Including line number and filename in a string variable

Question

Is there an easy way to build a string which includes the _FILE_ and _LINE_ values?

I could do something like:

std::stringstream ss;
ss << "Error in "<<_FILE_<<":"<<_LINE_<<" - too many bees!";
log(ss.str());

But that is a PITA, compared to the ideal which might be:

log("Error in "+_FILE_+":"+_LINE_+" - too many bees!");

Is there a neat way to do this in C++/STL/boost? Note I am limited to older compiler, no C++11!

http://stackoverflow.com/questions/19343205/c-concatenating-file-and-line-macros — Alex F, Oct 16 '13 at 10:42
I see questions with single and double underscores, also `_line` - do all versions exist or are people just lazy when typing? — Mr. Boy, Oct 16 '13 at 10:43
@AlexFarber same basic question but no full answer (working code example is provided) If someone provides one to either question that would be ideal. — Mr. Boy, Oct 16 '13 at 10:45
Mostly, people macroize their log calls to make this easy by baking in the boilerplate. — mah, Oct 16 '13 at 10:48
@John which part of the log message do you need to be customizable? I doubt you want to keep typing `__FILE__` and `__LINE__` everytime you want to log something. — greatwolf, Oct 16 '13 at 10:50
@AlexFarber I didn't believe I could use `+` to build a string in-place this way? — Mr. Boy, Oct 16 '13 at 10:57

score 2 · Accepted Answer · answered Oct 16 '13 at 10:57

2

As Alex commented: double macro expansion to make __LINE__ into a string and let the compiler concatenate the strings for you:

#define S(x) #x
#define S_(x) S(x)
#define S__LINE__ S_(__LINE__)

log("Error in "__FILE__":"S__LINE__" - too many bees!");

to reduce typing, as greatwolf suggested:

#define logfl(s) log("Error in "__FILE__":"S__LINE__" - "s)

logfl("too many bees!");

answered Oct 16 '13 at 10:57

mark

1

I also find it quite useful to #define log to some function returning ostream&, then you can log all kind of objects there – Peter K Oct 16 '13 at 11:26

1 Answers1