# package log
`import "log"`
log包实现了简单的日志服务。本包定义了Logger类型，该类型提供了一些格式化输出的方法。本包也提供了一个预定义的“标准”Logger，可以通过辅助函数Print[f|ln]、Fatal[f|ln]和Panic[f|ln]访问，比手工创建一个Logger对象更容易使用。Logger会打印每条日志信息的日期、时间，默认输出到标准错误。Fatal系列函数会在写入日志信息后调用os.Exit(1)。Panic系列函数会在写入日志信息后panic。
## Index
* [Constants](#pkg-constants)
* [type Logger](#Logger)
* [func New(out io.Writer, prefix string, flag int) \*Logger](#New)
* [func (l \*Logger) Flags() int](#Logger.Flags)
* [func (l \*Logger) SetFlags(flag int)](#Logger.SetFlags)
* [func (l \*Logger) Prefix() string](#Logger.Prefix)
* [func (l \*Logger) SetPrefix(prefix string)](#Logger.SetPrefix)
* [func (l \*Logger) Output(calldepth int, s string) error](#Logger.Output)
* [func (l \*Logger) Printf(format string, v ...interface{})](#Logger.Printf)
* [func (l \*Logger) Print(v ...interface{})](#Logger.Print)
* [func (l \*Logger) Println(v ...interface{})](#Logger.Println)
* [func (l \*Logger) Fatalf(format string, v ...interface{})](#Logger.Fatalf)
* [func (l \*Logger) Fatal(v ...interface{})](#Logger.Fatal)
* [func (l \*Logger) Fatalln(v ...interface{})](#Logger.Fatalln)
* [func (l \*Logger) Panic(v ...interface{})](#Logger.Panic)
* [func (l \*Logger) Panicf(format string, v ...interface{})](#Logger.Panicf)
* [func (l \*Logger) Panicln(v ...interface{})](#Logger.Panicln)
* [func Flags() int](#Flags)
* [func SetFlags(flag int)](#SetFlags)
* [func Prefix() string](#Prefix)
* [func SetPrefix(prefix string)](#SetPrefix)
* [func SetOutput(w io.Writer)](#SetOutput)
* [func Printf(format string, v ...interface{})](#Printf)
* [func Print(v ...interface{})](#Print)
* [func Println(v ...interface{})](#Println)
* [func Fatalf(format string, v ...interface{})](#Fatalf)
* [func Fatal(v ...interface{})](#Fatal)
* [func Fatalln(v ...interface{})](#Fatalln)
* [func Panicf(format string, v ...interface{})](#Panicf)
* [func Panic(v ...interface{})](#Panic)
* [func Panicln(v ...interface{})](#Panicln)
### Examples
* [Logger](#example-Logger)
## Constants
```
const (
// 字位共同控制输出日志信息的细节。不能控制输出的顺序和格式。
// 在所有项目后会有一个冒号：2009/01/23 01:23:23.123123 /a/b/c/d.go:23: message
Ldate = 1 << iota // 日期：2009/01/23
Ltime // 时间：01:23:23
Lmicroseconds // 微秒分辨率：01:23:23.123123（用于增强Ltime位）
Llongfile // 文件全路径名+行号： /a/b/c/d.go:23
Lshortfile // 文件无路径名+行号：d.go:23（会覆盖掉Llongfile）
LstdFlags = Ldate | Ltime // 标准logger的初始值
)
```
这些选项定义Logger类型如何生成用于每条日志的前缀文本。
## type [Logger](https://github.com/golang/go/blob/master/src/log/log.go#L42 "View Source")
```
type Logger struct {
// contains filtered or unexported fields
}
```
Logger类型表示一个活动状态的记录日志的对象，它会生成一行行的输出写入一个io.Writer接口。每一条日志操作会调用一次io.Writer接口的Write方法。Logger类型的对象可以被多个线程安全的同时使用，它会保证对io.Writer接口的顺序访问。
Example
```
var buf bytes.Buffer
logger := log.New(&buf, "logger: ", log.Lshortfile)
logger.Print("Hello, log file!")
fmt.Print(&buf)
```
Output:
```
logger: example_test.go:16: Hello, log file!
