Golang基础（一）

常用参数解释

• 在命令行中可以通过 go help 命令来查看go参数如下：

Go is a tool for managing Go source code.

Usage:

        go command [arguments]

The commands are:

        build       compile packages and dependencies
        clean       remove object files
        doc         show documentation for package or symbol
        env         print Go environment information
        bug         start a bug report
        fix         run go tool fix on packages
        fmt         run gofmt on package sources
        generate    generate Go files by processing source
        get         download and install packages and dependencies
        install     compile and install packages and dependencies
        list        list packages
        run         compile and run Go program
        test        test packages
        tool        run specified go tool
        version     print Go version
        vet         run go tool vet on packages

Use "go help [command]" for more information about a command.

Additional help topics:

        c           calling between Go and C
        buildmode   description of build modes
        filetype    file types
        gopath      GOPATH environment variable
        environment environment variables
        importpath  import path syntax
        packages    description of package lists
        testflag    description of testing flags
        testfunc    description of testing functions

Use "go help [topic]" for more information about that topic.

• 解释

  go version 查看go语言版本

  go env 查看go语言环境详情

  go list 查看go语言文件目录

  go build 把源码文件构建成可执行的系统文件

  go clean 清空当前生成的可执行文件

  go vet 静态解析文件，检查是否有语法错误

  go get 从远程下载第三方go语言库

  go bug 提交bug

  go test 测试

  go run 运行go文件

go语言的自省机制

• 可以通过help来查看go的参数。

• 可以通过 godoc + 包名 的方式来查看包的源码

  • 比如

  C:\Users\Administrator>godoc fmt
  use 'godoc cmd/fmt' for documentation on the fmt command
  
  PACKAGE DOCUMENTATION
  
  package fmt
      import "fmt"
  
      Package fmt implements formatted I/O with functions analogous to C's
      printf and scanf. The format 'verbs' are derived from C's but are
      simpler.
  
  
      Printing
  
      The verbs:
  
      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
          %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 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, %f and %#g 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;
                  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.
  
      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:
  
          var i interface{} = 23
          fmt.Printf("%v\n", i)
  
      will print 23.
  
      Except when printed using the verbs %T and %p, special formatting
      considerations apply for operands that implement certain interfaces. In
      order of application:
  
      1. If the operand is a reflect.Value, the operand is replaced by the
      concrete value that it holds, and printing continues with the next rule.
  
      2. If an operand implements the Formatter interface, it will be invoked.
      Formatter provides fine control of formatting.
  
      3. If the %v verb is used with the # flag (%#v) and the operand
      implements the GoStringer interface, that will be invoked.
  
      If the format (which is implicitly %v for Println etc.) is valid for a
      string (%s %q %v %x %X), the following two rules apply:
  
      4. If an operand implements the error interface, the Error method will
      be invoked to convert the object to a string, which will then be
      formatted as required by the verb (if any).
  
      5. If an operand implements method String() string, that method will be
      invoked to convert the object to a string, which will then be formatted
      as required by the verb (if any).
  
      For compound operands such as slices and structs, the format applies to
      the elements of each operand, recursively, not to the operand as a
      whole. Thus %q will quote each element of a slice of strings, and %6.2f
      will control formatting for each element of a floating-point array.
  
      However, when printing a byte slice with a string-like verb (%s %q %x
      %X), it is treated identically to a string, as a single item.
  
      To avoid recursion in cases such as
  
          type X string
          func (x X) String() string { return Sprintf("<%s>", x) }
  
      convert the value before recurring:
  
          func (x X) String() string { return Sprintf("<%s>", string(x)) }
  
      Infinite recursion can also be triggered by self-referential data
      structures, such as a slice that contains itself as an element, if that
      type has a String method. Such pathologies are rare, however, and the
      package does not protect against them.
  
      When printing a struct, fmt cannot and therefore does not invoke
      formatting methods such as Error or String on unexported fields.
  
      Explicit argument indexes:
  
      In Printf, Sprintf, and Fprintf, the default behavior is for each
      formatting verb to format successive arguments passed in the call.
      However, the notation [n] immediately before the verb indicates that the
      nth one-indexed argument is to be formatted instead. The same notation
      before a '*' for a width or precision selects the argument index holding
      the value. After processing a bracketed expression [n], subsequent verbs
      will use arguments n+1, n+2, etc. unless otherwise directed.
  
