Thanks for the confirmation. It seems to me then that this is not a good solution for my base64 encoding needs since I cannot in general pad my source data to the correct length without first copying it. Its probably worth adding a note to the documentation (and maybe an assert in the code) of transform_width that it is only guaranteed to work if the length of the input sequence in bits is an exact multiple of the number of bits requested for the output sequence Andrew -----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Robert Ramey Sent: Wednesday, January 09, 2008 11:45 AM To: boost@lists.boost.org Subject: Re: [boost] [Boost-users] base 64 encoding Look at this I see: we have one byte 8 bits long. transform_width should transform this in to "pieces" each 6 bits long. So there are two choices. return 1 6 bit piece and throw away 2 bits or return 2 6 bit pieces. This would require 12 bits from the input. Hence one would have to feed it 2 bytes. So that's why it requests 2 input bytes to produce 2 6 bit items. So a couple of "solutions" don't feed it it short strings. (fast, only done at setup, but perhaps burdensome) or alter transformwidth so that requests beyond the end of the input(easy to use, but perhaps slower) So I see that as the current situation. Robert Ramey Eames, Andrew wrote:

I posted this on the boost users group but got no final answer - this looks like a bug to me or am I just using it incorrectly?

Andrew

From: Eames, Andrew Sent: Friday, January 04, 2008 1:13 PM To: 'boost-users@lists.boost.org' Subject: Re: [Boost-users] base 64 encoding

I must be missing something fundamental here. The following code fragment doesn't work (VC++ 8.0 SP1) - the checked iterators in STL catch walking off the end of the source - transform_width is attempting to access the second element of the vector

typedef

base64_from_binary<

transform_width<vector<char>::const_iterator, 6, 8>

> base64_t;

vector<char> hippo(1);

string enc(base64_t(hippo.begin()), base64_t(hippo.end())); // -> checked iterator assertion fires

In basic_text_oprimitive.ipp, the iterator is a pointer so it's possible it may be silently doing something bad

Andrew

From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Robert Ramey Sent: Friday, January 04, 2008 11:58 AM To: boost-users@lists.boost.org Subject: [Spam:***** SpamScore] Re: [Boost-users] base 64 encoding

Take a look at basic_text_oprimitive.ipp around line # 64.

Note that I add "padding" here to address this problem. Perhaps that is the missing

magic. Hmmm. perhaps that code should be part of the iterator.

Also look at the code text_iterators_base64 in the serialization test suite.

Robert Ramey

"Eames, Andrew" <andrew@cognex.com> wrote in message news:8F37BF6F420455468C4BD57DD6BE199004C6146B@cobra.pc.cognex.com...

But there is still the problem with running off the end of the source - If the source is not a multiple of 3 bytes then the input iterator will run off the end of the input sequence which can cause an error.

Andrew

From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Robert Ramey Sent: Thursday, January 03, 2008 6:47 PM To: boost-users@lists.boost.org Subject: Re: [Boost-users] base 64 encoding

I had to separately record the number of bytes. Then when I decode, just pull off that number of bytes.

Robert Ramey

"Eames, Andrew" <andrew@cognex.com> wrote in message news:8F37BF6F420455468C4BD57DD6BE199004C613F8@cobra.pc.cognex.com...

Hi,

I'm trying to encode base64 data by composing base64_from_binary with transform_width but this doesn't appear to work correctly when the data is not a multiple of 3 long. What is the correct way to handle this - do I have to handle the padding myself by extending the input data and then patching the tail of the result?

Thanks

Andrew

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