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Jun 11th, 2009

Array question

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Hello.,
Have a question about array being set from function argument. I wrote this little program, and want to know why cant i set an array size from the function argument. Any help would be greatly appreciated.

C Syntax (Toggle Plain Text)
int money(int deposit, ...){
  int 
      i,
      sum = 0,
      nextvar;
      // myArr[deposit]; // < -- in here i cant set the array size from function receiving argument? and why?
  va_list 
      parg;
  va_start(parg, deposit);
  for(i=0;i<deposit;i++){
    nextvar=va_arg(parg, int);
   // myArr[i]=nextvar;
    sum+=nextvar;
  }
  va_end(parg);
  return sum/deposit;
}
int main(void){
  printf("%d", money(4,4,4,4,4));
  getchar();
  return 0;
}
int money(int deposit, ...){
  int 
      i,
      sum = 0,
      nextvar;
      // myArr[deposit]; // < -- in here i cant set the array size from function receiving argument? and why?
  va_list 
      parg;
  va_start(parg, deposit);
  for(i=0;i<deposit;i++){
    nextvar=va_arg(parg, int);
   // myArr[i]=nextvar;
    sum+=nextvar;
  }
  va_end(parg);
  return sum/deposit;
}
int main(void){
  printf("%d", money(4,4,4,4,4));
  getchar();
  return 0;
}

---
Andre Granovsky

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atman

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Jun 11th, 2009

Re: Array question

http://c-faq.com/aryptr/dynarray.html

Dave Sinkula

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long time no c

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Jun 12th, 2009

Re: Array question

short answer: static arrays are allocated when the function is called, at which point your variable is undefined. so the construct is illegal.

if you want to dynamically allocate arrays, you need to use malloc() along with a corresponding free()

jephthah

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Posting Maven

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Jun 12th, 2009

Re: Array question

>short answer: static arrays are allocated when the function is called...
Short remark: static arrays are allocated before the first call of the function. However no static arrays in OP snippet. Please, be more thoroughs in terms using.

ArkM

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Postaholic

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Jun 12th, 2009

Re: Array question

uh, yeah, i meant to say that the memory is allocated when the "program" is called.

but look if you want to be a pedant, then it's true there's no static array in the OP's snippet. what there is is an illegal attempt to use an undefined variable in what would otherwise have been a static array.

jephthah

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Jun 12th, 2009

Re: Array question

>...if you want to be a pedant...
To make distinctions between static, automatic and dynamic attributes - is it too pedantic for you?

ArkM

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Postaholic

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Jun 12th, 2009

Re: Array question

>static arrays are ............
You meant to say "fixed-length" arrays, right?

OP>in here i cant set the array size from function receiving argument? and why?
Because, array size should be a compile time constant, that is: the array size should be known at the compile time. You are already been told what is the solution by Dave.

siddhant3s

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