New/delete vs malloc/free

This is a discussion on New/delete vs malloc/free within the C++ Programming forums, part of the General Programming Boards category; I have used C up to now, just starting to teach myself C++. Are there any advantages to using new/delete ...

  1. #1
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    New/delete vs malloc/free

    I have used C up to now, just starting to teach myself C++. Are there any advantages to using new/delete over malloc/free besides less typing?

    Are they essentially the same thing, just with different syntaxes?

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    You mean aside from the fact that new/delete calls the constructor/destructor for the objects it creates, which malloc/free doesn't. Sure, beside that fact, they are pretty much the same. They both allocate memory and assign it to the pointer you give, and release the memory from a given pointer.

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  3. #3
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    They are very different in that malloc/free just gives you a bunch of bytes, whereas new/delete construct and destruct allocated objects. That is, you can't use malloc/free for anything that needs to have its constructor/destructor called (unless you want to go through great trouble).

    Furthermore, in C++ it is almost always possible to avoid the array form of new[]/delete[], since you can just use std::vector. It is also possible to avoid explicit calls to delete, if you let smart pointers like boost::shared_ptr take care of new'ed objects.
    I might be wrong.

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    I guess I should have been more specific - I am interested in arrays of basic types: for example

    is

    Code:
    array = new int[10]
    functionally the same as

    Code:
    array = (int *) malloc(10 * sizeof(int))
    ?

  5. #5
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    Not quite. If malloc was unable to allocate memory, it would return a null pointer, but the corresponding behaviour from new[] would be to throw std::bad_alloc.
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    Quote Originally Posted by KBriggs View Post
    I guess I should have been more specific - I am interested in arrays of basic types: for example

    is

    Code:
    array = new int[10]
    functionally the same as

    Code:
    array = (int *) malloc(10 * sizeof(int))
    ?
    As Laserlight points out, new and malloc behaves differently when there isn't enough memory to satisfy the request. However, the other part of the question is sort of "what should I use", which I would say is:
    1. If you are writing C, you haven't got a choice: malloc/free it is.
    2. If you are writing C++, use new/delete - it will should never be wrong to do this, and if for some reason you change your mind, and decide to change the array of integers into a class CInteger, you do not need to make as many changes.

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  7. #7
    C++まいる!Cをこわせ! Elysia's Avatar
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    There is also more type-safety.
    This is legal (but wrong) in C:
    float* x = malloc(sizeof(int));
    On the contrary, if you do it in C++, you will get a compile error:
    float* x = new int;

    Type-safety is one of C++'s most powerful features. Make good use of it.
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    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.

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