Compiler error for logger with a macro

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Hi

I need help.

Macro declaration is in a header file as below.
#define LogErr(message, ...) Log(ERR, __FILE__, __FUNCTION__, __LINE__, message, ##__VA_ARGS__)

Function Definition in a .C file is as below
void Log(char* logSeverity, char* fileName, const char* functionName, int lineNo, char* message,...);

From a .C file LogErr is called twice as below. When I compile I get error for the second called with the error message "too few arguments in macro invocation"

LogErr("Ready for messages to %d %s", 6000,"Hallo6");
LogErr("Ready for messages");

How can the problem be solved?

Thanks
Merh

Posted 21-May-15 22:36pm

merh

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Frankie-C · Answer 1 · 2015-05-22T01:35:00

Solution 2

ANSI requires that the elipsis (...) declaration of a macro receives at least one parameter.
While some compilers also accepts no arguments for variable arguments (i.e. gcc) this is not true for all.
The best solution is to modify the macro in this way:

C++

#define LogErr(...) Log(ERR, __FILE__, __FUNCTION__, __LINE__, __VA_ARGS__)

Because the message parameter is alway present, satisfying the ellipsis, this solves the problem.

Posted 22-May-15 1:35am

Frankie-C

Updated 22-May-15 2:21am

v3

Comments

Andreas Gieriet 22-May-15 10:07am

My 5!
This holds for *macros* only as given in the example above. The respective C-standard text is defined in 6.10.3, paragraph 4: [...] there shall be more arguments in the invocation than there are parameters in the macro definition (excluding the ...). [...].
Cheers
Andi
PS: For *functions* with variable arguments, there may be zero arguments, though.

Frankie-C 22-May-15 11:37am

Thanks Andi

Richard MacCutchan · Answer 2 · 2015-05-21T23:32:00

Solution 1

Add a dummy parameter (NULL) after the string.

Posted 21-May-15 23:32pm

Richard MacCutchan