      For example,
  
          fmt.Sprintf("%[2]d %[1]d\n", 11, 22)
  
      will yield "22 11", while
  
          fmt.Sprintf("%[3]*.[2]*[1]f", 12.0, 2, 6)
  
      equivalent to
  
          fmt.Sprintf("%6.2f", 12.0)
  
      will yield " 12.00". Because an explicit index affects subsequent verbs,
      this notation can be used to print the same values multiple times by
      resetting the index for the first argument to be repeated:
  
          fmt.Sprintf("%d %d %#[1]x %#x", 16, 17)
  
      will yield "16 17 0x10 0x11".
  
      Format errors:
  
      If an invalid argument is given for a verb, such as providing a string
      to %d, the generated string will contain a description of the problem,
      as in these examples:
  
          Wrong type or unknown verb: %!verb(type=value)
                  Printf("%d", hi):          %!d(string=hi)
          Too many arguments: %!(EXTRA type=value)
                  Printf("hi", "guys"):      hi%!(EXTRA string=guys)
          Too few arguments: %!verb(MISSING)
                  Printf("hi%d"):            hi%!d(MISSING)
          Non-int for width or precision: %!(BADWIDTH) or %!(BADPREC)
                  Printf("%*s", 4.5, "hi"):  %!(BADWIDTH)hi
                  Printf("%.*s", 4.5, "hi"): %!(BADPREC)hi
          Invalid or invalid use of argument index: %!(BADINDEX)
                  Printf("%*[2]d", 7):       %!d(BADINDEX)
                  Printf("%.[2]d", 7):       %!d(BADINDEX)
  
      All errors begin with the string "%!" followed sometimes by a single
      character (the verb) and end with a parenthesized description.
  
      If an Error or String method triggers a panic when called by a print
      routine, the fmt package reformats the error message from the panic,
      decorating it with an indication that it came through the fmt package.
      For example, if a String method calls panic("bad"), the resulting
      formatted message will look like
  
          %!s(PANIC=bad)
  
      The %!s just shows the print verb in use when the failure occurred. If
      the panic is caused by a nil receiver to an Error or String method,
      however, the output is the undecorated string, "<nil>".
  
  
      Scanning
  
      An analogous set of functions scans formatted text to yield values.
      Scan, Scanf and Scanln read from os.Stdin; Fscan, Fscanf and Fscanln
      read from a specified io.Reader; Sscan, Sscanf and Sscanln read from an
      argument string.
  
      Scan, Fscan, Sscan treat newlines in the input as spaces.
  
      Scanln, Fscanln and Sscanln stop scanning at a newline and require that
      the items be followed by a newline or EOF.
  
      Scanf, Fscanf, and Sscanf parse the arguments according to a format
      string, analogous to that of Printf. In the text that follows, 'space'
      means any Unicode whitespace character except newline.
  
      In the format string, a verb introduced by the % character consumes and
      parses input; these verbs are described in more detail below. A
      character other than %, space, or newline in the format consumes exactly
      that input character, which must be present. A newline with zero or more
      spaces before it in the format string consumes zero or more spaces in
      the input followed by a single newline or the end of the input. A space
      following a newline in the format string consumes zero or more spaces in
      the input. Otherwise, any run of one or more spaces in the format string
      consumes as many spaces as possible in the input. Unless the run of
      spaces in the format string appears adjacent to a newline, the run must
      consume at least one space from the input or find the end of the input.
  
      The handling of spaces and newlines differs from that of C's scanf
      family: in C, newlines are treated as any other space, and it is never
      an error when a run of spaces in the format string finds no spaces to
      consume in the input.
  
      The verbs behave analogously to those of Printf. For example, %x will
      scan an integer as a hexadecimal number, and %v will scan the default
      representation format for the value. The Printf verbs %p and %T and the
      flags # and + are not implemented, and the verbs %e %E %f %F %g and %G
      are all equivalent and scan any floating-point or complex value.
  
      Input processed by verbs is implicitly space-delimited: the
      implementation of every verb except %c starts by discarding leading
      spaces from the remaining input, and the %s verb (and %v reading into a
      string) stops consuming input at the first space or newline character.
  
      The familiar base-setting prefixes 0 (octal) and 0x (hexadecimal) are
      accepted when scanning integers without a format or with the %v verb.
  
      Width is interpreted in the input text but there is no syntax for
      scanning with a precision (no %5.2f, just %5f). If width is provided, it
      applies after leading spaces are trimmed and specifies the maximum
      number of runes to read to satisfy the verb. For example,
  
          Sscanf(" 1234567 ", "%5s%d", &s, &i)
  
      will set s to "12345" and i to 67 while
  
          Sscanf(" 12 34 567 ", "%5s%d", &s, &i)
  
      will set s to "12" and i to 34.
  
