Re: Command Languages Versus Programming Languages

mas@a4.home writes:

On 2024-11-20, Rainer Weikusat <rweikusat@talktalk.net> wrote:

Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:
>
Assuming that p is a pointer to the current position in a string, e is a
pointer to the end of it (ie, point just past the last byte) and -
that's important - both are pointers to unsigned quantities, the 'bulky'
C equivalent of [0-9]+ is
>
while (p < e && *p - '0' < 10) ++p;
>
That's not too bad. And it's really a hell lot faster than a
general-purpose automaton programmed to recognize the same pattern
(which might not matter most of the time, but sometimes, it does).

>
int
main(int argc, char **argv) {
unsigned char *p, *e;
unsigned char mystr[] = "12#45XY ";
>
    p = mystr;
    e = mystr + sizeof(mystr);
    while (p < e && *p - '0' < 10) ++p;

The code I'm actually using is

 while (p < e && (unsigned)*p - '0' < 10)
        ++p;

I just omitted that when posting this beause I mistakenly assumed that
it probably wasn't needed, ;-). You could have pointed this out instead
of trying to dress it up as some sort of mystery problem¹. Especially as
I did mention that using unsigned arithmetic was necessary (should
really be self-evident).

I should really have replied with

[rw@doppelsaurus]/tmp#gcc a.c
a.c: In function 'main':
a.c:12:5: error: unknown type name 'size_t'
   12 |     size_t xlen = p-mystr;
      |     ^~~~~~
a.c:1:1: note: 'size_t' is defined in header '<stddef.h>'; did you forget to '#include <stddef.h>'?
  +++ |+#include <stddef.h>
    1 | int
a.c:13:5: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   13 |     printf("digits: '%.*s'\n", (int) xlen, mystr);
      |     ^~~~~~
a.c:13:5: warning: incompatible implicit declaration of built-in function 'printf'
a.c:1:1: note: include '<stdio.h>' or provide a declaration of 'printf'
  +++ |+#include <stdio.h>
    1 | int

as code which cannot even be compiled as no runtime behaviour.