I am currently using the following code to convert a string (or part of it) into an integer:
This code will put the integer value into temp. It will also disregard any alpha characters after the int.Code:string myString; ...... int temp = 0; sscanf(myString.c_str(), "%d", &temp);
I realise that this is a bit of a mix of C and C++. Is there a better way to do this in C++? Or do I need to convert it to a C string first??
Thanks
Mark
If you want to allow trailing whitespace, but not characters or more numbers or a floatingCode:std::istringstream iss(myString); int n; if(iss >> n && iss.eof()) { // myString is a properly formated number with no trailing characters or whitespace // leading whitespace is ignored } else { iss.clear(); // allows us to work with the string again. iss.get(); // is the character that goofed things up. iss.tellg(); // is the position in the string of the offending character. }
point number you could use
Code:if(iss >> n >> std::ws && iss.eof()) ...
There's this entry in the FAQ
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
the easiest way to convert a std::string to int is STILL using the C atoi() function. Sometimes C is still the best -- even though atoi() does not check for integer overflow.
Now isn't that a whole lot simpler than all that stringstream crap posted previously?Code:std::string str = "123"; int n; n = atoi(str.c_str());
Last edited by Ancient Dragon; 01-18-2006 at 10:42 AM.
Personally, I prefer the stringstream crap posted by laserlight in the FAQ.
Last edited by treenef; 01-18-2006 at 03:58 PM.
what you want is boost::lexical_cast
simple and elegant, but also typesafe and extensible.
The price you pay for this is a small decrease in performance, but if converting strings to ints is your bottleneck, you've got bigger things to worry aboutCode:std::string aString = "123"; int val = boost::lexical_cast<int>(aString);
"I saw a sign that said 'Drink Canada Dry', so I started"
-- Brendan Behan
Free Compiler: Visual C++ 2005 Express
If you program in C++, you need Boost. You should also know how to use the Standard Library (STL). Want to make games? After reading this, I don't like WxWidgets anymore.Want to add some scripting to your App?
Aren't sstream and atoi both faster than the booth method? And don't they also both have cleaner syntax? And, er, don't they also not require you to use boost, which... isn't really standard?
Probably, no and yes, and yes. But lexical_cast is "simple and elegant, but also typesafe and extensible," which cannot be said for the other two choices. Most Boost libraries are also portable and tested thoroughly just like standard libraries, so much that many are being added to the standard.
There are many reasons to use boost in your app, and if you are using it already, then lexical_cast is an excellent solution to the conversion problem.
atoi is faster. sstream, not noticeably. See these benchmarks:
http://www.gotw.ca/publications/mill19.htm
(Note that these are old and outdated - more up-to-date benchmarks could be interesting, as C++ standard libraries tend to get better.)
stringstream cleaner syntax than lexical_cast? Are you kidding?And don't they also both have cleaner syntax?
Actually, I prefer the very clear lexical_cast even over the cryptic acronym "atoi".
So? Boost is freely available, usable without charge or limitation for both commercial and non-commercial projects, compatible with the GPL, extremely widely used, tested, peer-reviewed and documented, maintained by a group of people many of whom are on the C++ standards committee, work on most compilers out there (lexical_cast in particular), ... what more do you want?And, er, don't they also not require you to use boost, which... isn't really standard?
Last edited by CornedBee; 01-18-2006 at 07:13 PM.
All the buzzt!
CornedBee
"There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
- Flon's Law
in short, "b00s7 pwns u"
It rules. I honestly think I'd cry if someone made me go back to programming C++ without boost.bind and boost.lambda. And don't get me started on the smart pointers...
"I saw a sign that said 'Drink Canada Dry', so I started"
-- Brendan Behan
Free Compiler: Visual C++ 2005 Express
If you program in C++, you need Boost. You should also know how to use the Standard Library (STL). Want to make games? After reading this, I don't like WxWidgets anymore.
IMO I don't think you can reply completely on either, stringstream, atoi or boost functions.This code will put the integer value into temp. It will also disregard any alpha characters after the int.
Take for example stringstream.
Let's say you ask the user to type in a number at the command line, and by accident they enter:
Ok, that's not going to be a problem since stringstream would truncate the input to 1234 ignoring the alphanumeric input.Code:1234bd
However, what happens if they type:
And the only mistake was they hit 'b' by accident.Code:1234b3432
Stringstream will just assume they meant to type 1234 and ignore all the rest.Clearly in this example there is a sense of ambiguity.
Sometimes when you are writing a parser you have to ensure you go through all the specific cases that may throw up errors.
I mean when I was writing my univarte equation solver,relying solely on stringstream or boost would have not worked. Boost is an excellent resource, however, sometimes you have to do it the hard way and ensure every exception is accounted for.
Garbage In = Garbage outHowever, what happens if they type:
Code:
1234b3432
I don't see the problem, check your input first, then call your preference of conversion
