Re: Why am I so stupid?
* none:
Every little thing I try to do using STL turns into a five mile crawl
through raw sewage.
I want to use the STL to lex/parse some text. This must have been done
at least 5.0e+75 times before, but I can't find the solution in the FAQ
or in any examples.
This is my utterly failed attempt:
std::string s = "5.0 This is a string";
std::istringstream i(s);
std::cout << "Before: \"" << s << "\"" << std::endl;
float x;
i >> x;
std::cout << "Extracted a float: " << x << std::endl;
std::cout << "After: \"" << s << "\"" << std::endl;
And this is the output produced:
Before: "5.0 This is a string"
Extracted a float: 5
After: "5.0 This is a string"
All that I want in this world is for that output to be, instead, this:
Before: "5.0 This is a string"
Extracted a float: 5
After: " This is a string"
Then I can just continue parsing the remainder of the string.
All you need to do is to continue to read from the istringstream (e.g. if you
really wanted to you could read the remainding text into the string by 'getline(
i, s );', but note that doing that thing repeatedly would yield O(n^2) time).
The stream does not change the original string from which it is initialized.
It just changes its internal buffer read position.
I have
tried the following, and all have failed:
1) Making the assignment "s = i.str();" after the line "i >> x;" in
hopes that "i.str()" would return only the un-extracted portion of the
string. It doesn't. It returns the entire string.
2) Calling "i.sync();" I don't know why I thought this would help. A
shot in the dark.
3) Calling "i.ignore();" a few times. No effect.
4) Changing the last line to:
std::cout << "After: \"" << i << "\"" << std::endl;
(displaying the value of "i" instead of "s". It displays a hex number,
probably a pointer I guess.
5) Changing the last line to:
std::cout << "After: \"" << i.str() << "\"" << std::endl;
I knew before I tried that it wouldn't help, but was desperate.
How do you get the >> operator to actually remove the characters from a
string?
It removes characters from the input buffer. :-)
Help me, Obi Wan. You're my only hope.
P.S.: Please, oh please, don't say Boost. I don't want to add 75000
files to my project just to remove three characters from a string.
Boost isn't a bad idea: it should be there anyway.
The problem with Boost is that, as you rightly note, it's an extreme amount of
baggage for just a small kernel of functionality that you regularly use.
And even though that's about the same as with many other libraries, one does
wish for some "Boost kernel" project...
Cheers & hth.,
- Alf
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