Quoth hahahahacker2009 <[email protected]>:
> I'm writing a program that use uvlong on 9legacy raspberry pi.
> uvlong n;
> scanf("%lld", &n);
> print("%lld", n);
> But after compiling the program and input a small number (8), it print 0. I
> modified it and compile with pcc, but it print a very big number then.
> unsigned long works. What's the problem with uvlong?
the problem is with scanf; it doesn't handle that case:
static int icvt_n(FILE *f, va_list *args, int store, int width, int
type){
if(store){
--ncvt; /* this assignment doesn't count! */
switch(type){
case 'h': *va_arg(*args, short *)=nread; break;
case 'n': *va_arg(*args, int *)=nread; break;
case 'l':
case 'L': *va_arg(*args, long *)=nread; break;
}
}
return 1;
}
A patch to fix this would be welcome, but Plan 9 code doesn't
tend to use scanf; Unix code is also best off avoiding scanf,
it's an API that feels convienient but has a number of pitfalls.
Specifically, if there's a format mismatch, the remainder of the
input remains buffered, and you need fiddly error handling code
to consume it.
Here's probably how I'd write it:
char *e;
uvlong n;
ln = Brdstr(bfd, '\n', 1);
n = strtoull(ln, &e, 0);
if(*e != '\0')
print("trailing junk\n");
printf("%llud\n", n);
free(ln);
it's a little more code, but it keeps working as the code gets
more functional.
If I want to handle more complex input, I'd tend to reach for
tokenize(2) -- which loosely the format a lot of programs use.
For example:
char *e, *sp[4];
uvlong n1, n2;
int n;
ln = Brdstr(bfd, '\n', 1);
n = tokenize(ln, sp, nelem(sp));
switch(n){
case 1:
if(strcmp(sp[0], "greet") != 0)
sysfatal("unknown command");
print("hello world\n");
break;
case 3:
if(strcmp(sp[0], "sum") != 0)
sysfatal("unknown command");
n1 = strtoull(sp[1], &e, 0);
if(*e != 0)
sysfatal("invalid number\n");
n2 = strtoull(sp[2], &e, 0);
if(*e != 0)
sysfatal("invalid number\n");
print("2*arg: %lld\n", n1+n2);
break;
default:
sysfatal("invalid line");
break;
}
free(ln);
(Subtle point: I have n+1 entries in sp[] to detect that
too many fields were passed).
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