Thread: Preprocessor fight

I have the following sample from my code....

Code:

#include <stdio.h>
#define D \
#define
#define CMD(name,code) D CMD_##name #code" "#name

CMD(    ACK,    069)
CMD(    CLOSE,  255)
CMD(    HELP,   131)
CMD(    IDENT,  099)

int main()
{
    printf("%s", CMD_HELP);
}

But when i try to compile the files using the #defined strings, i get the error:

test.c:7: error: stray ‘#’ in program

Is there a workaround? I know #define #define is generally not very common, but is possible and i would to know how to correctly use such a construction if it is not too much to ask, oh great masters...

You can't #define a #define.

I forget what the one-pass version is, but I've generally done this.

Yes that's great abuse of the preprocessor, but preprocessing my header file is done with no problem, except from the fact that the #define statements generated have an extra space before them which i can't remove so far...

After preprocessing your file looks like this:

Code:

 #define CMD_ACK "069"" ""ACK"
 #define CMD_CLOSE "255"" ""CLOSE"
 #define CMD_HELP "131"" ""HELP"
 #define CMD_IDENT "099"" ""IDENT"

int main()
{
    printf("%s", CMD_HELP);
}

Unfortunately, now it seems it is the compilers turn, and #defines are not what it expects to see in the preprocessed file.

I know, i kept my original idea as a backup, and sed'ed the preprocessed out of gcc to make my final header file. It works fine now.

>> #define D \ // can't use meta characters in a define.
#define // *something*
#define CMD(name,code) D CMD_##name #code" "#name // ??
cout << CMD( foo, bar ) << endl; // error: expected ';' before CMD_foo

that's all just syntactically incorrect. what are you trying to do?

So you are alive after all... Had sent you a pm about your signature.
What i am trying to do, is use the preprocessor to create a lot of statements of the form:

Code:

#define CMD_ACK         "042 ACK"
#define CMD_CLOSE     "255 CLOSE"
...

and avoid the retyping of the words define and the CMD_xxx suffix.