How to get the file name and a line number of a function call?

Question

I have two functions in different source files:

a.cpp

void A()
{
    B();
}

b.cpp

void B()
{
    std::cout << "B() called from file: " << ??? << " line: " << ??? << std::endl;
}

How can I get the file name and line number of the call?

This should not be a duplicate because it's not sufficient to just use those macros, it's also necessary to "hide the function behind a macro" (see the accepted answer) And that's not the only possible answer, there's another answer in C++20 which would not be appropriate for the other question (see the comment above) — user202729, Dec 30 '19 at 03:55

score 15 · Accepted Answer · edited Jun 08 '18 at 09:10

15

In general you can do this automatically by hiding your function behind a macro call which passes allong the __FILE__ and __LINE__ values

void _B(const char* file, int line) { ... } 
#define B() _B(__FILE__, __LINE__)

This is by no means a foolproof solution though. It's possible for developers to call _B directly or for _B to be called from generated code, assembly, etc .... where there may be no meaningful file / line number

OP asked for an example with arguments

void _C(int p1, char p2, const char* file, int line) { ... } 
#define C(p1, p2) _C(p1, p2, __FILE__, __LINE__)

edited Jun 08 '18 at 09:10

Community

1
1

answered Jan 09 '14 at 14:12

JaredPar

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Did you pass file as an int on purpose? – MB-F Jan 09 '14 at 14:13
1

@kazemakase no, haven't finished coffee yet, making idiot mistakes :( – JaredPar Jan 09 '14 at 14:14
and what if the B() function would have other arguments? – Qualphey Jan 09 '14 at 14:16
@VitaliusKuchalskis add them into the macro as well and forward them onto the implementation function – JaredPar Jan 09 '14 at 14:19
and also... What about constructor macros? – Qualphey Jan 09 '14 at 16:53
@VitaliusKuchalskis not sure what you mean by that. Can you elaborate? – JaredPar Jan 09 '14 at 16:55
I mean what if the function B() is a constructor of a class B? – Qualphey Jan 09 '14 at 17:00
@VitaliusKuchalskis in that case you'd either need `_B` to return an instance of `B` or have a macro that is not the class name. Or alternative switch from constructors to static creation methods. – JaredPar Jan 09 '14 at 17:29

score 0 · Answer 2 · answered Jan 09 '14 at 14:11

0

code: printf("%s(%d)--:",__FILE__,__LINE__);

reference: http://gcc.gnu.org/onlinedocs/cpp/Standard-Predefined-Macros.html

answered Jan 09 '14 at 14:11

Jay

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I do not understand what you mean. – Ingo Jun 26 '22 at 16:23

How to get the file name and a line number of a function call?

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