macros - Defining functions using backslash in c++ -

i saw people using backslash when define functions in macros as:

#define classnamenodebug(typenamestring)                                    \     static const char* typename_() { return typenamestring; }                 \     static const ::foam::word typename 

i did easy test. got bunch of errors. testing code follows: in testmacro.h file:

#define declearlarger(first,second)                                                          \     double whichislarger(double first,double second){ return (first>second) ? fisrt : second;} 

in main() function:

int second =2; int first =1;  cout << declearlarger(first,second) << endl; 

the errors are:

/home/jerry/desktop/backslash/backslash_test/testmacro.h:7: error: expected primary-expression before 'double'      double whichislarger(double first,double second){ return (first>second) ? fisrt : second;}      ^ /home/jerry/desktop/backslash/backslash_test/testmacro.h:7: error: expected ';' before 'double'      double whichislarger(double first,double second){ return (first>second) ? fisrt : second;}      ^ /home/jerry/desktop/backslash/backslash_test/main.cpp:24: error: expected primary-expression before '<<' token      cout << declearlarger(first,second) << endl;                                          ^ 

that concludes testing errors. can give suggestions why these errors pop up?

you're trying use function definition (generated macro) inside expression. c++ not allow such thing. instead define macro be

#define declearlarger(first,second) \         (((first)>(second)) ? (first) : (second)) 

and work. note none of errors come backslash, generated because of function definition/expression clash.