Undefined symbol X..:(

[Hemanth022]

I compiled this program in turbo c., it gave me error like undefined symbol 'x'., i thought it is a linker error., is it?

#define X (4+Y)
#define Y (4+X)
void main()
{
printf("%d",4*X+2);
getchar();
}

[donbock]

What is your question?
What are you trying to accomplish?

[weaknessforcats]

I think youo need to code:

#define X 4+Y
 

Using () with a macro is interpreted as providing arguments to the macro.

[Rabbit]

Doesn't that code create a circular reference?

[weaknessforcats]

Yes it does. I didn't see that. Y will be undefined trying to define X.

I never use these things.

[donbock]

I ask again ... what do you wish to accomplish?

The pair of macro definitions appear designed to provoke an infinite regress of macro expansions. Why would you want to do that? As it happens, the C Standard won't let you.

From the C99 Standard (ISO/IEC 9899) ...

6.10.3.4 Rescanning and further replacement

1 After all parameters in the replacement list have been substituted and # and ## processing has taken place, all placemarker preprocessing tokens are removed. Then, the resulting preprocessing token sequence is rescanned, along with all subsequent preprocessing tokens of the source file, for more macro names to replace.

2 If the name of the macro being replaced is found during this scan of the replacement list (not including the rest of the source file's preprocessing tokens), it is not replaced. Furthermore, if any nested replacements encounter the name of the macro being replaced, it is not replaced. These nonreplaced macro name preprocessing tokens are no longer available for further replacement even if they are later (re)examined in contexts in which that macro name preprocessing token would otherwise have been replaced.

Consider this line from your program:

printf("%d",4*X+2);

"X" is recognized as a macro name. The line becomes this after replacement of X:

printf("%d",4*(4+Y)+2);

"Y" is recognized as a macro name. The line becomes this after replacement of Y:

printf("%d",4*(4+(4+X))+2);

That's the end of the line because paragraph 2 above prevents "X" from being recognized as a macro name again. Since this last "X" isn't a macro name it must be a variable name, but your program has no variable named X so you get an undefined symbol error.

By the way, the whitespace in the #defines between the macro names and the left parentheses prevent these from being considered function-like macros.