Double.parseDouble() equivalent in C++? [duplicate]

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Closed 8 years ago.

Possible Duplicate:
std::string to float or double

I am writing a calculator (learning C++), and just decided to make a calculator, since that was the first thing I did when learning Java.

The program does the following:

1. Asks the user for the first number
2. Asks what the user wants to do with the number (-,+,*,/)
3. Asks for the second number
4. Displays the result.

when grabbing a number from the user in Java I used Double.parseDouble(number) to check if what they entered is a number or not.

Is there a similar command in C++? Ive been doing research and it seems like you have to use tricks such as comparing it to ASCII equivalents etc.. basically a ton of code for a simple task... so before i take that route, I wanted to stop by here and see if perhaps there is some sort of call I can make to check if the input is a number. I need it to validate negatives, zero and positives, as well as numbers with decimals... everything else should be rejected and the user should be asked for input again.

When I did it in Java I used try/catch statement and if the input was invalid it would return the method (in other words, itself) so it would loop and ask the user for input again.

Thanks!

Answer 1

You can use strtod. It handles underflow and out of range values in a convenient way.

Additionally, as Joachim Pileborg notes, if you use C++11 compliant compiler, there is std::stod in the standard library.

Answer 2

Use the function double atof(const char*) ;

example usage:

const char* = "3.14159";
double pi = atof(myDouble);

Answer 3

How about using isdigit function.