[Tutorial] Extracting data from a string

[wtd]

The standard stream classes we use for dealing with classes have well known capabilities to extract data (integers, floating-point numbers, etc.).

code:

#include <iostream> int main() {    int i;    double d;    std::cin >> i >> d;    return 0; }

But what if you want to perform a similar operation on a string?

The istringstream class allows that very thing.

code:

#include <string> #include <sstream> #include <iostream> int main() {         int i;         double d;         std::string str = "32 42.67";         std::istringstream input(str);         input >> i >> d;         return 0; }

Additionally, it's possible to check for errors with this class.

code:

#include <string> #include <sstream> #include <iostream> int main() {         double d;         std::string str = "hello";         std::istringstream input(str);         input >> d;         if (input.fail())         {                 std::cerr << "Couldn't extract a double." <<std::endl;         }         return 0; }

[Andy]

very very cool

+10 bits

[Mazer]

Well... wow. When I was reading this in the morning, I was too tired to know what was going on. But wow, this is quite slick.

[Andy]

who needs throw and catch when u have this 8)

[rizzix]

yea dodge u need to learn a lot.

[Andy]

o psh, u java mod, get out of my c++ world lol

[wtd]

Exceptions are still very useful.

The method I posted, and the error-checking I demonstrated, is an improvement on the methods one would use to do the same in C (in many many ways). This doesn't mean there's not room for improvement.

[Andy]

i noe they are still useful.. im just glad that there is a niceway of doing it without exceptions in c++

[wtd]

Going into pedantic mode for a moment:

What I demonstrated was C++ code. C is a different programming language. The two are not interchangeable.

[Andy]

you have no proof.. o crap.. it says edited by dodge.. damit

[wtd]

I should have quoted you.

[Andy]

lol incase you havent noticed, i have c++ powers... and i can edit ur posts lol

[Geminias]

hey wtd, if you try to input a string manually with:

"std::cin >> str;"

I found that it doesn't extract. Can you explain why this is? And what might be a suitable alternative to initializing the str at runtime?

[wtd]

Be aware that if you do that, the string it reads will only be upto the first space, by default.

If, for instance, the user types "hello world foo bar", "str" will only contain "hello". You would need to use std::getline to read an entire line of input.