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change function

 
 
Larry
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Posts: n/a
 
      01-29-2010
Hi,

I would like to turn this function:

std::string Socket::ReceiveBytes() {
std::string ret;
char buf[1024];

while (1) {
u_long arg = 0;
if (ioctlsocket(s_, FIONREAD, &arg) != 0)
break;

if (arg == 0)
break;

if (arg > 1024) arg = 1024;

int rv = recv (s_, buf, arg, 0);
if (rv <= 0) break;

std::string t;

t.assign (buf, rv);
ret += t;
}

return ret;
}

into something like:

bool Socket::ReceiveBytes(char * buffer, const int buffersize);

how should I change it internally?

thanks
 
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Larry
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Posts: n/a
 
      01-29-2010
"Larry" <(E-Mail Removed)> ha scritto nel messaggio
news:4b635ddc$0$1137$(E-Mail Removed). ..

> into something like:


this is what I have figure out so far: (untested)


#include <algorithm>

int Socket::ReceiveBytes(char * buffer, int buffersize)
{
if(buffersize > 3276
buffersize = 32768;

char temp[32768];
int byrv = 0;

while (1)
{
u_long arg = 0;

if (ioctlsocket(s_, FIONREAD, &arg) != 0)
return -1;

if (arg == 0)
return byrv;

if (arg > buffersize)
arg = buffersize;

int rv = recv (s_, temp, arg, 0);

if (rv <= 0)
return -1;

std::copy(temp, temp + rv, buffer);
byrv += rv;
}
}

 
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Larry
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Posts: n/a
 
      01-30-2010
"Larry" <(E-Mail Removed)> ha scritto nel messaggio
news:4b637617$0$820$(E-Mail Removed).. .

> this is what I have figure out so far: (untested)


#include <algorithm>

int Socket::ReceiveBytes(char * buffer, int buffersize)
{
if(buffersize > 3276
buffersize = 32768;

char temp[32768];

u_long arg = 0;

if (ioctlsocket(s_, FIONREAD, &arg) != 0)
return -1;

if (arg == 0)
return 0;

if (arg > buffersize)
arg = buffersize;

int rv = recv (s_, temp, arg, 0);

if (rv <= 0)
return -1;

if (rv == 0)
return 0;

if (rv > 0)
std::copy(temp, temp + rv, buffer);

}

where FIONREAD:

Determine the amount of data which can be read atomically from socket s.
argp points to an unsigned long in which ioctlsocket stores the result. If s
is stream oriented (for example, type SOCK_STREAM), FIONREAD returns an
amount of data which can be read in a single recv; this may or may not be
the same as the total amount of data queued on the socket. If s is message
oriented (for example, type SOCK_DGRAM), FIONREAD returns the size of the
first datagram (message) queued on the socket.

So I basically I will recv according to ioctlsocket. if the latter is > then
buffersize I will read buffersize (arg = buffersize) if it's
less...well...be just happy with that...if it's 0 or less don't even bother
copying the buffer and return accordingly.

that's all

what about my idea?

thanks

 
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Larry
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Posts: n/a
 
      01-30-2010
"Larry" <(E-Mail Removed)> ha scritto nel messaggio
news:4b637617$0$820$(E-Mail Removed).. .

> this is what I have figure out so far: (untested)


#include <algorithm>

int Socket::ReceiveBytes(char * buffer, int buffersize)
{
if(buffersize > 3276
buffersize = 32768;

char temp[32768];

u_long arg = 0;

if (ioctlsocket(s_, FIONREAD, &arg) != 0)
return -1;

if (arg == 0)
return 0;

if (arg > buffersize)
arg = buffersize;

int rv = recv (s_, temp, arg, 0);

if (rv <= 0)
return -1;

if (rv == 0)
return 0;

if (rv > 0)
std::copy(temp, temp + rv, buffer);

}

where FIONREAD:

Determine the amount of data which can be read atomically from socket s.
argp points to an unsigned long in which ioctlsocket stores the result. If s
is stream oriented (for example, type SOCK_STREAM), FIONREAD returns an
amount of data which can be read in a single recv; this may or may not be
the same as the total amount of data queued on the socket. If s is message
oriented (for example, type SOCK_DGRAM), FIONREAD returns the size of the
first datagram (message) queued on the socket.

