Golang : How to control fmt or log print format?


Tags : golang fmt log printf-format

How to control fmt or log print format output? Use this reference as guide on how to control the fmt or log print function format.

Taken from https://golang.org/pkg/fmt/

General:

%v the value in a default format.when printing structs, the plus flag (%+v) 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 - Octal ( see here on leading zero problem )

%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+X"

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. -1234.456e+78

%E scientific notation, e.g. -1234.456E+78

%f decimal point but no exponent, e.g. 123.456

%g whichever of %e or %f produces more compact output

%G whichever of %E or %f produces more compact output

String and slice of bytes:

%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

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);

print a raw (backquoted) string if possible for %q (%#q);

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



Tags : golang fmt log printf-format

By Adam Ng

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