Convert 1-byte number to decimal

Question

First of all I'm sorry for the confusing title. I'm reading Adobe's specs of SWF and I saw a statement I'm not really sure how to code.

A one-byte version number follows the signature. The version number is not an ASCII character, but an 8-bit number. For example, for SWF 4, the version byte is 0x04, not the ASCII character “4” (0x34).

This effectively means that 0x20 is not a space, but actually the number 20.

Now, let's say I have this:

unsigned char c[1] = { 0x20 };

How would I get an integer with the value 20 out of c?

EDIT:

It turns out that not what I'm looking for. The byte with the version actually follows this scheme: Chart of SWF versions to Flash versions

I read that as saying it would be the number `0x20`, not `20`... — Oliver Charlesworth, Jan 26 '15 at 00:17
@OliverCharlesworth No, read again. `0x04` is not `EOT`, but actually the number `4` (which's HEX representation is `0x34`). — alexandernst, Jan 26 '15 at 00:18
Sure, but 0x4 and 4 are the same thing. 0x20 and 20 are not. — Oliver Charlesworth, Jan 26 '15 at 00:19
@OliverCharlesworth I'm not really sure about that. Mind to make a simple printf with it? — alexandernst, Jan 26 '15 at 00:20
0x20 and 20 are not the same thing. 0x04 IS 4. 0x20 (which is hex) is actually the number 32 (if you use %d - it IS 20 with %x) — Toam, Jan 26 '15 at 00:20
@alexandernst: yes, Toam is saying the same thing as me. You are misinterpreting the spec. — Oliver Charlesworth, Jan 26 '15 at 00:21
Also note that since the question wants an integer output, %d is the correct format to use. 0x20 should return 32, not 20. with %x, FF would return "FF" which is not an integer. — Toam, Jan 26 '15 at 00:22
@OliverCharlesworth Again, as what Toam said. Version 11 of SWF is `0x11`, and not `0x0b`. i need to get an integeer out of that (weird imho) representation. — alexandernst, Jan 26 '15 at 00:24
http://stackoverflow.com/questions/28139264/how-to-convert-decimal-back-bcd/ — BLUEPIXY, Jan 26 '15 at 00:24
I think SWF 11 IS 0x0b: http://stackoverflow.com/questions/4351370/how-can-i-determine-what-flash-player-version-a-swf-was-published-for — Toam, Jan 26 '15 at 00:26
@Toam No, it's not. I have a valid SWF v11 file and it's 0x11. — alexandernst, Jan 26 '15 at 00:27
Nowhere does the spec say "convert the byte value to a hex string representation, then interpret the digits as decimal, and then convert back". If that's *genuinely* what one needs to do, then that's a terrible spec. — Oliver Charlesworth, Jan 26 '15 at 00:27
You are sure it is not SWF 17 and Flash 11: http://stackoverflow.com/questions/9537076/chart-of-swf-versions-to-flash-versions — Toam, Jan 26 '15 at 00:29
@alexandernst: "If you need to knows the mapping between Flash Player / AIR names to SWF version (for example, 11.4 is SWF 17)," (page 13) — rici, Jan 26 '15 at 00:39
@OliverCharlesworth You are right, indeed. I should actually use the table you linked to convert to the correct version. — alexandernst, Jan 26 '15 at 00:40

Iharob Al Asimi · Answer 1 · 2015-01-26T00:24:34.467

1

Try this

char string[16];
int  value;
unsigned char c[1] = { 0x20 };

snprintf(string, sizeof(string), "%x", c[0]);
value = strtol(string, NULL, 10);

this will work as long as the hex representation of the number has a textual decimal equivalent, i.e. it wont work for 0xA0 for example.

edited Jan 26 '15 at 00:24

answered Jan 26 '15 at 00:19

Iharob Al Asimi

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That will reinterpret a byte of what we used to call BCD as a decimal number (although it's clunky: you could just do `c[0] - 6*(c[0]>>4)`), but it seems highly unlikely that it what is really required here. – rici Jan 26 '15 at 00:41

Convert 1-byte number to decimal

1 Answers1