# [C++] Seeking a good "buffer" class.

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So basically, when I send/receive packets, I'd like to put the raw data (a sequence of 'char's) into a container within my data struct -- let's call it Packet -- for subsequent use. Some things I could theoretically place inside the Packet struct to store the raw data: 1. char buffer[X] - a char array... simple, but I would really like something that is more dynamic. i.e. I'd like to be able to use whatever size data I want and just specify a 'length' in the packet. Because C++ is cool, copying a Packet by-value will still work, because arrays within a struct are copied element-by-element (not just the pointer). 2. std::string - a string... really pretty - I can both easily store the raw data I read in into a string and easily get it back out using c_str(). Once again, copying a Packet by-value is still a breeze, because std::strings copy appropriately. The problem? If there are any 0's in my raw data - and there definitely can be - the string will terminate at that point. Basically, I was thinking of something like a string, but that specifies a length instead of being null-terminated. I have to imagine this would be a highly used class, and I would be shocked if something didn't exist for this purpose. Has anyone done socket programming and had a similar desire for a dynamically-sized buffer that copies by-value appropriately? I guess what I'm wondering is, does anyone know of a class like this, or have suggestions as to what would work well? To program this from scratch would be annoying.

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std::vector<char>?

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Yes, I should have put that (or std::list<char>) as one of the possibilities...
the problem with that is

A. it seems needlessly bulky and

B. I can neither easily do something like:
vec = some_c_string;
nor:
memcpy(buffer, &vec.c_str(), vec.length());
(both of which I can do with strings - and are incredibly useful when sending/receiving data)
I'd have to iterate which, again just seems very ... ugly

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Quote:
 Yes, I should have put that (or std::list) as one of the possibilities...the problem with that is

std::vector is suitable for a buffer. std::list is not.

Quote:
 A. it seems needlessly bulky

Really? std::vector has minimal overhead. The size of a vector is usually 3 pointers + the size of the contained buffer.

Quote:
 B. I can neither easily do something like:vec = some_c_string;nor:memcpy(buffer, &vec.c_str(), vec.length());(both of which I can do with strings - and are incredibly useful when sending/receiving data)I'd have to iterate which, again just seems very ... ugly

You can do:
memcpy(buffer, &vec[0], vec.length()); //requires vec.length() >= 1

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Quote:
 Original post by Browser12vec = some_c_string;

vec.resize(strlen(some_c_string));
std::copy(some_c_string, some_c_string + vec.size(), vec.begin());

Quote:
 Original post by Browser12memcpy(buffer, &vec.c_str(), vec.length());

std::copy(vec.begin(), vec.end(), buffer);

[EDIT]
See Antheus' post below for a better "vec = some_c_string" approach ;)

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Quote:
 Original post by Browser12(or std::list) as one of the possibilities...

The worst imaginable option. list is a linked list, which would contain back and next pointers for each char.

Quote:
 A. it seems needlessly bulky and

std::string is bulkier than std::vector.

Quote:
 B. I can neither easily do something like: vec = some_c_string;

vec.assign(some_c_string, some_c_string + strlen(some_c_string));

Quote:
 memcpy(buffer, &vec.c_str(), vec.length());

	std::string s("Hello World");	std::vector<char> v;	v.assign(s.begin(), s.end()); // string to vector	s.assign(v.begin(), v.end()); // vector to string

Quote:
 (both of which I can do with strings - and are incredibly useful when sending/receiving data)

Except for the 0 value in data received from network, which can quickly happen.

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Hmm, guess I'll be trying out std::vector, then. Chalk this one up to inexperience with vectors! (I thought they worked similarly to linked lists - oops.)

Thanks a bunch guys~

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std::string can handle embedded 0's just fine. C-style strings can't but std::string isn't a C-style string.

std::vector is still the better way to go though. If your data is not actually a string and you go sticking it in a std::string it will just confuse everybody.

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Quote:
Original post by Antheus
Quote:
 A. it seems needlessly bulky and

std::string is bulkier than std::vector.
QFT! I was going to point that out if nobody else did.

I somehow knew the answer was std::vector before I even opened this thread.

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How is string bulkier than vector?

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Why would you want to keep copying buffers by value all over the place? If anything you should have a buffer that does NOT copy by value, just a simple wrapper around a pointer. boost::asio has boost::asio::const_buffer and boost::asio::mutable_buffer for this purpose. You access it using a specific type using boost::asio::buffer_cast.

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Quote:
 Original post by theOcelotHow is string bulkier than vector?

It typically includes a small char[] in its data layout to optimize for the common case where strings are short.

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Quote:
Original post by Zahlman
Quote:
 Original post by theOcelotHow is string bulkier than vector?

It typically includes a small char[] in its data layout to optimize for the common case where strings are short.

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Quote:
 Original post by cache_hitWhy would you want to keep copying buffers by value all over the place? If anything you should have a buffer that does NOT copy by value, just a simple wrapper around a pointer. boost::asio has boost::asio::const_buffer and boost::asio::mutable_buffer for this purpose. You access it using a specific type using boost::asio::buffer_cast.
Who said anything about passing vectors by value?

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Quote:
Original post by iMalc
Quote:
 Original post by cache_hitWhy would you want to keep copying buffers by value all over the place? If anything you should have a buffer that does NOT copy by value, just a simple wrapper around a pointer. boost::asio has boost::asio::const_buffer and boost::asio::mutable_buffer for this purpose. You access it using a specific type using boost::asio::buffer_cast.
Who said anything about passing vectors by value?

I thought the OP did, unless I missed something.

Quote:
 Has anyone done socket programming and had a similar desire for a dynamically-sized buffer that copies by-value appropriately?

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Quote:
Original post by cache_hit
Quote:
Original post by iMalc
Quote:
 Original post by cache_hitWhy would you want to keep copying buffers by value all over the place? If anything you should have a buffer that does NOT copy by value, just a simple wrapper around a pointer. boost::asio has boost::asio::const_buffer and boost::asio::mutable_buffer for this purpose. You access it using a specific type using boost::asio::buffer_cast.
Who said anything about passing vectors by value?

I thought the OP did, unless I missed something.

Quote:
 Has anyone done socket programming and had a similar desire for a dynamically-sized buffer that copies by-value appropriately?
Oh... that! (slaps forehead). I took that to mean that it copied the things being inserted into the container rather than just storing pointers in the container.
Perhaps the OP will clarify that one.

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Shalom

I have some Buffer classes here.

The SendBuffer/ReceiveBuffer are I think mostly useful when writing to a disk. SendCompressedBuffer/ReceiveCompressedBuffer are what I use when a network is involved.

Brian Wood
http://webEbenezer.net
(651) 251-9384

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