C++Talk.NET

Guest

I need a conversion function that converts values from string to a
particular type. For this I have a template function that looks like
this ...

template<class T>
T value(const string& s)
{
istringstream(s);
T val;
is >> val;
return val;
}

Now for double type the lowest positive value is 2.22507-308 and I get
different answers when I use this function vs atof() function. I am not
getting the reason here. Interestingly, if I reduce the exponent value
from -308 to -307, I get similar results.

Regards,
Harry.

Guest

Forgot to mention this before. atof() behaviour is expected for -308
exp and that of istringstream is wrong.

Regards,
Harry.

sharmaharish (AT) gmail (DOT) com wrote:

Guest

mlimber,

I tried compiling the same program with a later ver of MS C/C++
compiler, which is ...
Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.42
for 80x86

With this compiler the test program gives expected results. But the GCC
compiler that I am using is gcc version 3.3.1 (mingw special
20030804-1), and it still gives out garbage. And by the way I believe,
there is no garbage i/p in the test program and hence there is no
question of GIGO. Moreover, I don't think there is any need of
exception handling in the test code with the given valid input and I
don't understand how that extra piece of error checking will help. If
your compiler/lib gives you expected results with the given input, it
should behave the same without that as well.

Another simple test to confirm the problem is,

int main() { double d; cin >> d; cout << d; return 0; }

Just enter the value 2.22507-308 after compiling with your compiler and
it should show the expected result. But if you try this with the GCC
compiler version that I have mentioned, it gives out garbage. This
piece of code behaves similar to the earlier test program with both the
compilers that I used.

Lastly I tried your changes with GCC and it generates exception and
that tells me that there is some definite issue in the related version
of c++ lib that it is using.

Regards,
Harish Sharma

Guest

sharmaharish (AT) gmail (DOT) com wrote: