# [erlang-questions] Help! a log dump function from C.

Hynek Vychodil <>
Wed Apr 22 09:27:29 CEST 2009

```There are many many approaches to do this,  one that doesn't use io or
io_lib follows:

-module(dump_hex).

-compile(inline).

-export([dump_hex/1]).

dump_hex(L) -> lists:reverse(dump_hex(0, L, [])).

dump_hex(_, [pad | _], R) -> R;
dump_hex(_, [], R) -> R;
dump_hex(N,
[B1, B2, B3, B4, B5, B6, B7, B8, B9, B10, B11, B12, B13,
B14, B15, B16
| T],
R) ->
dump_hex(N + 16, T,
[[\$\s | hex(X)]
|| X
<- [B1, B2, B3, B4, B5, B6, B7, B8, B9, B10, B11, B12,
B13, B14, B15, B16]],
" - ",
[print(X)
|| X
<- [B1, B2, B3, B4, B5, B6, B7, B8, B9, B10, B11, B12,
B13, B14, B15, B16]],
\$\n]
| R]);
dump_hex(N, L, R) ->
dump_hex(N,
L ++
R).

[nibble(X bsr 28), nibble(X bsr 24), nibble(X bsr 20),
nibble(X bsr 16), nibble(X bsr 12), nibble(X bsr 8),
nibble(X bsr 4), nibble(X)].

hex(X) -> [nibble(X bsr 4), nibble(X)].

nibble(X) -> nibble_(X band 15).

nibble_(X) when X < 10 -> X + \$0;
nibble_(X) -> X + \$a.

print(X) when X < \$\s, X > 126 -> \$.;
print(X) -> X.

Usage:

1> c(dump_hex).
{ok,dump_hex}
2> io:put_chars(dump_hex:dump_hex("teststr1234567890abcd")).
00000000: 74 65 73 74 73 74 72 31 32 33 34 35 36 37 38 39 - teststr123456789
00000010: 30 61 62 63 64                                  - 0abcd
ok

On Wed, Apr 22, 2009 at 2:03 AM, feiman <> wrote:

> hi,All
>   I have a function from C,which print out detail hex information
> about a buffer,who can help me "translate" it into Erlang?
>
> when I run
>        const char *teststr = "teststr1234567890abcd";
>
>        dump_hex((const unsigned char *)teststr,strlen(teststr));
>
> it print out
>
> 00000000: 74 65 73 74 73 74 72 31 32 33 34 35 36 37 38 39 -
> teststr123456789
> 00000010: 30 61 62 63 64                                  - 0abcd
>
>
> void dump_hex( const unsigned char *buf, int len)
> {
>        int i;
>        int nlocal;
>        const unsigned char *pc;
>        char *out;
>        const unsigned char *start;
>        char c;
>        char line[100];
>
>        start = buf;
>
>        while (len > 0)
>        {
>                sprintf(line, "%08x: ", buf - start);
>                out = line + 10;
>
>                for (i = 0, pc = buf, nlocal = len; i < 16; i++, pc++)
>                {
>                        if (nlocal > 0)
>                        {
>                                c = *pc;
>
>                                *out++ = NIBBLE((c >> 4) & 0xF);
>                                *out++ = NIBBLE(c & 0xF);
>
>                                nlocal--;
>                        }
>                        else
>                        {
>                                *out++ = ' ';
>                                *out++ = ' ';
>                        }                       /* end else */
>
>                        *out++ = ' ';
>                }                       /* end for */
>
>                *out++ = '-';
>                *out++ = ' ';
>
>                for (i = 0, pc = buf, nlocal = len;
>                        (i < 16) && (nlocal > 0);
>                        i++, pc++, nlocal--)
>                {
>                        c = *pc;
>
>                        if ((c < ' ') || (c >= 126))
>                        {
>                                c = '.';
>                        }
>
>                        *out++ = c;
>                }                       /* end for */
>
>                *out++ = 0;
>
>                llog(L_NOTICE,"%s", line);
>
>                buf += 16;
>                len -= 16;
>        }                               /* end while */
> }                               /* end dump */
>
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>
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>

--
--Hynek (Pichi) Vychodil