Re: How do I convert and validate numeric data to a string object?

[Thomas Maeder]

Pep <pepaltavista@yahoo.co.uk> writes:

> I have numeric input which I must convert to strings and validate
> whilst doing the conversion. I do not want to mix C functions like
> strtol in to my c++ code, so I'm trying to implement a C++ method
> using examples found in google but none of them work :(

std::strtol() is a Standard C++ function. Where's the problem?


> I have this test program to show my misunderstanding of what is going
> on. It also tests a second problem where I am trying to reset a
> istringstream but need to call the clear() member after the reset,
> which as I misunderstand things is not supposed to be required.
>
> #include <sstream>
> #include <iostream>
>
> long testLong;
> std::string testString;
>
> std::istringstream iss;
>
> iss.exceptions(std::istringstream::eofbit |
> std::istringstream::failbit | std::istringstream::badbit);

This doesn't compile (such a statement is only possible inside a
function definition).

Please post
- real, minimal code (just as much as needed, not more nor less)
- the input you are passing your program
- the output you get
- the output you expect (or hope for)



>
> iss.str(argv[1]);
>
> try
>         // supposedly this will throw exception if conversion is non-
> numeric
> {
>         iss >> testLong;

Side note: This overload of operator>> is declared in the header
<istream>, which you haven't included ...



> }
> catch(std::istringstream::failure& e)
> {
>       std::cout << "caught a exception geezer! [" << e.what() << "]" <<
> std::endl;

... nor <ostream>, where std::endl and this overload of operator<< are
declared.


> So it appears that none of the methods used are capable of doing what
> I require, even though there are hundreds of entries in google that
> state this is the way to do?
>
> What are the "caught a exception geezer! [basic_ios::clear]"
> exceptions about?

They are a big strange; but I am not surprised that the eofbit is set
when parsing an integral number at the end of input.


> So how can I do what I want to do, which is simply to convert and
> validate a numeric input value to a string value?

The code you posted seems to convert from string to numeric, though.