Help: Convert C to C++

This is a discussion on Help: Convert C to C++ within the C++ Programming forums, part of the General Programming Boards category; Hello, I'm trying to convert a program from C to C++. Code: #define RANDSIZL (4) /* I recommend 8 for ...

  1. #1
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    Help: Convert C to C++

    Hello,
    I'm trying to convert a program from C to C++.
    Code:
     
    #define RANDSIZL   (4)  /* I recommend 8 for crypto, 4 for simulations */
    #define RANDSIZ    (1<<RANDSIZL)
    
    /* context of random number generator */
    struct randctx{
      int randcnt;
      int randrsl[RANDSIZ];
      int randmem[RANDSIZ];
      int randa;
      int randb;
      int randc;
    };
    
    typedef  struct randctx  randctx;
    The typedef line doesn't make sense to me. A new name (randctx) for struct randctx? If I delete the typedef line it should still compile, but it doesn't. Any idea why? What's the point of having such a typedef line?

  2. #2
    C++ Witch laserlight's Avatar
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    A new name (randctx) for struct randctx?
    Yes.

    If I delete the typedef line it should still compile, but it doesn't.
    Did you compile with a C++ compiler?

    Any idea why? What's the point of having such a typedef line?
    So that you can use the name randctx instead of struct randctx, but obviously this does not apply in C++.
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  3. #3
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    The code I posted compiles both wit h gcc and g++. The program that I'm converting won't compile (gcc) if I remove the typedef line.

    What's the easiest way to convert C to C++ if you don't know C?

  4. #4
    Cat without Hat CornedBee's Avatar
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    Compile the program as it is with a C++ compiler, and fix the errors.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  5. #5
    C++まいる!Cをこわせ!
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    It should work. Otherwise, what's the error?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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    I can't post the error cause it's too big. The program that I'm trying to convert to c++ is called Flam3.

  7. #7
    C++まいる!Cをこわせ!
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    Post a few compile errors first. Fix them. Go on to the next.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  8. #8
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    Quote Originally Posted by Arlenik View Post
    Code:
     
    /* context of random number generator */
    struct randctx{
      int randcnt;
      int randrsl[RANDSIZ];
      int randmem[RANDSIZ];
      int randa;
      int randb;
      int randc;
    };
    
    typedef  struct randctx  randctx;
    The typedef line doesn't make sense to me. A new name (randctx) for struct randctx? If I delete the typedef line it should still compile, but it doesn't. Any idea why? What's the point of having such a typedef line?
    In C, the declaration of struct randctx declares a struct tag named "randctx" and (effectively) a type named "struct randctx". The typedef makes randctx an alternative name for the type "struct randctx".

    In C++, the declaration of struct randctx implicitly also declares a type named randctx, so the typedef is not required.

    Hence you can expect the above to compile happily with a C compiler, but not with a C++ compiler (with some ambiguity in that statement depending on compatibility settings supported by some compilers).

  9. #9
    Cat without Hat CornedBee's Avatar
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    Compiles just fine even in pedantic mode. C++ was made with C compatibility in mind, and therefore has no problem with a typedef overriding the struct name.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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