```
### func [New](https://github.com/golang/go/blob/master/src/log/log.go#L54 "View Source")
```
func New(out io.Writer, prefix string, flag int) *Logger
```
New创建一个Logger。参数out设置日志信息写入的目的地。参数prefix会添加到生成的每一条日志前面。参数flag定义日志的属性（时间、文件等等）。
### func (\*Logger) [Flags](https://github.com/golang/go/blob/master/src/log/log.go#L211 "View Source")
```
func (l *Logger) Flags() int
```
Flags返回logger的输出选项。
### func (\*Logger) [SetFlags](https://github.com/golang/go/blob/master/src/log/log.go#L218 "View Source")
```
func (l *Logger) SetFlags(flag int)
```
SetFlags设置logger的输出选项。
### func (\*Logger) [Prefix](https://github.com/golang/go/blob/master/src/log/log.go#L225 "View Source")
```
func (l *Logger) Prefix() string
```
Prefix返回logger的输出前缀。
### func (\*Logger) [SetPrefix](https://github.com/golang/go/blob/master/src/log/log.go#L232 "View Source")
```
func (l *Logger) SetPrefix(prefix string)
```
SSetPrefix设置logger的输出前缀。
### func (\*Logger) [Output](https://github.com/golang/go/blob/master/src/log/log.go#L130 "View Source")
```
func (l *Logger) Output(calldepth int, s string) error
```
Output写入输出一次日志事件。参数s包含在Logger根据选项生成的前缀之后要打印的文本。如果s末尾没有换行会添加换行符。calldepth用于恢复PC，出于一般性而提供，但目前在所有预定义的路径上它的值都为2。
### func (\*Logger) [Printf](https://github.com/golang/go/blob/master/src/log/log.go#L159 "View Source")
```
func (l *Logger) Printf(format string, v ...interface{})
```
Printf调用l.Output将生成的格式化字符串输出到logger，参数用和fmt.Printf相同的方法处理。
### func (\*Logger) [Print](https://github.com/golang/go/blob/master/src/log/log.go#L165 "View Source")
```
func (l *Logger) Print(v ...interface{})
```
Print调用l.Output将生成的格式化字符串输出到logger，参数用和fmt.Print相同的方法处理。
### func (\*Logger) [Println](https://github.com/golang/go/blob/master/src/log/log.go#L169 "View Source")
```
func (l *Logger) Println(v ...interface{})
```
Println调用l.Output将生成的格式化字符串输出到logger，参数用和fmt.Println相同的方法处理。
### func (\*Logger) [Fatalf](https://github.com/golang/go/blob/master/src/log/log.go#L178 "View Source")
```
func (l *Logger) Fatalf(format string, v ...interface{})
```
Fatalf等价于{l.Printf(v...); os.Exit(1)}
### func (\*Logger) [Fatal](https://github.com/golang/go/blob/master/src/log/log.go#L172 "View Source")
```
func (l *Logger) Fatal(v ...interface{})
```
Fatal等价于{l.Print(v...); os.Exit(1)}
### func (\*Logger) [Fatalln](https://github.com/golang/go/blob/master/src/log/log.go#L184 "View Source")
```
func (l *Logger) Fatalln(v ...interface{})
```
Fatalln等价于{l.Println(v...); os.Exit(1)}
### func (\*Logger) [Panicf](https://github.com/golang/go/blob/master/src/log/log.go#L197 "View Source")
```
func (l *Logger) Panicf(format string, v ...interface{})
```
Panicf等价于{l.Printf(v...); panic(...)}
### func (\*Logger) [Panic](https://github.com/golang/go/blob/master/src/log/log.go#L190 "View Source")
```
func (l *Logger) Panic(v ...interface{})
```
Panic等价于{l.Print(v...); panic(...)}
### func (\*Logger) [Panicln](https://github.com/golang/go/blob/master/src/log/log.go#L204 "View Source")
```
func (l *Logger) Panicln(v ...interface{})
```
Panicln等价于{l.Println(v...); panic(...)}
## func [Flags](https://github.com/golang/go/blob/master/src/log/log.go#L246 "View Source")
```
func Flags() int
```
Flags返回标准logger的输出选项。
## func [SetFlags](https://github.com/golang/go/blob/master/src/log/log.go#L251 "View Source")
```
func SetFlags(flag int)
```
SetFlags设置标准logger的输出选项。
## func [Prefix](https://github.com/golang/go/blob/master/src/log/log.go#L256 "View Source")
```
func Prefix() string
```
Prefix返回标准logger的输出前缀。
## func [SetPrefix](https://github.com/golang/go/blob/master/src/log/log.go#L261 "View Source")
```
func SetPrefix(prefix string)
```
SetPrefix设置标准logger的输出前缀。
## func [SetOutput](https://github.com/golang/go/blob/master/src/log/log.go#L239 "View Source")
```
func SetOutput(w io.Writer)
```
SetOutput设置标准logger的输出目的地，默认是标准错误输出。
## func [Printf](https://github.com/golang/go/blob/master/src/log/log.go#L275 "View Source")
```
func Printf(format string, v ...interface{})
```
Printf调用Output将生成的格式化字符串输出到标准logger，参数用和fmt.Printf相同的方法处理。
## func [Print](https://github.com/golang/go/blob/master/src/log/log.go#L269 "View Source")
```
func Print(v ...interface{})
```
Print调用Output将生成的格式化字符串输出到标准logger，参数用和fmt.Print相同的方法处理。
## func [Println](https://github.com/golang/go/blob/master/src/log/log.go#L281 "View Source")
```
func Println(v ...interface{})
```
Println调用Output将生成的格式化字符串输出到标准logger，参数用和fmt.Println相同的方法处理。
## func [Fatalf](https://github.com/golang/go/blob/master/src/log/log.go#L292 "View Source")
```
func Fatalf(format string, v ...interface{})
```
Fatalf等价于{Printf(v...); os.Exit(1)}
## func [Fatal](https://github.com/golang/go/blob/master/src/log/log.go#L286 "View Source")
```
func Fatal(v ...interface{})
```
Fatal等价于{Print(v...); os.Exit(1)}
## func [Fatalln](https://github.com/golang/go/blob/master/src/log/log.go#L298 "View Source")
```
func Fatalln(v ...interface{})
```
Fatalln等价于{Println(v...); os.Exit(1)}
## func [Panicf](https://github.com/golang/go/blob/master/src/log/log.go#L311 "View Source")
```
func Panicf(format string, v ...interface{})
```
Panicf等价于{Printf(v...); panic(...)}
## func [Panic](https://github.com/golang/go/blob/master/src/log/log.go#L304 "View Source")
```
func Panic(v ...interface{})
```
Panic等价于{Print(v...); panic(...)}
## func [Panicln](https://github.com/golang/go/blob/master/src/log/log.go#L318 "View Source")
```
func Panicln(v ...interface{})
```
Panicln等价于{Println(v...); panic(...)}
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