Subject: Re: [Boost-users] [conversion] Using Lexical_cast to convert string to float
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-06-09 23:17:25
AMDG
Ryan McConnehey wrote:
> In writing some unit tests to convert strings to floats I've come
> across a puzzling situation. I was trying to test that a
> std::bad_cast was thrown if a number was too large to fit into a
> float. The error wasn't thrown but the float was given 1.#INF000.
> The work around I used was to cast to a double and then do a
> numeric_cast on the result. This provided an exception for values
> larger than could fit in a float. Lexical_cast on a double though
> works as I would have expected. If a value is too large to fit into a
> double then a std::bad_cast is called.
>
> float test =
> boost::lexical_cast<float>("3.4e050");
> //test will have the value of 1.#INF000
> float test = boost::numeric_cast<float>(
> boost::lexical_cast<double>("3.4e50"); //std::bad_cast is thrown
> double test = boost::lexical_cast<double>("3.4e350");
> //std::bad_cast is thrown
>
> Is the lexical_cast for float behaving correctly?
The problem is in the standard library. (Tested with msvc 9.0
express--gcc 4.3.0 behaves sensibly).
#include <iostream>
#include <sstream>
int main() {
{
std::istringstream ss("3.4e050");
float val;
ss >> val;
std::cout << std::boolalpha << "ss: " << static_cast<bool>(ss)
<< ", val: " << val << std::endl;
}
{
std::istringstream ss("3.4e350");
double val;
ss >> val;
std::cout << std::boolalpha << "ss: " << static_cast<bool>(ss)
<< ", val: " << val << std::endl;
}
}
ss: true, val: 1.#INF
ss: false, val: -9.25596e+061
In Christ,
Steven Watanabe