Re: delimiter for istringstream

"James Kanze" <>
19 Dec 2006 13:06:32 -0500
Z.L. wrote:

Except customized manipulator, is there other simple method in C++ for
this task?

I don't quite get the question: except for the idiomatic simple
method, is there any other simple method? Why don't you want to
use the idiomatic method?

Because I can use strtok() of C to separate the string into substrings
according specified delimiters, I wonder whether more convenient or
simpler method in C++ can handle this task.

Well, you can and you can't. First, of course, there's no way
you can use strtok() on an input stream. Nor will it convert
the doubles for you. And of course, you can't really use it if
you expect the resulting code to be in any way maintainable or

One alternative solution to a custom manipulator (are there any
other kinds that you really use?) is to read line by line, using
getline, and use boost::regex to split the line up into fields,
and then istringstream to convert each field into a double.
It's a bit wordier than the custom manipulator, largely because
you need to pass through the istringstream again, but in many
contexts, it is preferrable, for two reasons:

 -- it provides a convenient resynchronization point in case of
    an error (and in fact, provides better error detection), and

 -- it allows a lot more freedom with regards to how you specify
    fields and their separators.

An alternative to boost::regex for splitting the line into
fields would be my FieldArray classes (in the Text components at; they're probably less
flexible that boost::regex in general, but very work well when
you have an unknown number of fields, with the same separator
between each field. In your case, a
RegularExpressionSeparatedFields would fit the bill nicely, with
"[[:space:]]+|[[:space:]]*:[[:space:]]*" as the regular
expression. (Regretfully, using this class implies installing
and using all of my library, as it depends on a number of other
things in the library.)

James Kanze (GABI Software)
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