allocation and freeing of an array of ints

first of all, how come you can do this in C++ and not in C

int a[n];

secondly, why is the array "a" being printed after i freed it in the following piece of code:

int *a = new int[10];
for (int i = 0; i < 10; ++i)
a[i] = i + 1;

delete [] a;

for (int i = 0; i < 10; ++i)
cout << a[i] << " ";

kind regards

Quote:

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Originally Posted by boxden

first of all, how come you can do this in C++ and not in C

int a[n];

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Unless n is a constant positive integer, you cannot do that in C++, but under certain circumstances you can do that in C even if n is not a constant, with respect to the 1999 edition of the C standard (this is the variable length array feature).

If you are able to use variable length arrays in C++, then you are relying on your compiler's language extension.

Quote:

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Originally Posted by boxden

secondly, why is the array "a" being printed after i freed it in the following piece of code:

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Undefined behaviour. You should not be accessing that destroyed array.

>first of all, how come you can do this in C++ and not in C
>
>int a[n];

The feature you're using there is actually a C99 feature that's not available in C++ unless you use non-standard compiler extensions.

thank you for the reply guys, i was compiling it like this
g++ *.cpp

what flags do i need to set to have the same behavior as C's gcc -ansi -Wall -pedantic?

also laserlight, could you tell me more about C's possibility of using int n[var]? I thought ansi C prohibited it?

thanks in advance

Quote:

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Originally Posted by boxden

thank you for the reply guys, i was compiling it like this
g++ *.cpp

what flags do i need to set to have the same behavior as C's gcc -ansi -Wall -pedantic?

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Use -Wall and -pedantic too :)

Quote:

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Originally Posted by boxden

also laserlight, could you tell me more about C's possibility of using int n[var]? I thought ansi C prohibited it?

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You might want to search the Web, e.g., The New C: Why Variable Length Arrays?