how to get FILE, func and LINE macro working in single line?

Question

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?

mtk · Accepted Answer · 2016-06-04 06:40:51Z

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

answered Jun 4, 2016 at 6:40

mtk

13.8k16 gold badges75 silver badges117 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Ajay Gaonkar · Accepted Answer · 2018-01-01 06:23:55Z

0

__func__ is a variable (not a macro unlike __FILE__ or __LINE__)

answered Jan 1, 2018 at 6:23

Ajay Gaonkar

98 bronze badges