Basic array allocation in function

I have a function for splitting a string.

This function returns a basic array which is allocated inside the function

The code for this function is

string mySplitString(string s, string sep)[]{
 int offset=0, len=0, i=0, pos=0
 
 //evaluate the length beforehands...
 while (findPlainText(s[pos:], sep, offset, len, true)){
  pos += offset+len
  i++
 } 
 //....for a late allocation
 string ret[i+1] 

 i=0; pos=0
 while (findPlainText(s, sep, offset, len, true)){
  ret[i++] = s[0:offset-1]
  s = s[offset+len:]
 }
 ret[i++]=s[0:] //add the last one
 return ret
}

Now the trouble...

Could someone explain to me why this code

string aU[]
string aL[]

aU=mySplitString("A/B/C","/")
aL=mySplitString("a/b/c","/")

print aU[0] aU[1] aU[2] "\n"
print aL[0] aL[1] aL[2] "\n"

fails and this other (just a bare change of statements order)

string aU[]
string aL[]

aU=mySplitString("A/B/C","/")
print aU[0] aU[1] aU[2] "\n"

aL=mySplitString("a/b/c","/")
print aL[0] aL[1] aL[2] "\n"

works?

The first code would print

=>abc
=>abc

The last code would print

=>ABC
=>abc

Re: Basic array allocation in function
Adamarla - Thu Dec 17 04:39:06 EST 2015

It a bit technical... so here's the simple version.

Your array is allocated in memory on the 'stack' in a frame reserved for the function. When the function ends, the frame is un-reserved and will be overwritten by any new variables.

You can't return an array from a function and expect it not to get mangled.

Read up on how stacks and heaps work for details.

Re: Basic array allocation in function
pvselex - Thu Dec 17 05:47:36 EST 2015

Ok. I knew it after all. My programming skills got really rusty after a long time of inactivity ;-)

Then my question is,

In DOORS DXL, are you only supposed to pass a basic array as a parameter to a function?

Shouldn't be some way in DXL to dynamic allocate in the caller memory space from within the called function?

Needless to say that I solved my problems with a DXL Array and a sllight modification of the function which now reads

int mySplitString(Array ar, string s, string sep)

Re: Basic array allocation in function
Mathias Mamsch - Thu Dec 17 06:38:47 EST 2015

int mySplitString(Array ar, string s, string sep)

By the way: The answer to your original question was: NEVER return a simple array from a function!

string mySplitString(string s, string sep)[]{
    ...
}

DXL takes the syntax, but the array is deallocated after the function ends, since it is only valid inside the scope of the function (stack). And from returning a deallocated array all kinds of weird things can happen. The catch here is, that when you do not use the stack a lot, the array contents are still intact in memory and the code seems to work, but it breaks down when the stack memory gets reused and overwritten.

Regards, Mathias

Re: Basic array allocation in function
pvselex - Thu Dec 17 06:44:53 EST 2015

string mySplitString(string s, string sep)[]{
    ...
}

Ok, got that

Thanks to both

I guess DXL can only allocate in local memory