Re: Can this conversion code be simplified?


Joe Wright wrote:
Eric Lilja wrote:
Hello, I have IPv4-numbers in the following format:
"\\x0A\\x11\\x8C\\x01"

Now I need each byte as an int. I wrote the following test program:
#include <stdio.h>
#include <stdlib.h>

static void to_ip(const char *, int *);
static void extract_substring(const char *, u_short, u_short, char *);

int
main(void)
{
const char *ip_as_string="\\x0A\\x11\\x8C\\x01";

int ip[4];

to_ip(ip_as_string, ip);

printf("IP is %i.%i.%i.%i\n", ip[0], ip[1], ip[2], ip[3]);

return 0;
}

static void
extract_substring(const char *s, u_short start, u_short end, char *out)
{
u_short out_index = 0;

for(; start <= end; ++start)
out[out_index++] = s[start];

out[++start] = '\0';
}

static void
to_ip(const char *ip_as_string, int *ip)
{
char sub[5] = "0";
char *ptr = sub;
u_short start_index = 1;
u_short end_index = 3;
u_short i = 0;

for(; i < 4; ++i)
{
extract_substring(ip_as_string, start_index, end_index, ptr + 1);

start_index += 4;
end_index += 4;

ip[i] = strtol(sub, NULL, 16);
}
}

It compiles cleanly and produces the following output:
$ ./convert_to_ip.exe
IP is 10.17.140.1


But since I am very poor on string manipulations in C, I'm guessing
there are alot cleaner ways to do this. Please help me improve the
code. It's a homework problem, but as you can see I attempted to solve
it myself first.

/ E

I don't know yet. When I compile the code you posted I get..

s2ip.c:5: parse error before "u_short"
s2ip.c:19: parse error before "u_short"
s2ip.c: In function `extract_substring':
s2ip.c:21: `u_short' undeclared (first use in this function)
s2ip.c:21: (Each undeclared identifier is reported only once
s2ip.c:21: for each function it appears in.)
s2ip.c:21: parse error before "out_index"
s2ip.c:22: `start' undeclared (first use in this function)
s2ip.c:22: `end' undeclared (first use in this function)
s2ip.c:23: `out' undeclared (first use in this function)
s2ip.c:23: `out_index' undeclared (first use in this function)
s2ip.c:23: `s' undeclared (first use in this function)
s2ip.c: In function `to_ip':
s2ip.c:32: `u_short' undeclared (first use in this function)
s2ip.c:32: parse error before "start_index"
s2ip.c:35: `i' undeclared (first use in this function)
s2ip.c:36: `start_index' undeclared (first use in this function)
s2ip.c:36: `end_index' undeclared (first use in this function)

Which puts me off a bit.

Hmm, I'm compiling using gcc with the flags -ansi -pedantic and I
thought that would turn off any compiler extension. Anyway, u_short is
simply a typedef for unsigned short int.


--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

/ E

.

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