MESSAGE
| DATE | 2010-02-02 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [NYLXS - HANGOUT] C++ Workshop I datatypes cont..
|
On Tue, Feb 02, 2010 at 03:18:52PM -0500, Chris Knadle wrote:
> On Tuesday 02 February 2010 09:33:42 Henning Follmann wrote:
> ...
> > When talking about data types I think it is important for the sake of
> > better coding to use C++ constructs rather than pulling these old c
> > limits.h.
> >
> > C++ data types, unlike java, are implementation dependent. To deal with
> > this the C++ standard provides for the basic data type (short, int, float,
> > double, char, unsigned, long) a standardized interface.
> >
> > numeric_limits is the C++ way to deal with the implementation details
> > of basic types.
>
> That is interesting, as it means you can find out at run-time what the
> underlying size and maximum numbers a variable type can contain, however I
> can't see using this in order to /choose/ a variable type at runtime.
>
It can be useful in the error checking routine of base objects,
especially if it is eithe ran inline function of a macro.
But :) I'm not ready to discuss template syntax just yet ..
Ruben
> I tried doing it anyway as an exercise to see what that would look like.
> So, say I wanted an unsigned variable with exactly 16 bits. Here are two
> implementations.
>
> First what I would normally want to do:
>
>
> #include
> #include
>
> using namespace std;
>
> int main(void)
> {
> uint16_t port_number;
>
> cout << "Sizeof port_number (bytes): " << sizeof(port_number) << endl;
> return 0;
> }
>
>
>
> The second uses dynamic type assignment using a run-time test:
>
>
>
> #include
> #include
>
> using namespace std;
>
> int main(void)
> {
> if (numeric_limits::max() > 65535) {
> cout << "uint too big, using ushort" << endl;
> unsigned short *p = new unsigned short;
> cout << "Size of p is (bytes): " << sizeof(*p) << endl;
> }
> else {
> unsigned int *p = new unsigned int;
> cout << "Size of p is (bytes): " << sizeof(*p) << endl;
> }
>
> cout << "Minimum value for ushort: " <<
> numeric_limits::min() <> cout << "Maximum value for ushort: " <<
> numeric_limits::max() <> cout << "Minimum value for uint: " <<
> numeric_limits::min() <> cout << "Maximum value for uint: " <<
> numeric_limits::max() <>
> return 0;
> }
>
> This gives rise to another more subtle problem with the latter program. One
> is that I haven't used free(), making the program leak memory, but there's
> another: the pointer p only exists within the if{} block due to scope limiting
> in C++. Try to use p outside of the if{} block and you'll get a compiler
> error.
>
> Too messy. I don't think it was meant to be used this way.
>
> -- Chris
>
> --
>
> Chris Knadle
> Chris.Knadle-at-coredump.us
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