      In all the scanning functions, a carriage return followed immediately by
      a newline is treated as a plain newline (\r\n means the same as \n).
  
      In all the scanning functions, if an operand implements method Scan
      (that is, it implements the Scanner interface) that method will be used
      to scan the text for that operand. Also, if the number of arguments
      scanned is less than the number of arguments provided, an error is
      returned.
  
      All arguments to be scanned must be either pointers to basic types or
      implementations of the Scanner interface.
  
      Like Scanf and Fscanf, Sscanf need not consume its entire input. There
      is no way to recover how much of the input string Sscanf used.
  
      Note: Fscan etc. can read one character (rune) past the input they
      return, which means that a loop calling a scan routine may skip some of
      the input. This is usually a problem only when there is no space between
      input values. If the reader provided to Fscan implements ReadRune, that
      method will be used to read characters. If the reader also implements
      UnreadRune, that method will be used to save the character and
      successive calls will not lose data. To attach ReadRune and UnreadRune
      methods to a reader without that capability, use bufio.NewReader.
  
  FUNCTIONS
  
  func Errorf(format string, a ...interface{}) error
      Errorf formats according to a format specifier and returns the string as
      a value that satisfies error.
  
  func Fprint(w io.Writer, a ...interface{}) (n int, err error)
      Fprint formats using the default formats for its operands and writes to
      w. Spaces are added between operands when neither is a string. It
      returns the number of bytes written and any write error encountered.
  
  func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error)
      Fprintf formats according to a format specifier and writes to w. It
      returns the number of bytes written and any write error encountered.
  
  func Fprintln(w io.Writer, a ...interface{}) (n int, err error)
      Fprintln formats using the default formats for its operands and writes
      to w. Spaces are always added between operands and a newline is
      appended. It returns the number of bytes written and any write error
      encountered.
  
  func Fscan(r io.Reader, a ...interface{}) (n int, err error)
      Fscan scans text read from r, storing successive space-separated values
      into successive arguments. Newlines count as space. It returns the
      number of items successfully scanned. If that is less than the number of
      arguments, err will report why.
  
  func Fscanf(r io.Reader, format string, a ...interface{}) (n int, err error)
      Fscanf scans text read from r, storing successive space-separated values
      into successive arguments as determined by the format. It returns the
      number of items successfully parsed. Newlines in the input must match
      newlines in the format.
  
  func Fscanln(r io.Reader, a ...interface{}) (n int, err error)
      Fscanln is similar to Fscan, but stops scanning at a newline and after
      the final item there must be a newline or EOF.
  
  func Print(a ...interface{}) (n int, err error)
      Print formats using the default formats for its operands and writes to
      standard output. Spaces are added between operands when neither is a
      string. It returns the number of bytes written and any write error
      encountered.
  
  func Printf(format string, a ...interface{}) (n int, err error)
      Printf formats according to a format specifier and writes to standard
      output. It returns the number of bytes written and any write error
      encountered.
  
  func Println(a ...interface{}) (n int, err error)
      Println formats using the default formats for its operands and writes to
      standard output. Spaces are always added between operands and a newline
      is appended. It returns the number of bytes written and any write error
      encountered.
  
  func Scan(a ...interface{}) (n int, err error)
      Scan scans text read from standard input, storing successive
      space-separated values into successive arguments. Newlines count as
      space. It returns the number of items successfully scanned. If that is
      less than the number of arguments, err will report why.
  
  func Scanf(format string, a ...interface{}) (n int, err error)
      Scanf scans text read from standard input, storing successive
      space-separated values into successive arguments as determined by the
      format. It returns the number of items successfully scanned. If that is
      less than the number of arguments, err will report why. Newlines in the
      input must match newlines in the format. The one exception: the verb %c
      always scans the next rune in the input, even if it is a space (or tab
      etc.) or newline.
  
  func Scanln(a ...interface{}) (n int, err error)
      Scanln is similar to Scan, but stops scanning at a newline and after the
      final item there must be a newline or EOF.
  
  func Sprint(a ...interface{}) string
      Sprint formats using the default formats for its operands and returns
      the resulting string. Spaces are added between operands when neither is
      a string.
  
  func Sprintf(format string, a ...interface{}) string
      Sprintf formats according to a format specifier and returns the
      resulting string.
  
  func Sprintln(a ...interface{}) string
      Sprintln formats using the default formats for its operands and returns
      the resulting string. Spaces are always added between operands and a
      newline is appended.
  
  func Sscan(str string, a ...interface{}) (n int, err error)
      Sscan scans the argument string, storing successive space-separated
      values into successive arguments. Newlines count as space. It returns
      the number of items successfully scanned. If that is less than the
      number of arguments, err will report why.
  
  func Sscanf(str string, format string, a ...interface{}) (n int, err error)
      Sscanf scans the argument string, storing successive space-separated
      values into successive arguments as determined by the format. It returns
      the number of items successfully parsed. Newlines in the input must
      match newlines in the format.
  
  func Sscanln(str string, a ...interface{}) (n int, err error)
      Sscanln is similar to Sscan, but stops scanning at a newline and after
      the final item there must be a newline or EOF.
  
