Better than recursing on main - for Mephisto

[Mephisto]

Arta, do you get that error when you try to declare an array with a non-constant value/expression?

[dxoigmn]

I thought you could only use a constant value/expression when declaring arrays...

Perhaps argc/argv are special?  I have no idea why it works


Here's something else interesting that I noticed:

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int main()
{
       main();
       return 0;
}

This will not compile on Linux.  I get the error:

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iago@laptop:~/Projects/C$ gcc -Wall test2.cpp
/tmp/cc8BvbGZ.o(.eh_frame+0x11): undefined reference to `__gxx_personality_v0'
collect2: ld returned 1 exit status
iago@laptop:~/Projects/C$

gcc doesn't like *.cpp files.  You need to use g++ or rename test2.cpp to test2.c.

[MyndFyre]

Arta, do you get that error when you try to declare an array with a non-constant value/expression?

I'm somewhat confused (perhaps due to my C newbletness), but I was under the impression that you *could* create variable-size arrays.  Vis-a-vis:

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int main()
{
  cout << "Enter a value:" << endl;
  int num = 0;
  cin >> num;

  int *array = malloc(num * sizeof(int));
  if (array == NULL)
   return 1;

  //...
}


and then you would effectively have an array with the size that you wanted.  I can't remember if it can be cast or not...  It seems like it should be able to, by setting an array pointer to the variable of the array itself.

Like I said though, I'm a C newblet, so I could be off.

[K]

C99 says you can do this:

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int x = 10;

int Foo[x];


you could do it like so:

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int x = 10;
int *Foo = malloc(x * sizeof(int));
// ...
free(Foo);


the difference is primarily that you have to free() the second, and where they are allocated.

[iago]

C99 says you can do this:

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int x = 10;

int Foo[x];


you could do it like so:

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int x = 10;
int *Foo = malloc(x * sizeof(int));
// ...
free(Foo);


the difference is primarily that you have to free() the second, and where they are allocated.

Also, you can return the second, it's on the heap, but you can't return the first one, it's on the stack and will get broken.

[Arta]

Arta, do you get that error when you try to declare an array with a non-constant value/expression?

Looks that way, yes. I get the same errors with:

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int main(int argc, char **argv)
{
   int x = 10;

   int y[x];

   return 0;
}



Perhaps there's a compiler option somewhere that controls this?

Edit: perhaps not - see ms-help://ms.vscc/MS.MSDNVS/vccore/html/C2057.htm:

expected constant expression

The context requires a constant expression. The following sample generates C2057:

// C2057.cpp
int i;
// use the line below to resolve the error
// const int i = 8;

int b;   // C2057

int main() {
}

[Mephisto]

That's what I thought.  I could've sworn you could never use a non-constant value when declaring your array, though I don't see why you couldn't, it will always know how much memory to allocate.  Perhaps some compilers now violate this?  Or the standards have changed...?