What's the usage?

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  • ikl
    #1

    What's the usage?

    What's the usage of #ifdef and #endif in the code below?

    #ifdef C_DEF
    class C
    {
    public:
    void Repair();
    };

    void C::Repair () {
    ....
    }
    #endif

    Since I understand using like:

    #ifdef C_DEF
    class C
    {
    public:
    void Repair();
    };
    #endif

    void C::Repair () {
    ....
    }


    Thanks!


    Tags: None
    • Mike Wahler
      #2
      Re: What's the usage?


      "ikl" <ikl72@dsp.co m> wrote in message
      news:PMscc.2606 7$vo5.826762@bg tnsc05-news.ops.worldn et.att.net...[color=blue]
      > What's the usage of #ifdef and #endif in the code below?
      >
      > #ifdef C_DEF[/color]

      if the symbol 'C_DEF' is defined (with a #define directive),
      then translate all the following code...
      [color=blue]
      > class C
      > {
      > public:
      > void Repair();
      > };
      >
      > void C::Repair () {
      > ...
      > }[/color]

      .... until a
      [color=blue]
      > #endif[/color]

      ... directive is encountered.
      [color=blue]
      >
      > Since I understand using like:
      >
      > #ifdef C_DEF
      > class C
      > {
      > public:
      > void Repair();
      > };
      > #endif[/color]

      This is the same as above, except it doesn't
      include the definition of the member function
      'Repair()'.
      [color=blue]
      >
      > void C::Repair () {[/color]

      A class 'C' must be visible at this point for
      this to be valid.
      [color=blue]
      > ...
      > }[/color]


      Look up 'preprocessor directives' in your C++ book.

      -Mike


        Comment

        • Mike Wahler
          #3
          Re: What's the usage?


          "ikl" <ikl72@dsp.co m> wrote in message
          news:PMscc.2606 7$vo5.826762@bg tnsc05-news.ops.worldn et.att.net...[color=blue]
          > What's the usage of #ifdef and #endif in the code below?
          >
          > #ifdef C_DEF[/color]

          if the symbol 'C_DEF' is defined (with a #define directive),
          then translate all the following code...
          [color=blue]
          > class C
          > {
          > public:
          > void Repair();
          > };
          >
          > void C::Repair () {
          > ...
          > }[/color]

          .... until a
          [color=blue]
          > #endif[/color]

          ... directive is encountered.
          [color=blue]
          >
          > Since I understand using like:
          >
          > #ifdef C_DEF
          > class C
          > {
          > public:
          > void Repair();
          > };
          > #endif[/color]

          This is the same as above, except it doesn't
          include the definition of the member function
          'Repair()'.
          [color=blue]
          >
          > void C::Repair () {[/color]

          A class 'C' must be visible at this point for
          this to be valid.
          [color=blue]
          > ...
          > }[/color]


          Look up 'preprocessor directives' in your C++ book.

          -Mike


            Comment

            • JaSeong Ju
              #4
              Re: What's the usage?

              #ifdef and #endif are used for conditional compilation.
              If C_DEF is defined, then compile in the class C and its
              public member functions.

              If C_DEF is not defined, then class C is
              not included. Then of course you dont want to include
              the
              void C::Repair () {
              ....
              }
              member function, since its an error.

              [color=blue]
              > What's the usage of #ifdef and #endif in the code below?
              >
              > #ifdef C_DEF
              > class C
              > {
              > public:
              > void Repair();
              > };
              >
              > void C::Repair () {
              > ...
              > }
              > #endif
              >
              > Since I understand using like:
              >
              > #ifdef C_DEF
              > class C
              > {
              > public:
              > void Repair();
              > };
              > #endif
              >
              > void C::Repair () {
              > ...
              > }
              >
              >
              > Thanks!
              >
              >[/color]

                Comment

                • JaSeong Ju
                  #5
                  Re: What's the usage?

                  #ifdef and #endif are used for conditional compilation.
                  If C_DEF is defined, then compile in the class C and its
                  public member functions.

                  If C_DEF is not defined, then class C is
                  not included. Then of course you dont want to include
                  the
                  void C::Repair () {
                  ....
                  }
                  member function, since its an error.

                  [color=blue]
                  > What's the usage of #ifdef and #endif in the code below?
                  >
                  > #ifdef C_DEF
                  > class C
                  > {
                  > public:
                  > void Repair();
                  > };
                  >
                  > void C::Repair () {
                  > ...
                  > }
                  > #endif
                  >
                  > Since I understand using like:
                  >
                  > #ifdef C_DEF
                  > class C
                  > {
                  > public:
                  > void Repair();
                  > };
                  > #endif
                  >
                  > void C::Repair () {
                  > ...
                  > }
                  >
                  >
                  > Thanks!
                  >
                  >[/color]

                    Comment

                    • Kevin Goodsell
                      #6
                      Re: What's the usage?

                      JaSeong Ju wrote:
                      <A top-posted message.>

                      Please stop top-posting. Read section 5 of the FAQ (which you should
                      have already read) for posting guidelines:

                      C++ FAQ
                      http://www.parashift.com/c++-faq-lite/


                      -Kevin
                      --
                      My email address is valid, but changes periodically.
                      To contact me please use the address from a recent posting.

                        Comment

                        • Kevin Goodsell
                          #7
                          Re: What's the usage?

                          JaSeong Ju wrote:
                          <A top-posted message.>

                          Please stop top-posting. Read section 5 of the FAQ (which you should
                          have already read) for posting guidelines:

                          C++ FAQ
                          http://www.parashift.com/c++-faq-lite/


                          -Kevin
                          --
                          My email address is valid, but changes periodically.
                          To contact me please use the address from a recent posting.

                            Comment

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