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The accepted answer to the question C++ concatenating __FILE__ and __LINE__ macros? work for FILE and LINE, but I would like to add the func macro too.

#define S1(x) #x
#define S2(x) S1(x)
#define S3(x) x

#define LOCATION __FILE__ " : " S3(__func__) " : " S2(__LINE__)

this gives error

log.cpp|15 col 15 error| note: in definition of macro ‘S3’

Also tried,

#define LOCATION __FILE__ " : " __func__ " : " S2(__LINE__)

gives error 

log.cpp|30 col 9 error| note: in expansion of macro ‘LOCATION’

I understand that LINE was a integer hence needed #x, but func is a char array. How do I get this working? Any help?

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mtk
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2 Answers2

2

As cpplearner mentioned correctly __func__ is not a macro, it's a special function-local predefined variable. I achieved desired result by

#define S1(x) #x
#define S2(x) S1(x)
#define LOCATION string(__func__) + " : " S2(__LINE__) + " : "

and I use it by sending the string to a wrapper log function

void log(string s) {
     cout << s <<endl;
}

void abc(){
    log(LOCATION + string("some message "));
}

Outputs:

abc : 23 : some message
mtk
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__func__ is a variable (not a macro unlike __FILE__ or __LINE__)

This related question Treating __func__ as a string literal instead of a predefined identifier has good explanation.

Ajay Gaonkar
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