How to convert string (containing double max) to double

Question

I have no problem converting "normal" double values, but I can't convert numeric_limits<double>::max() or DBL_MAX string representations?

std::string max = "1.79769313486232e+308";

std::istringstream stream(max);
double value;

// enters here, failbit is set
if (!(stream >> value))

Answer 1

Could it be something like the actual value of DBL_MAX isn't exactly representable in exponential notation with 16 decimal places (say the decimal value is very slightly larger than the two based represenation) but initializing a double with the DBL_MAX will nevertheless set the correct value (due to rounding). std::istringstream may be a little bit more pickish.

EDIT: Actually I found that the value of DBL_MAX in my compiler is 1.7976931348623158e+308 which works fine for me to stream. Your number is rounded and slightly larger, hence the failure.

EDIT2: The exact value of DBL_MAX in decimal form is given by (2 ^ (1023 - 52)) * (2 ^ 53 - 1) which isn't representable with 16 decimal places.

Answer 2

if you use

double v = 1.79769313486232e+308;
cout << v << endl;

it would give you inf. that means the literal number is actually exceeds double now.