Lafer <> wrote:
> I am attempting to write a terminal interface program using PowerPC
> Assembly/C, where I am using an integer-to-ASCII conversion algorithm.
> Unfortunately, I have run into some difficulties that seem to deal
> with the syntax/character types that am I using. Below is a segment of
> my code which is intended to convert an integer to an array of ASCII
> digits:
>> > char * inttoascii(int val)
>> > {
>> > int i, temp1, temp2;
>> > i = 0;
>> > char * str;
>> > temp1 = 1;
>> > if(val < 0)
>> > {
>> > str[i] = '-';
You have some bad bug here: str has never been initialized, so it
probably points to some random place in memory. You have to allocate
enough memory and assign that to str before you can start to use it.
(There was another thread today about the question how long the
string can become in the worst case, i.e. how much memory you need
to allocate to be on the safe side.)
>> > val = val*-1;
>> > i++;
>> > }
>> > while(val > temp1)
>> > {
>> > temp1 = temp1*10;
>> > }
Lets assume that val is e.g. is 17. Then temp1 is now 100.
>> > while(temp1 >= 10)
>> > {
>> > temp1 = temp1/10;
First time round temp1 is 10, thesecond time it's 1.
>> > temp2 = val/temp1;
The first time round temp2 will be 1, the second time it's going
to be 17, which you probably don't want. You need another line
where you do
val %= temp1;
so that you get temp2 set to 7 on the second time through the loop.
>> > str[i] = temp2+48; *****
Making sure that this works also with non-ASCII representations is
extremely simple and doesn't cost you anything but just makes your
program easier to read. Use
str[ i ] = temp2 + '0'.
(of course only after having assigned enough memory to str).
>> > i++;
>> > }
>> > str[i] = '\0';
>> > return(str);
Now here's another possible pitfall. If you should make str an
automatic array (instead of allocating memory for the pointer or
making it a static array) you would return a value that goes
out of scope the moment you leave the function and thus can't be
used by the caller.
>> > }
> The ***** line is where I'm having my problems; presumably adding 48
> to a string element (i.e., a character) should convert that value to
> its ASCII equivalent so it can be displayed on my terminal screen, but
> when debugging the problem line doesn't seem to be doing anything at
> all; presumably this is an issue of syntax that you can help me with.
> I have also tried '0' and '0x30' in place of 48.
> Another problem I have is with copying strings into other strings, for
> example I have a help message that says:
> strcopy(output, "+ for add, - for subtract, ? for help");
> where strcopy is the following function:
>> > void strcopy(char b[], char a[])
>> > {
>> > int i;
>> >
>> > for (i = 0; a[i] != '\0'; i++)
>> > b[i] = a[i];
>> > b[i] = '\0';
>> > }
> When I try to do this conversion it gives me a machine check exception
> in the simulator I'm using (SingleStep) something about error, memory
> access in 0x0000000D) which it doesn't do if I use a normal strcopy
> syntax where a and b are both declared as character pointers e.g. char
> *a, char *b. Note that I do not have the standard library, standard
> i/o or any other such libraries at my disposal for this program.
Looks a lot as if you pass an unitialized pointer to that function.
If you do something like
char *output;
strcopy(output, "+ for add, - for subtract, ? for help");
you're in for such an error because 'output' doesn't point to any
memory you own. It might just by chance point to memory location
0x0D (but don't count on that). BTW, why don't you use the classic
construct
void strcopy( char *b, const char *a )
{
while ( *b++ = *a++ )
/* empty */ ;
}
Regards, Jens
--
\ Jens Thoms Toerring ___
\__________________________
http://www.toerring.de
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