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Please Help Dynamic Memory Allocation.
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Each of the following program segments might
have syntax, logic or other kinds of errors. If there are errors,
correct, otherwise answer "no error". Assume all function headers
are correct.
Function copy_array receives an integer array a and
its size length, as parameters. It copies the array a into
another integer array b newly created, and returns the address
of the new array b.
CORRECT:
My Question is that is dynamic memory allocation really necessaryÉ since you already know the size of the array which is being passed by the caller. Also can some someone explain each step of line 1 and 2. Thanks in advance.
have syntax, logic or other kinds of errors. If there are errors,
correct, otherwise answer "no error". Assume all function headers
are correct.
Function copy_array receives an integer array a and
its size length, as parameters. It copies the array a into
another integer array b newly created, and returns the address
of the new array b.
C++ Syntax (Toggle Plain Text)
CORRECT:
int *copy_array ( int a[], int length )
{
int i;
int *b = calloc( length, sizeof(int)); line 1
/* or int *b = malloc( length * sizeof(int)); */ line 2
for (i =0; i < length; i++ )
b[i] = a[i];
return b;
/* or return &b[0] */
}My Question is that is dynamic memory allocation really necessaryÉ since you already know the size of the array which is being passed by the caller. Also can some someone explain each step of line 1 and 2. Thanks in advance.
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Join Date: Oct 2007
Posts: 62
Reputation: 
Solved Threads: 8
Junior Poster in Training
>is dynamic memory allocation really necessaryÉ since you already
>know the size of the array which is being passed by the caller
Really? How do you know? If you're talking about the length parameter, then yes, dynamic allocation really is necessary because array sizes must be compile-time constants. This isn't legal C++:
>Also can some someone explain each step of line 1 and 2.
Line 1 allocates length * sizeof(int) bytes and assigns it to b.
Line 2 allocates length * sizeof(int) bytes and assigns it to b.
Both lines are incorrect and won't compile as C++ because C++ doesn't support an implicit conversion from void*, and both calloc and malloc return void*.
>know the size of the array which is being passed by the caller
Really? How do you know? If you're talking about the length parameter, then yes, dynamic allocation really is necessary because array sizes must be compile-time constants. This isn't legal C++:
C++ Syntax (Toggle Plain Text)
Line 1 allocates length * sizeof(int) bytes and assigns it to b.
Line 2 allocates length * sizeof(int) bytes and assigns it to b.
Both lines are incorrect and won't compile as C++ because C++ doesn't support an implicit conversion from void*, and both calloc and malloc return void*.
What about in C. É
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Originally Posted by Ptolemy 
>is dynamic memory allocation really necessaryÉ since you already
>know the size of the array which is being passed by the caller
Really? How do you know? If you're talking about the length parameter, then yes, dynamic allocation really is necessary because array sizes must be compile-time constants. This isn't legal C++:
>Also can some someone explain each step of line 1 and 2.C++ Syntax (Toggle Plain Text)
Line 1 allocates length * sizeof(int) bytes and assigns it to b.
Line 2 allocates length * sizeof(int) bytes and assigns it to b.
Both lines are incorrect and won't compile as C++ because C++ doesn't support an implicit conversion from void*, and both calloc and malloc return void*.
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Join Date: Aug 2005
Posts: 15,445
Reputation: 
Solved Threads: 1475
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Originally Posted by warpstar
What about in C. É
>> because array sizes must be compile-time constants
Not any more -- C99 has changed that for C language, not sure if it will also apply to C++ or not.
Last edited by Ancient Dragon; Oct 25th, 2007 at 6:51 pm.
Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.
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