Thread: macro concatenation question

  1. #1
    Registered User
    Join Date
    May 2011

    macro concatenation question


    I have the following code in my application:

    #define PORT 1234
    #define HOST ""
    Because the 1234 value appears in both definitions, I tried to concatenate the PORT to the HOST, so it would look like this:

    #define PORT 1234
    #define HOST "" PORT
    When I try to compile the code everywhere where I used the HOST macro in some way the compiler gives me the following error:

    "error: expected ) before numeric constant"

    I guess this is because the PORT macro is an integer, the second is string, and when the compiler concatenates the two of them, converts the second macro to integer too.

    Can somebody tell me, how can I get rid of this problem?

    P.s.: If I define the PORT as string (#define PORT "1234") it is ok, but I would like to keep it integer.

    Thank you.

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    Like so
    #include <stdio.h>
    #define PORT 1234
    #define MKSTR(x)    #x
    #define MKSTR2(x)   MKSTR(x)
    #define HOST "" MKSTR2(PORT)
    int main()
      return 0;
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
    Registered User
    Join Date
    May 2011
    Thank you.

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