Format Specifiers in Julia

Format Specifiers are used to format the Input and Output of a Programming language. It tell the compiler about the data type of the Input that is being passed to it. Julia contains a package Printf and using its macro @printf takes input string value to be formatted and accepts parameters as variables to apply to the string.
@printf is a macro in Julia, which has the following syntax:

@printf([io::IOstream], "%Fmt", args...)

Space format specifier 

It is used to print a space before the variable value over which it is specified. The variable value can belong to any data type, numeric, or strings. 

# declaring a variable string  
val = "Space"

# importing module
using Printf

# adding space identifier after a string “Added” 
@printf("Added, % s \n", val)

Output:

Added, Space 

+ sign format specifier

On specifying a numeric value as argument with the %+d format, '+' sign is added before it. On specifying floating-point number as argument only the part before decimal is returned as output with +ve sign. 

# declaring numeric value 
num1 = 111

# importing required module
using Printf

# adding positive sign before numerical value
@printf("Adding %+d", num1)

# declaring floating point number
num2 = 10.1

# adding positive sign before floating number
@printf("Adding positive sign %+d", num2)

Output:

+111
+11

The floating numbers are converted to integers with a positive sign.

Left Justification (-) specifier

The output returned can be explicitly left-justified by applying a minus sign after the symbol %. The following code, for example, % 16.4f justifies the passed parameter in a field of 16 characters with two decimal places. 

# importing module
using Printf

# declaring a floating point number
num1 = 10.1234

# left justifying the number 
@printf("|%-16.4f|", num1)

Output:

|10.1234         |

%% format specifier

This format specifier can be used to insert a % sign. There are no parameters specified explicitly. It can be used for both strings or numbers. 

# importing module
using Printf

# embedded in numerical values
@printf("2 %% 8 = 0")

# embedding in strings 
@printf("hello %% gfg ")

Output:

2 % 8 = 0
hello % gfg

%x %X format specifier 

This representation is used to donate a hexadecimal number of the specified numeric value in either lower case or upper case characters %x in lower case and %X in upper case. Only numerical values can be specified as parameters in this argument list. 

# importing module
using Printf

# converting 100 to lower case hexadecimal
@printf("% x", 100)

# converting 13 to lower case hexadecimal
@printf("% x", 13)

# converting 234 to upper case hexadecimal
@printf("% X", 234)

Output:

64
d
EA

%o format specifier 

This representation is used to denote the number specified as the argument in the octal form. The variable to be converted cannot be a floating-point number. 

# importing module
using Printf

# converting 372 from decimal 
# to octal representation
@printf("% o", 372)

# converting 9 to octal
@printf("% o", 9)

Output:

564
11

%e %E format specifier

This format specifier is used to express the value in a scientific way with %E expressing the output in upper case characters and %e in lower case characters. 

using Printf

# converting numerical and floating numbers
# scientific notation in lower case
@printf("% e", 100)
@printf("% e", 12.56)

# converting numerical and floating numbers
#  scientific notation in upper case
@printf("% E", 100)
@printf("% E", 99.78)

Output:

1.000000e+02
1.256000e+01
1.000000E+02
9.978000E+01

%f format specifier

Used to convert a number into floating-point integer values. Works both the numerical and decimal point numbers. It appends exactly 6 digits after the decimal, by default. We can specify the number of digits in %.xf parameter, where x indicates the number of digits. 
 

using Printf

# converting numerical to decimal point
@printf("% f", 100)

# converting floating to decimal point
@printf("% f", 12.56)

# printing decimal number upto 4 places only
@printf("%.4f", 12.56)

Output:

100.000000
12.560000
12.5600