What Is the Java Equivalent of Sscanf for Parsing Values from a String Using a Known Pattern

what is the Java equivalent of sscanf for parsing values from a string using a known pattern?

The problem is Java hasn't out parameters (or passing by reference) as C or C#.

But there is a better way (and more solid). Use regular expressions:

Pattern p = Pattern.compile("(\\d+)-(\\p{Alpha}+)-(\\d+) (\\d+)\\.(\\d+)\\.(\\d+)\\.(\\d+)")
Matcher m = p.matcher("17-MAR-11 15.52.25.000000000");
day = m.group(1);
month= m.group(2);
....

Of course C code is more concise, but this technique has one profit:
Patterns specifies format more precise than '%s' and '%d'. So you can use \d{2} to specify that day MUST be compose of exactly 2 digits.

sscanf equivalent in Java

Scanner scanner = new Scanner ("2 A text 3 4");
scanner.nextInt (); // 2
scanner.next ();    // A 
scanner.next ();    // text
scanner.nextInt (); // 3
scanner.nextInt (); // 4
// and so on.

Here is the official documentation of the Scanner class.

Is there an equivalent method to C's scanf in Java?

Take a look at this site, it explains two methods for reading from console in java, using Scanner or the classical InputStreamReader from System.in.

Following code is taken from cited website:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class ReadConsoleSystem {
  public static void main(String[] args) {

    System.out.println("Enter something here : ");

    try{
        BufferedReader bufferRead = new BufferedReader(new InputStreamReader(System.in));
        String s = bufferRead.readLine();

        System.out.println(s);
    }
    catch(IOException e)
    {
        e.printStackTrace();
    }

  }
}

--

import java.util.Scanner;

public class ReadConsoleScanner {
  public static void main(String[] args) {

      System.out.println("Enter something here : ");

       String sWhatever;

       Scanner scanIn = new Scanner(System.in);
       sWhatever = scanIn.nextLine();

       scanIn.close();            
       System.out.println(sWhatever);
  }
}

Regards.

Elegant equivalent to C's vsscanf() in Java

You can use java.text.MessageFormat. For example:

public static void main(String[] args) throws ParseException {
    String input="hello 1:2.3.4";
    MessageFormat form = new MessageFormat("{0} {1,number}:{2,number,integer}.{3,number}");
    Object[] data = form.parse(input);
    for(Object o : data) {
        System.out.println(o.getClass()+" : "+o.toString());
    }
}

Which produces the output:

class java.lang.String : hello
class java.lang.Long : 1
class java.lang.Long : 2
class java.lang.Double : 3.4

Of course, the format isn't as compact as that used by scanf, but it is out of the box Java.

Reading from a txt file in Java

if(scan.hasNextDouble())
{
    price = scan.nextDouble();
}

change this to

 price = Double.parseDouble(scan.next().substring(1));

And change

 System.out.println(name + " " + quantity + " " + item_name + " " +    price);

this to

 System.out.println(name + " " + quantity + " " + item_name + " $" +    price);

How sscanf() splits a string in C

This explanation is little over-simplified and there is more than this going on inside the sscanf as the source code is itself more than 3,000 lines of code.

The format specifier mentioned by you in the example is listed below with their corresponding match pattern

%d : [0-9],[-,+]

%f : [0-9],[-,+,.]

%c : [a-z],[A-Z], Other ASCII Characters

Parsing

1. First, for %d, it will first search for [+,-] signs, and if not found then it will look for [0-9] single digits in sequence. As soon as it sees a non-single digit (A = 65) in the string, it will end its search for %d and save the value of the int to the corresponding address passed to sscanf.
2. Second, for %c, now it will take the next format specifier passed i.e. %c and begin again from the location where it previously stopped. This time it just has to read a single byte from the string and save it to the corresponding address passed to sscanf
3. Third, for %f, it will first search for [+,-] signs, and if not found it will then look for . and the single digits [0-9]. This continues until it gets something which is not part of the %f, which in this case will be \0. And save it to the corresponding address passed to sscanf

Finally, once everything is completed and the string is split, it returns the total number of arguments parsed. So, it a good programming practice to compare the number of the passed argument list with the returned value.

Reference:

1. sscanf source code
2. vfscanf source code

---

Related Topics