  TYPES
  
  type Formatter interface {
      Format(f State, c rune)
  }
      Formatter is the interface implemented by values with a custom
      formatter. The implementation of Format may call Sprint(f) or Fprint(f)
      etc. to generate its output.
  
  type GoStringer interface {
      GoString() string
  }
      GoStringer is implemented by any value that has a GoString method, which
      defines the Go syntax for that value. The GoString method is used to
      print values passed as an operand to a %#v format.
  
  type ScanState interface {
      // ReadRune reads the next rune (Unicode code point) from the input.
      // If invoked during Scanln, Fscanln, or Sscanln, ReadRune() will
      // return EOF after returning the first '\n' or when reading beyond
      // the specified width.
      ReadRune() (r rune, size int, err error)
      // UnreadRune causes the next call to ReadRune to return the same rune.
      UnreadRune() error
      // SkipSpace skips space in the input. Newlines are treated appropriately
      // for the operation being performed; see the package documentation
      // for more information.
      SkipSpace()
      // Token skips space in the input if skipSpace is true, then returns the
      // run of Unicode code points c satisfying f(c).  If f is nil,
      // !unicode.IsSpace(c) is used; that is, the token will hold non-space
      // characters. Newlines are treated appropriately for the operation being
      // performed; see the package documentation for more information.
      // The returned slice points to shared data that may be overwritten
      // by the next call to Token, a call to a Scan function using the ScanState
      // as input, or when the calling Scan method returns.
      Token(skipSpace bool, f func(rune) bool) (token []byte, err error)
      // Width returns the value of the width option and whether it has been set.
      // The unit is Unicode code points.
      Width() (wid int, ok bool)
      // Because ReadRune is implemented by the interface, Read should never be
      // called by the scanning routines and a valid implementation of
      // ScanState may choose always to return an error from Read.
      Read(buf []byte) (n int, err error)
  }
      ScanState represents the scanner state passed to custom scanners.
      Scanners may do rune-at-a-time scanning or ask the ScanState to discover
      the next space-delimited token.
  
  type Scanner interface {
      Scan(state ScanState, verb rune) error
  }
      Scanner is implemented by any value that has a Scan method, which scans
      the input for the representation of a value and stores the result in the
      receiver, which must be a pointer to be useful. The Scan method is
      called for any argument to Scan, Scanf, or Scanln that implements it.
  
  type State interface {
      // Write is the function to call to emit formatted output to be printed.
      Write(b []byte) (n int, err error)
      // Width returns the value of the width option and whether it has been set.
      Width() (wid int, ok bool)
      // Precision returns the value of the precision option and whether it has been set.
      Precision() (prec int, ok bool)
  
      // Flag reports whether the flag c, a character, has been set.
      Flag(c int) bool
  }
      State represents the printer state passed to custom formatters. It
      provides access to the io.Writer interface plus information about the
      flags and options for the operand's format specifier.
  
  type Stringer interface {
      String() string
  }
      Stringer is implemented by any value that has a String method, which
      defines the ``native'' format for that value. The String method is used
      to print values passed as an operand to any format that accepts a string
      or to an unformatted printer such as Print.

  • 或者 godoc + 包名 + 函数名 的方式来查找某一个函数下的源码

  C:\Users\Administrator>godoc fmt Println
  use 'godoc cmd/fmt' for documentation on the fmt command
  
  func Println(a ...interface{}) (n int, err error)
      Println formats using the default formats for its operands and writes to
      standard output. Spaces are always added between operands and a newline
      is appended. It returns the number of bytes written and any write error
      encountered.

提升代码规范度

gofmt 工具可以提升代码规范度

switch 和 if 的区别

if在嵌套上比switch更有优势。

if 可以判断多个区间。

switch可以判断区间，但是只可以判断单一的区间，不可以判断多个区间。

if的执行效率比较低。

switch中的值不能是浮点型数据，浮点型数据是一个约等于的数据。

switch选择项可以是一个整形变量。