C++Talk.NET

tomwallick@yahoo.com · Guest

I have recently (today) subscribed to your mailing list and I would
like to see if you can assist me in a technical roadblock regarding
std::vector<> initialization within a class (but the vector is static).

I have looked at C++ PL Special Edition, your Effective C++ series,
Lippman's C++ Primer (3rd Edition) and the web and I have not seen a
good (working) snippet of C++ code to perform the following:

I have the following class (interface):

class SignalHandlerBase
{
public:

virtual ~SignalHandlerBase ();
virtual int handleSignal (int signal, siginfo_t* info = 0, void*
context = 0) = 0;
};

Then I have another class (like above details for POSIX signals not
important) named SignalHandler.

class SignalHandler
{
pubic:
//ctor
SignalHandler ();
//dtor
~SignalHandler ();

//Remaining member function declarations omitted for brevity
...
private:

static SignalHandlerBase *signal_handlers_ [NSIG];
};

Scott here is I am stuck.

First of NSIG is defined to be 31 in signal.h or csignal (for C++) .

I would like to use STL vector instead of a C-style array here:

How would I syntantically replace the above version?

Is this correct:

1. std::vector<static SignalHandlerBase*> signal_handlers_; ? (this
one)

or

2. static std::vector<SignalHandlerBase*> signal_handlers_; ? (this
one)

now if it is either 1 or 2 how can I initialize this vector to hold no
more than 31 SignalHandlerBase* slots in memory?

Do I in the encapsulating class constructor call
std::vector<T>::reserve (31),

since I cannot do the following:

//As before
class SignalHandler
{
pubic:
//ctor
SignalHandler ();
//dtor
~SignalHandler ();

//Remaining member function declarations omitted for brevity
...
private:

std::vector<static SignalHandlerBase*> signal_handlers_ (31);
//Is it possible to have a vector of static pointer variables?

or

static std::vector<SignalHandlerBase*> signal_handlers_ (31);
//Or is it possible to have a static vector of non-static pointer
variables?

};

Which of the above is syntactically correct and the correct replacement
for the C-style array declared further up? Based on the correct version
can you show me how to initialize this correct vector replacement BUT
enforcing that the vector can ONLY hold NO MORE than 31 integers
(signals)?

This would be a great help if you can answer this question.

sample code please:

Much help and your help would be greatly appreciated. I certainly do
not mean to take away from your busy time schedule.

Last item:

I read your item in Effective STL about knowing how to pass vector data
and string data to C APIs. I think this is the best item in the book.

I deal alot with Sockets code and have seen a great deal of 3rd party
C++ OS Wrapper Facades for Sockets (ACE, Boost, Common++ etc) they all
seem to have wrapper methods that look like this:

ssize_t send (char buffer [], size_t nbytes);

or

char* find (char pathname []) or char* find (const char pathname [])
where char* or const char* are syntactically replaced with the []
(array versions).

So for:

ssize_t send (char buffer [], size_t nbytes);

can I do this?

ssize_t send (std::vector<char> buffer, size_t nbytes); ?

The above send () call can then call the BSD Sockets ::send call as
follows:

ssize_t NAMESPACE::send (std::vector<char> buffer, size_t nbytes)
{
//delegate to the actual OS Library System call
return ::send (&buffer[0], buffer.size ());
}

I find std::string limiting because I would eventuall call
std::string::c_str () to get the underlying C-style const string which
cannot be passed to API libraries expecting char* - I get the illegal
'error when convering const char* to char*'

It seems that std::vector<char> is more versatile for than std::string
since it can produce a pointer to char (char*) or be casted to const
char*.

std::strings when ::c_str ()'d only produce the const char*.

Thank you,

Tom Wallick

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Thomas Maeder · Guest

[I'm not Scott, but I'm accessing this newsgroup right now Smile

]

"tomwallick (AT) yahoo (DOT) com" <tomwallick (AT) yahoo (DOT) com> writes:

Guest

Well, at the first glance, I would like to first know why do you want
to do it this way.

First, vector is not a C++ replacement for arrays. vector is a STL
container - that provides similar behavior and methods - its a
template! it is a generic way of sharing code (behavior) with type
safety.

Second, templates would be very expensive (time complexity) in your
case - especially if you are dealing with signal handlers and would
like to iterate through the collection. [] operator on vector is
overloaded and is _not_ as simple as C's [] resolution. If you use
e1[e2], in C, it is deferenced as *(e1 + e1). This is the reason why
3[a] is similar to a[3] and is also a legitimate syntax in C.

It is also not guarenteed that vector elements will be stored in
contiguosly in memory. it completely depends on the compiler you are
using. VC++ for example uses one chunk in memory and stores them in
sequence, where as it is not the case on some Unix platforms.

Next question is that In case of your SignalHandler which contains
SignalHandlerBase pointers, are you going to have multiple instances of
SignalHandler objects in your system? If no, then you might want to
consider making it singleton.

For your send() question too - vector is not an array! you cant safely
cast it to char*

Another question: why do you want an array? if you want to have a
signal handler object for a signal, wouldn't hashtable be a more
logical ?

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[ comp.lang.c++.moderated. First time posters: Do this! ]

Andrew Koenig · Guest

<tomwallick (AT) yahoo (DOT) com> wrote in message
news:1139163425.602473.116390 (AT) g47g2000cwa (DOT) googlegroups.com...

Francis Glassborow · Guest

In article <1139267207.613629.218540 (AT) f14g2000cwb (DOT) googlegroups.com>,
ydkulkarni (AT) gmail (DOT) com writes

James Hopkin · Guest

ydkulkarni (AT) gmail (DOT) com wrote:

kanze · Guest

ydkulkarni (AT) gmail (DOT) com wrote:

Attila Feher · Guest

tomwallick (AT) yahoo (DOT) com wrote:
[SNIP]