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boost::lexical_cast seems not not be consistent given different
inputs. E.g. std::complex is stringified like iostream, but float and
double avoid scientific notation… mostly. See below for comparisons
between before and after (`printf` is what this commit switches to).
I don't think the differences matter.
```
int main() {
constexpr float low_float = 200000000.2;
constexpr float high_float = 20000000000.2;
constexpr float low_double = 200000000.2;
constexpr float mid_double = 20000000000.2;
constexpr float high_double = 200000000000000000.2;
const std::complex<float> c(1.3,low_float);
const std::complex<double> d(1.3,low_double);
const std::complex<double> d2(1.3,high_double);
const std::vector<float> fs = {low_float, high_float};
const std::vector<double> ds = {low_double, mid_double, high_double};
std::cout << "# complex\n";
std::cout << "iostream: " << c << std::endl;
std::cout << "lexical_cast: " << boost::lexical_cast<std::string>(c) << std::endl;
std::cout << std::endl;
for (int i = 0; i < fs.size(); i++) {
std::cout << "# float " << i << std::endl;
std::cout << "iostream: " << fs[i] << std::endl;
std::cout << "to_string: " << std::to_string(fs[i]) << std::endl;
printf("printf %.f\n", std::numeric_limits<float>::digits10, fs[i]);
std::cout << "lexical: " << boost::lexical_cast<std::string, float>(fs[i]) << std::endl;
std::cout << std::endl;
}
for (int i = 0; i < ds.size(); i++) {
std::cout << "# double " << i << std::endl;
std::cout << "iostream: " << ds[i] << std::endl;
std::cout << "to_string: " << std::to_string(ds[i]) << std::endl;
printf("printf %.*g\n", std::numeric_limits<double>::digits10, ds[i]);
std::cout << "lexical: " << boost::lexical_cast<std::string, double>(ds[i]) << std::endl;
std::cout << std::endl;
}
}
```
Output (Debian amd64):
```
iostream: (1.3,2e+08)
lexical_cast: (1.3,2e+08)
iostream: 2e+08
to_string: 200000000.000000
printf 200000000
lexical: 200000000
iostream: 2e+10
to_string: 20000000000.000000
printf 20000000000
lexical: 2e+10
iostream: 2e+08
to_string: 200000000.000000
printf 200000000
lexical: 200000000
iostream: 2e+10
to_string: 20000000000.000000
printf 20000000000
lexical: 20000000000
iostream: 2e+17
to_string: 199999996861349888.000000
printf 1.9999999686135e+17
lexical: 1.9999999686134989e+17
```
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