Hi,

Is it valid to have structure variable declartion inside compiler flag in C.
For exnample ENABLE_IPV6 is compiler option
struct {
int a;
#ifdef ENABLE_IPV6
char *ipv6;
#endif
}ipv6;

I don't know, but that looks to defeat itself. checking for a define of same within it before its valid.

It is valid (you could as well try it), but some terms should be corrected:
ENABLE_IPV6 is a 'preprocessor symbol', not a 'compiler option'
'char *ipv6;' is a 'structure-member definition, not a 'variable definition'
(Also it is really unclear what this structure is supposed to represent.)

2 members found this post helpful.

As NevemTeve says, it is entirely legal.

Assuming you have already tried that code to verify that, by the way?

I have seen this in code which is supposed to be compiled for both Linux as well as Windows.

Without looking it up, there's a primary #define like _WIN32_, or something like that, which is defined when compiling for Windows.

Certain code requires certain variable types which are specific to Windows versus how you'd declare them otherwise.

An example is something like a socket descriptor in Linux is merely an int, but for Windows, again not looking it up, it might be like WINSOCK.

Sorry for not being precise with the #define names, it's been a while.

That seems to be the most common code use for something like that, which I've seen in the past.

Hi,
Its causing random crash when i am using this strucutre in another source file.Isit due to preporocessoring is hapening first in source file then in header file?
Source code where i am using this structure is also under preporocessor directive.

1 members found this post helpful.

Crashes, by my definition occur in code when you try to run it. But you could have a different meaning.

A point I'd like to clarify here would be:

1. Is the code compiling, and this crash is when you try to run?
2. Or is the code failing to compile, and your complaint is about that?

If (a) is the situation, then Nevemteve's link shows you information about the debugger. Also there are some links in my signature for blogs about the same topic.

If (b) is the situation, then perhaps you can post the compile errors here.

Hi,

Its a crash that means runtime error not compiler error.

Have you debugged it?

Yes,Its random places it is crashing so whether if we use compiler flag in structure it will cause some issues?

You have already been asked to debug (gdb) your program. Also Electric Fence might be useful, as your problem might very well related with malloc'ed memory.
https://en.m.wikipedia.org/wiki/Electric_Fence

1 members found this post helpful.

Its not related to malloc or calloc.It seems compiler optmization creating problem when structure variable declartion were put in compoler flag

How do you know that?

How do you know that?

You have not provided any details at all about the problem, but simply insist it is a preprocessor or compilet related problem, but without giving any useful information that would help others understand the problem.

Please use the links provided above to debug the program and learn what is really happening.

Please review the Site FAQ for guidance in posting your questions and general forum usage. Especially, read the link in that page, How To Ask Questions The Smart Way. The more effort you put into understanding your problem and framing your questions, the better others can help!

1 members found this post helpful.

I remove all malloc calloc in that code even pointer also.But when i put compiler option it is rashing and in other case it is not.
Strucutre declariion is present in header file and that header file included in muliple source files.
Source files also have macro to use those strcutre variable.

Well, you have a bug (most likely numerous bugs) in your program. That cannot be solved without seeing the code. Problem is your code is way too big to simply insert here, so I suggest creating an mcve. https://stackoverflow.com/help/mcve
(Or just compress your source into a .tgz file and attach as file).

2 members found this post helpful.