::ostream& myLogClass::operator << (std::ostream& o, const char * input) {     // do something     return o; } 

Do this:

#define log(o, s) o << 'Line No: ' << __LINE__ << \                    ' Function: ' << __FUNCTION__ << \                    ' Error: ' << s // note I leave ; out 

Additionally, you can wrap the macro in a do-while loop:

#define log(o, s) do { o << 'Line No: ' << __LINE__ << \                    ' Function: ' << __FUNCTION__ << \                    ' Error: ' << s; \                    } while(0) // here, I leave ; out 

Then you can happily write:

 myLogClass myLogger; // do this   // use it log(myLogger, 'This is my error to be logged'); // note the ;