Invalid characters in C preprocessors/macros? [duplicate]

Macro names should only consist of alphanumeric characters and underscores, i.e. 'a-z', 'A-Z', '0-9', and '_', and the first character should not be a digit. Some preprocessors also permit the dollar sign character '$', but you shouldn't use it.

Also have look on this... What are the valid characters for macro names?

It seems that #define TE$T 8 is working, so $ is valid.

That's not true. $ is NOT a valid character for identifiers in standard C. Some compilers, e.g, GCC , allows $ in identifiers as an extension. (See Dollar Signs)

So you are asking the wrong question, there's nothing special for names in macros, all the preprocessor does is text replacement.

Consider somefille.c

#include<stdio.h> #define NAM$ "SomeName" int main(void) { printf("Name - %s\n",NAM$); return 0; } 

Compiling the above with

gcc -pedantic somefille.c -o somefille 

gives you

somefille.c:2:9: warning: '$' in identifier or number [enabled by default] #define NAM$ "SomeName" 

This [ page ] says.

-pedantic
Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that use forbidden extensions, and some other programs that do not follow ISO C and ISO C++. For ISO C, follows the version of the ISO C standard specified by any -std option used.

As per the strict standard the macro name must have no spaces in it, and it must conform to the same naming rules that C variables follow: Only letters, digits, and the underscore ( _ ) character can be used, and the first character cannot be a digit.

The problem is that various compilers do not comply with this. An example is gcc which I mentioned above.

Having said that, below rules are still obeyed:

1. A macro name must not begin with a number, if you violate this you may get an error like :

   error: macro names must be identifiers 

2. A macro name must not contain spaces. For instance #define FULL NAME "Your name" gives you :

   error: ‘NAME’ undeclared (first use in this function)