Thread: conflict in FILE and stdio

Thanks Mats,

Originally Posted by matsp

Exactly my point. There are several macro definitions that are used by gcc's header files that make it very difficult to find the actual name used. The whole thing is quite convoluted, and that is because the GCC header files are intended to work with many different versions of gcc, different OS's and different C-libraries, each of which may be slightly different in the way things need to be defined.

--
Mats

Do you know why

#define __FILE something
typedef struct _IO_FILE __FILE

works, but

typedef struct _IO_FILE __FILE
#define __FILE something

Does not work?


regards,
George

You could also use gcc options to output all the macros define in your code. In fact, you can do quite a lot of stuff...

Code:

gcc -E -o ListDef -dM -P YourSrcCode.c

will generate a list of `#define' directives for all the macros defined during the execution of the preprocessor, including predefined macros. You might not find __FILE in here because, from what i saw from the result of

Code:

gcc -E -o ListDef -dD -P YourSrcCode.c

well, __FILE is used in a type definition and used one or two lines after that. So, having a macro expansion for __FILE as something else than a type will result in an error here.

Note that i'm a poor Windows user (yeah, i'll have to install one of those Linux distribution one day heh), thus i don't have a really young version of gcc (3.4.4).

But you may be able to investigate further using the gcc options controlling the preprocessor.

If you have the latest version of gcc, you'll find here some lovely informations.

Thanks foxman,

Originally Posted by foxman

You could also use gcc options to output all the macros define in your code. In fact, you can do quite a lot of stuff...

Code:

gcc -E -o ListDef -dM -P YourSrcCode.c

will generate a list of `#define' directives for all the macros defined during the execution of the preprocessor, including predefined macros. You might not find __FILE in here because, from what i saw from the result of

Code:

gcc -E -o ListDef -dD -P YourSrcCode.c

well, __FILE is used in a type definition and used one or two lines after that. So, having a macro expansion for __FILE as something else than a type will result in an error here.

Note that i'm a poor Windows user (yeah, i'll have to install one of those Linux distribution one day heh), thus i don't have a really young version of gcc (3.4.4).

But you may be able to investigate further using the gcc options controlling the preprocessor.

If you have the latest version of gcc, you'll find here some lovely informations.

What is the differences between #define and typedef in internal operation of compiler? I find redefine a typedef type is error, but re-typedef a typedef type is ok.


regards,
George

Thanks Mats,

Originally Posted by matsp

Foxman has the solution, assuming you are able to read that output.

I would, however, recommend that you just write it down as "One of those things".

--
Mats

I agree with all of your guys' reply. I am interested to learn what is the differences between #define and typedef. Could you see my last post? Any ideas?


regards,
George

Guess you have to understand one thing. The compiler never sees any #define's. All the #define'd symbols have already been replaced by the preprocessor before the compiler sees the code.
Kurt

Thanks Mats,

Originally Posted by matsp

typedef tells the compiler "This is a new name for the type I've just given", e.g. "typedef int blah;" makes the type blah a valid use for everywhere you can use int.

#define is a "text replacement" mechanism. "#define blah int" will replace every place that uses blah into int BEFORE the actual compile takes place. This is called the "preprocessor stage". The preprocessor will take the source file, combine it with any includes into one large file, and as part of that process, replace any #define stuff. [And sort out any #if/#ifdef/#else/#endif sections by removing anything that is "false".].

Sasy now we do:

Code:

#define blah int
typedef int blah;

This will compile as:

Code:

typedef int int;

Which is probably not a good thing to do.


--
Mats

I think #define only affects the code after it, and no impact to code before it. So, it is important where (order and sequence) #define is used, and if used in different places, there will be different effect, right?


regards,
George

Thanks foxman,

Originally Posted by foxman

Code:

gcc -E -o ListDef -dM -P YourSrcCode.c

Code:

gcc -E -o ListDef -dD -P YourSrcCode.c

I have tried the above two commands. And they generate a lot of information in ListDef, several hundred lines. :-)

Could you tell me what is the function of gcc -E -o ListDef -dM -P and gcc -E -o ListDef -dD -P please?


regards,
George