Number extraction from a string such as an integer or double

Question

I am having a difficult time thinking of a way to extract a number such as an int or a double from a string extracted from the getline() function.

//Example:

string data = "";
fstream inFile;

//File contains:

"Hello today is 83.3 degrees Fahrenheit."

// use the getline function

getline(inFile, data);

// extract number from string data

Thank You

Do you have access to C++11 or boost (both of which contain regular expressions)? — Micha Wiedenmann, Mar 10 '13 at 23:32

score 0 · Answer 1 · edited May 23 '17 at 12:25

0

You may do the following

getline(inFile, data);

std::istringstream iss;
iss.exceptions(std::istream::failbit | std::istream::badbit );

iss.str(data);
double dTemp = 0;

while( iss.good() ){

  try{
   iss >> dTemp;
   }      
  catch(std::istream::failure &e ){
   /* Do your error check over here */
  }

}

You make also want to read more about C++. Check this link

Hope this helps.

edited May 23 '17 at 12:25

Community

1
1

answered Mar 10 '13 at 23:41

Hrushikesh Kulkarni

301
2
5

That will totally fail as the first thing in OP's string is not the number, but a few random words. – us2012 Mar 10 '13 at 23:44
Thanks, I agree with you. We also need to check the failbit and badbit. – Hrushikesh Kulkarni Mar 10 '13 at 23:47

ed_me · Answer 2 · 2013-03-11T00:51:32.893

You can use sscanf if you are prepared to include cstdio.

The following man pages link will help you:-

http://linux.die.net/man/3/sscanf

Example

char foo[] = "foo bar 12 baz";
int qux;
sscanf(foo, "foo bar %d baz", &qux); 
// qux will be assigned 12

or

char foo[] = "foo bar 12.5 baz";
double qux;
sscanf(foo, "foo bar %lf baz", &qux); 
// qux will be assigned 12.5

You will obviously need to tailor this to your scenario and take various safety issues into consideration.

Number extraction from a string such as an integer or double

2 Answers2