problem with return

[cdg]

Could anyone tell me why a function return with this program is not
returning to "main". The program will compile and should be
self-explanatory. And any suggestions for improvements would be appreciated
also.
The function is HashMilliTime at the end of the program.

#include <sys/timeb.h>
#include <iostream.h>
#include <string.h>
#include <stdlib.h>

unsigned short GetMilliTime(un signed short *); //function prototype
unsigned HashMilliTime (char[], int); //function prototype

void main()
{
unsigned short mltm(0); //milli-seconds for time
char mltmch[5] = {0}; //milli-seconds as character array
int mltmln(0); //length of milli-seconds as character array
// unsigned h(0); //hashed milli-seconds

GetMilliTime(&m ltm);

cout<<mltm<<end l; //test only remove later

itoa( mltm, mltmch, 10 );

cout<<mltmch<<" char"<<endl; //test only remove later

mltmln = strlen(mltmch);

cout<<mltmln<<e ndl; //test only remove later

cout<<mltmch<<" before"<<endl; //test only remove later

HashMilliTime(m ltmch, mltmln);

//**The returned unsigned int will not print here**
cout<<mltmch<<" should be same as h"<<endl; //test only remove later

cout<<mltmln<<e ndl; //test only remove later

}

unsigned short GetMilliTime(un signed short *mltm)
{
struct _timeb tstruct;
_ftime( &tstruct );
*mltm = tstruct.millitm ;
return *mltm;
}

unsigned HashMilliTime (char key[], int len )
{
char *p = key;
unsigned h = 0;
int i(0);
unsigned x(0);

for ( i = 0; i < len; i++ )
{
h += p[i];
h += ( h << 10 );
h ^= ( h >> 6 );
}

h += ( h << 3 );
h ^= ( h >> 11 );
h += ( h << 15 );

cout<<len<<" hash"<<endl; //test only remove later
cout<<h<<" hash"<<endl; //test only remove later

return h;
x = len + 5; //test only remove later
return x; //test only remove later
}

[Victor Bazarov]

Re: problem with return

cdg wrote:[color=blue]
> Could anyone tell me why a function return with this program is not
> returning to "main".[/color]

The program has undefined behaviour. You're most likely stepping all over
the stack by overrunning the bounds of a local array.
[color=blue]
> The program will compile[/color]

No, it won't. At least on my system.
[color=blue]
> and should be
> self-explanatory. And any suggestions for improvements would be appreciated
> also.[/color]

First and foremost, your program contains non-standard constructs, like
'<sys/timeb.h>', '<iostream.h>' , "void main", 'itoa', '_timeb', '_ftime'.
The behaviour of the program with all those is _undefined_ in Standard
C++ terms. Making certain concessions, I can probably tell you what
_else_ is wrong with it. See below.
[color=blue]
> The function is HashMilliTime at the end of the program.
>
> #include <sys/timeb.h>
> #include <iostream.h>
> #include <string.h>
> #include <stdlib.h>
>
> unsigned short GetMilliTime(un signed short *); //function prototype
> unsigned HashMilliTime (char[], int); //function prototype
>
> void main()
> {
> unsigned short mltm(0); //milli-seconds for time
> char mltmch[5] = {0}; //milli-seconds as character array[/color]

So, 'mstmch' contains only 5 elements.
[color=blue]
> int mltmln(0); //length of milli-seconds as character array
> // unsigned h(0); //hashed milli-seconds
>
> GetMilliTime(&m ltm);
>
> cout<<mltm<<end l; //test only remove later
>
> itoa( mltm, mltmch, 10 );[/color]

Are you sure that converting 'mltm' here does not step _over_ the
boundary of 'mltmch' array? Remember, it only has 5 elements, thus
leaving only 4 characters in the C-string.
[color=blue]
>
> cout<<mltmch<<" char"<<endl; //test only remove later
>
> mltmln = strlen(mltmch);
>
> cout<<mltmln<<e ndl; //test only remove later
>
> cout<<mltmch<<" before"<<endl; //test only remove later
>
> HashMilliTime(m ltmch, mltmln);
>
> //**The returned unsigned int will not print here**
> cout<<mltmch<<" should be same as h"<<endl; //test only remove later
>
> cout<<mltmln<<e ndl; //test only remove later
>
> }
>
> unsigned short GetMilliTime(un signed short *mltm)
> {
> struct _timeb tstruct;
> _ftime( &tstruct );
> *mltm = tstruct.millitm ;
> return *mltm;
> }
>
> unsigned HashMilliTime (char key[], int len )
> {[/color]

Add

assert(len < 5);

here.
[color=blue]
> char *p = key;
> unsigned h = 0;
> int i(0);
> unsigned x(0);
>
> for ( i = 0; i < len; i++ )
> {
> h += p[i];
> h += ( h << 10 );
> h ^= ( h >> 6 );
> }
>
> h += ( h << 3 );
> h ^= ( h >> 11 );
> h += ( h << 15 );
>
> cout<<len<<" hash"<<endl; //test only remove later
> cout<<h<<" hash"<<endl; //test only remove later
>
> return h;
> x = len + 5; //test only remove later
> return x; //test only remove later[/color]

You cannot "test only" any code _after_ a 'return' statement in
your function.
[color=blue]
> }
>
>[/color]

V
--
Please remove capital As from my address when replying by mail

[cdg]

Re: problem with return

Thanks for your post.

And I am not very far in along in what I have learned about C++, and it is
all self-taught. But your post did help me to understand about "defined
behaviour". And what is needed to write up-to-date programs.
Also, I figured out why the return value wasn`t being returned. I was
writing it incompletely, since the function call needed a Lvalue. This was
the problem, not the array size. Since milli-seconds would never go over
1000, or possibly 999, if milli-seconds starts at zero.
And the second return was an obvious mistake, too.