So I basically I will recv according to ioctlsocket. if the latter is > then
buffersize I will read buffersize (arg = buffersize) if it's
less...well...be just happy with that...if it's 0 or less don't even bother
copying the buffer and return accordingly.

that's all

what about my idea?

thanks

 
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Jorgen Grahn
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Posts: n/a
 
      02-03-2010
On Sat, 2010-01-30, Larry wrote:
> "Larry" <(E-Mail Removed)> ha scritto nel messaggio
> news:4b637617$0$820$(E-Mail Removed).. .
>
>> this is what I have figure out so far: (untested)

>
> #include <algorithm>
>
> int Socket::ReceiveBytes(char * buffer, int buffersize)
> {
> if(buffersize > 3276
> buffersize = 32768;
>
> char temp[32768];
>
> u_long arg = 0;
>
> if (ioctlsocket(s_, FIONREAD, &arg) != 0)
> return -1;
>
> if (arg == 0)
> return 0;
>
> if (arg > buffersize)
> arg = buffersize;
>
> int rv = recv (s_, temp, arg, 0);
>
> if (rv <= 0)
> return -1;
>
> if (rv == 0)
> return 0;
>
> if (rv > 0)
> std::copy(temp, temp + rv, buffer);
>
> }


Try compiling it with full warnings enabled before posting -- I spot
at least one compile error. Also please indent with more that 1 space
-- 4 is rather universal.

> where FIONREAD:
>
> Determine the amount of data which can be read atomically from socket s.
> argp points to an unsigned long in which ioctlsocket stores the result. If s
> is stream oriented (for example, type SOCK_STREAM), FIONREAD returns an
> amount of data which can be read in a single recv; this may or may not be
> the same as the total amount of data queued on the socket. If s is message
> oriented (for example, type SOCK_DGRAM), FIONREAD returns the size of the
> first datagram (message) queued on the socket.


It's not clear if you expect your socket to be stream or datagram. Or
what you intend the function to do. It's unusual, I think, to user the
same high-level function for both.

Adding just a tiny bit of documentation would have helped when
discussing it, a lot.

I don't think it's very common for people to use FIONREAD, by the way.
I think there are better options ... but I don't remember exactly and
it's offtopic here anyway.

> So I basically I will recv according to ioctlsocket. if the latter is > then
> buffersize I will read buffersize (arg = buffersize) if it's
> less...well...be just happy with that...if it's 0 or less don't even bother
> copying the buffer and return accordingly.
>
> that's all
>
> what about my idea?


One thing I don't understand is the extra copying. You went from a
std::string to a char* of known length, but why not read straight into
it?

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .
 
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tonydee
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Posts: n/a
 
      02-04-2010
On Jan 30, 7:14*am, "Larry" <(E-Mail Removed)> wrote:
> Hi,
>
> * I would like to turn this function:
>
> std::string Socket::ReceiveBytes() {
> * std::string ret;
> * char buf[1024];
>
> * while (1) {
> * * u_long arg = 0;
> * * if (ioctlsocket(s_, FIONREAD, &arg) != 0)
> * * * break;
>
> * * if (arg == 0)
> * * * break;
>
> * * if (arg > 1024) arg = 1024;
>
> * * int rv = recv (s_, buf, arg, 0);
> * * if (rv <= 0) break;
>
> * * std::string t;
>
> * * t.assign (buf, rv);
> * * ret += t;
> * }
>
> * return ret;
>
> }
>
> into something like:
>
> bool Socket::ReceiveBytes(char * buffer, const int buffersize);
>
> how should I change it internally?
>
> thanks


I think you're making this a lot more complicated than it need be.
The existing recv() or read() functions provide almost this interface
already. If you want to avoid them blocking when no input is
available, set the socket to nonblocking mode before calling them -
you only need do that once instead of checking before every recv().

Cheers,
Tony
 
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