Pointers to structures

This is a discussion on Pointers to structures within the C Programming forums, part of the General Programming Boards category; i got the following: Code: typedef struct { int n, d; } frac; int main(void) { frac *f1; f1 = ...

  1. #1
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    Question Pointers to structures

    i got the following:
    Code:
    typedef struct {
      int n, d;
    } frac;
    int main(void) {
      frac *f1;
      f1 = (frac *) malloc(sizeof(frac));
    I am a bit confused with the malloc. Why do you have to do this, (frac *) , before it??

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    You don't. In fact, you shouldn't.

    (If your compiler is telling you you should, that's because you're using a C++ compiler.)

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    Frequently Quite Prolix dwks's Avatar
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    (If your compiler is telling you you should, that's because you're using a C++ compiler.)
    Or perhaps you forgot to #include <stdlib.h>.
    dwk

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    Banned master5001's Avatar
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    Quote Originally Posted by dwks View Post
    Or perhaps you forgot to #include <stdlib.h>.
    Even that is questionable since most modern compilers will implicitly accept malloc() without including stdlib.h. Though I applaud dwks for being so thorough and proper

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    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by tabstop View Post
    You don't. In fact, you shouldn't.
    Someone once told me that it did not matter if you did, because there are always tools to spot the bugs in your code.

    So to answer the question: In C, you do not have to do it. You can, but you do not have to.
    Is it good practice to do it? Debatable. I am sure many would have their own opinions.
    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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    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by Elysia View Post
    Someone once told me that it did not matter if you did, because there are always tools to spot the bugs in your code.

    So to answer the question: In C, you do not have to do it. You can, but you do not have to.
    Is it good practice to do it? Debatable. I am sure many would have their own opinions.
    Explicitly casting the return of malloc() is like saying, "I don't trust the language." The whole point (in C, not C++) of void * is that it can be silently converted to any other pointer type -- and any pointer type can silently convert to void *. Using an explicit cast is like denying this aspect of the language, and IMHO indicates a misunderstanding of the point of void * in the first place.

    Calling functions without prototypes is just wrong. Including stdlib.h isn't optional.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  8. #8
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by brewbuck View Post
    Explicitly casting the return of malloc() is like saying, "I don't trust the language." The whole point (in C, not C++) of void * is that it can be silently converted to any other pointer type -- and any pointer type can silently convert to void *. Using an explicit cast is like denying this aspect of the language, and IMHO indicates a misunderstanding of the point of void * in the first place.
    I am just saying that IMHO, since void* can be anything (as you say, any pointer type can be implicitly converted to void*), so that does not necessarily mean that void* is the type you are assigning to. Maybe it is merely my C++ background.
    That casting the return can mask the call without prototypes is just wrong and it is bad compiler, but I concede that that is not the aspect I am worried about.
    Anyhow. I am just pointing out that, no, it is not wrong to cast the return, and no, it is not wrong to not do it either. In C, it is a taste thing.

    Calling functions without prototypes is just wrong. Including stdlib.h isn't optional.
    200% agreed.
    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.

  9. #9
    Banned master5001's Avatar
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    I never once said the word "optional" I said I appreciate his use of proper coding.

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