atoi() confusion 1

[Kalisto]

Below is a code fragment, that I am using to try and check that a drive string entered points to a valid drive.

//Check to see if the drive is a valid drive
char* s = new char;
*s = ptrTarget[0];

int nDrv = atoi(s);
if (!_chdrive(nDrv))
{
	AfxMessageBox("The Target Drive does not exist !",MB_OK);
	return; 
}

Watching via the debugger, nDrv is only ever set to 0, which implies that atoi() cannot convert the current value into an integer.

ptrTarget is defined elsewhere in the same function as being a char*, and contains the string "Q:\\test", which is not a valid path on my PC.

So my starter for 10 is, whats happening here that I don't understand ?

And as a bonus question, is _chdrive() the easiest way to check if a drive is valid (I know I still need to handle the fact that the string might be upper or lower case)

K

 

[Cagliostro]

I guess ptrTarget is a char** or a char[][]?
and ptrTarget[0] is something like "3" (3 = disk C)?

Ion Filipski

ICQ: 95034075
AIM: IonFilipski
filipski@excite.com

 

[LazyMe]

This is what happens (ptrTarget="Q:\\test&quot:


char* s = new char;
*s = ptrTarget[0]; //*s now = 'Q'

int nDrv = atoi(s); //nDrv=atoi("Q&quot->you see what's wrong here? You can't convert a Q to an integer... it's not a number.


Greetings,
Rick

 

[Kalisto]

Surely internally the q is stored as 113 ('q' iirc) and not as q.

or am I missing your point entirely ?

K

 

[Cagliostro]

no, it should not be 'Q' nor "Q", only a valid "number"
like "20", not '20'
or "3" and not '3' (disk C)

Ion Filipski

ICQ: 95034075
AIM: IonFilipski
filipski@excite.com

 

[Kalisto]

Damn, I just came rushing back here when I realised what I had done, to post that I am just plain stupid.

I know, I have to convert the drive letter into a number first.

Sorry, and thanks for the hints that I didn't notice.

K

 

[Cagliostro]

in this case forget atoi
int nDrv;
if(ptrTarget[0] >= 'a' and ptrTarget[0] >= 'z')
{
nDrv = (int)ptrTarget[0] - 'a' + 1;
}else if(ptrTarget[0] >= 'A' and ptrTarget[0] >= 'Z')
{
nDrv = (int)ptrTarget[0] - 'A' + 1;
}else is wrong drive letter

if (!_chdrive(nDrv))
{

Ion Filipski

ICQ: 95034075
AIM: IonFilipski
filipski@excite.com

 

[Cagliostro]

sorry:
ptrTarget[0] <= 'z'

Ion Filipski

ICQ: 95034075
AIM: IonFilipski
filipski@excite.com

 

[Kalisto]

Cheers, that more or less how I had re-written it, but it's nice to know that I can still do soemthings right, after my recent debacles !)

K