what do these symbolic strings mean: %02d %01d ?

Question

I'm looking at a code line similar to:

sprintf(buffer,"%02d:%02d:%02d",hour,minute,second);

I think the symbolic strings refer to the number of numeric characters displayed per hour, minute etc - or something like that, I am not entirely certain.

Normally I can figure this sort of thing out but I have been unable to find any useful reference searching "%02d %01d" on google. Anyone able to shed some light on this for me?

Answer 1

http://www.cplusplus.com/reference/clibrary/cstdio/printf/

the same rules should apply to Java.

in your case it means output of integer values in 2 or more digits, the first being zero if number less than 9

Answer 2

The answer from Alexander refers to complete docs...

Your simple example from the question simply prints out these values with 2 digits - appending leading 0 if necessary.

Answer 3

Instead of Googling for %02d you should have been searching for sprintf() function.

%02d means "format the integer with 2 digits, left padding it with zeroes", so:

Format  Data   Result
%02d    1      01
%02d    11     11

Answer 4

http://en.wikipedia.org/wiki/Printf#printf_format_placeholders

The article is about the class of printf functions, in several languages, from the 50s to this day.

Answer 5

The Java equivalent for the sprintf() function is [String.format()][1] which returns a string having applied the provided formatter string and its values.

String buffer = String.format("%02d:%02d:%02d",hour,minute,second);

[1]: http://download-llnw.oracle.com/javase/1.5.0/docs/api/java/lang/String.html#format(java.lang.String, java.lang.Object...)

Answer 6

They are formatting String. The Java specific syntax is given in java.util.Formatter.

The general syntax is as follows:

   %[argument_index$][flags][width][.precision]conversion

%02d performs decimal integer conversion d, formatted with zero padding (0 flag), with width 2. Thus, an int argument whose value is say 7, will be formatted into "07" as a String.

You may also see this formatting string in e.g. String.format.

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Commonly used formats

These are just some commonly used formats and doesn't cover the syntax exhaustively.

Zero padding for numbers

System.out.printf("Agent %03d to the rescue!", 7);
// Agent 007 to the rescue!

Width for justification

You can use the - flag for left justification; otherwise it'll be right justification.

for (Map.Entry<Object,Object> prop : System.getProperties().entrySet()) {
    System.out.printf("%-30s : %50s%n", prop.getKey(), prop.getValue());
}

This prints something like:

java.version                   :                                 1.6.0_07
java.vm.name                   :               Java HotSpot(TM) Client VM
java.vm.vendor                 :                    Sun Microsystems Inc.
java.vm.specification.name     :       Java Virtual Machine Specification
java.runtime.name              :          Java(TM) SE Runtime Environment
java.vendor.url                :                     http://java.sun.com/

For more powerful message formatting, you can use java.text.MessageFormat. %n is the newline conversion (see below).

Hexadecimal conversion

System.out.println(Integer.toHexString(255));
// ff

System.out.printf("%d is %<08X", 255);
// 255 is 000000FF

Note that this also uses the < relative indexing (see below).

Floating point formatting

System.out.printf("%+,010.2f%n", 1234.567);
System.out.printf("%+,010.2f%n", -66.6666);
// +01,234.57
// -000066.67

For more powerful floating point formatting, use DecimalFormat instead.

%n for platform-specific line separator

System.out.printf("%s,%n%s%n", "Hello", "World");
// Hello,
// World

%% for an actual %-sign

System.out.printf("It's %s%% guaranteed!", 99.99);
// It's 99.99% guaranteed!

Note that the double literal 99.99 is autoboxed to Double, on which a string conversion using toString() is defined.

n$ for explicit argument indexing

System.out.printf("%1$s! %1$s %2$s! %1$s %2$s %3$s!",
    "Du", "hast", "mich"
);
// Du! Du hast! Du hast mich!

< for relative indexing

System.out.format("%s?! %<S?!?!?", "Who's your daddy");
// Who's your daddy?! WHO'S YOUR DADDY?!?!?

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