General:
~~~
打印结构体加上字段名
%v the value in a default format
when printing structs, the plus flag (%+v) adds field names
值
%#v a Go-syntax representation of the value
值类型
%T a Go-syntax representation of the type of the value
字面%分号
%% a literal percent sign; consumes no value
~~~
Boolean:
bool类型
`%t the word true or false`
Integer:
~~~
二进制
%b base 2
unicode码表
%c the character represented by the corresponding Unicode code point
10 8进制
%d base 10
%o base 8
%q a single-quoted character literal safely escaped with Go syntax.
16进制，小写和大写字母
%x base 16, with lower-case letters for a-f
%X base 16, with upper-case letters for A-F
Unicode格式
%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
%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 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
Width and precision are measured in units of Unicode code points, that is, runes. (This differs from C's printf where the units are always measured in bytes.) Either or both of the flags may be replaced with the character '*', causing their values to be obtained from the next operand, which must be of type int.
For most values, width is the minimum number of runes to output, padding the formatted form with spaces if necessary.
For strings, byte slices and byte arrays, however, precision limits the length of the input to be formatted (not the size of the output), truncating if necessary. Normally it is measured in runes, but for these types when formatted with the %x or %X format it is measured in bytes.
For floating-point values, width sets the minimum width of the field and precision sets the number of places after the decimal, if appropriate, except that for %g/%G precision sets the total number of significant digits. For example, given 12.345 the format %6.3f prints 12.345 while %.3g prints 12.3. The default precision for %e and %f is 6; for %g it is the smallest number of digits necessary to identify the value uniquely.
For complex numbers, the width and precision apply to the two components independently and the result is parenthesized, so %f applied to 1.2+3.4i produces (1.200000+3.400000i).
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;
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.
For each Printf-like function, there is also a Print function that takes no format and is equivalent to saying %v for every operand. Another variant Println inserts blanks between operands and appends a newline.
Regardless of the verb, if an operand is an interface value, the internal concrete value is used, not the interface itself. Thus:
