Go Printf

Quick reminder

# equivalent of php print_r()
fmt.Printf("%+v\n", r.PostForm)

# In a go template
{{printf "%+v" .Raw}}

fmt.Printf("Type of math.MaxInt is %T\n", math.MaxInt)

Go Printf verbs

General:

    %v	the value in a default format
    %+v	when printing structs, the plus flag adds field names
    %#v	a Go-syntax representation of the value
    %T	a Go-syntax representation of the type of the value
    %%	a literal percent sign; consumes no value

Boolean:

    %t	the word true or false

Integer:

    %b	base 2
    %c	the character represented by the corresponding Unicode code point
    %d	base 10
    %o	base 8
    %q	a single-quoted character literal safely escaped with Go syntax.
    %x	base 16, with lower-case letters for a-f
    %X	base 16, with upper-case letters for A-F
    %U	Unicode format: U+1234; same as "U+%04X"

Floating-point and complex constituents:

    %b	decimalless scientific notation with exponent a power of two,
    	in the manner of strconv.FormatFloat with the 'b' format,
    	e.g. -123456p-78
    %e	scientific notation, e.g. -1.234456e+78
    %E	scientific notation, e.g. -1.234456E+78
    %f	decimal point but no exponent, e.g. 123.456
    %F	synonym for %f
    %g	%e for large exponents, %f otherwise. Precision is discussed below.
    %G	%E for large exponents, %F otherwise

String and slice of bytes (treated equivalently with these verbs):

    %s	the uninterpreted bytes of the string or slice
    %q	a double-quoted string safely escaped with Go syntax
    %x	base 16, lower-case, two characters per byte
    %X	base 16, upper-case, two characters per byte

Pointer:

    %p	base 16 notation, with leading 0x
    The %b, %d, %o, %x and %X verbs also work with pointers,
    formatting the value exactly as if it were an integer.

The default format for %v is:

    bool:                    %t
    int, int8 etc.:          %d
    uint, uint8 etc.:        %d, %#x if printed with %#v
    float32, complex64, etc: %g
    string:                  %s
    chan:                    %p
    pointer:                 %p

For compound objects, the elements are printed using these rules,
recursively, laid out like this:

    struct:             {field0 field1 ...}
    array, slice:       [elem0 elem1 ...]
    maps:               map[key1:value1 key2:value2]
    pointer to above:   &{}, &[], &map[]

Width is specified by an optional decimal number immediately preceding the
verb. If absent, the width is whatever is necessary to represent the value.
Precision is specified after the (optional) width by a period followed by a
decimal number. If no period is present, a default precision is used. A
period with no following number specifies a precision of zero. Examples:

    %f     default width, default precision
    %9f    width 9, default precision
    %.2f   default width, precision 2
    %9.2f  width 9, precision 2
    %9.f   width 9, precision 0

Other flags:

    +	always print a sign for numeric values;
    	guarantee ASCII-only output for %q (%+q)
    -	pad with spaces on the right rather than the left (left-justify the field)
    #	alternate format: add leading 0 for octal (%#o), 0x for hex (%#x);
    	0X for hex (%#X); suppress 0x for %p (%#p);
    	for %q, print a raw (backquoted) string if strconv.CanBackquote
    	returns true;
    	always print a decimal point for %e, %E, %f, %F, %g and %G;
    	do not remove trailing zeros for %g and %G;
    	write e.g. U+0078 'x' if the character is printable for %U (%#U).
    ' '	(space) leave a space for elided sign in numbers (% d);
    	put spaces between bytes printing strings or slices in hex (% x, % X)
    0	pad with leading zeros rather than spaces;
    	for numbers, this moves the padding after the sign

Flags are ignored by verbs that do not expect them. For example there is no
alternate decimal format, so %#d and %d behave identically.