MESSAGE
| DATE | 2010-02-02 |
| FROM | Ruben Safir
|
| SUBJECT | Subject: [NYLXS - HANGOUT] C++ Workshop I datatypes cont..
|
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.
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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