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printf-args-num-ok?
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decafe09
February 24, 2018
Programming
0
150
printf-args-num-ok?
goでprintfの引数の数をチェックするときの諸々について。
decafe09
February 24, 2018
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Transcript
printf - args num ok? Umeda.go #3 2018 - 02
- 24 @decafe09
fmt.Printf fmt.Printf("%s", "moji")
fmt.Printf fmt.Printf("%s", "moji", "yobun")
fmt.Printf $ go build # ここでは気づけない $ go run main.go
# ここで気づける moji%!(EXTRA string=yobun)
fmt.Printf $ go build # ここでは気づけない $ go run main.go
# ここで気づける moji%!(EXTRA string=yobun) func main() { http.HandleFunc( "/xxx", func(w http.ResponseWriter, r *http.Request) { fmt.Printf("%s", "moji", "yobun") return }, ) http.ListenAndServe(":8080", nil) }
fmt.Printf $ go build # ここでは気づけない $ go run main.go
# ここでは気づけない $ curl localhost:8080/xxx # ここで気づける moji%!(EXTRA string=yobun)
go vet $ go vet ./main.go:6: Printf call needs 1
arg but has 2 args go vet ! curl " go vet CI go vet
go vet –printfuncs $ go vet –printfuncs=Infof ./main.go:6: Infof call
needs 1 arg but has 2 args func Infof(format string, a ...interface{}) (n int, err error) { return fmt.Printf(format, a...) }
go vet @ Go 1.10 $ go test ./main.go:6: Printf
call needs 1 arg but has 2 args go1.9.3 main.go:6: wrong number of args for format in Printf call: 1 needed but 2 args go1.10 main.go:6: Printf call needs 1 arg but has 2 args go test go vet go test -printfuncs
Humm... format := "%s" fmt.Printf(format, "moji", ”yobun")
Humm... $ go build # ここでは気づけない $ go vet #
ここでは気づけない $ go run main.go # ここで気づける moji%!(EXTRA string=yobun) http ! % # &$"%
Background API6=3.;?>/2,BW!:20/)O APIVK" C %!8>?4+?5JSAPIRFP XXNTL@YYNTLIEH XXYYEH
XX, YY O(&'!format!O(& %D 71? +<:20/GQ&72-/M%A format#xx,yy*9=-.;?U$
Thinking... "0(' ! 0(',1#%$ /0( $ !
+.)*format !format !&-...
Result func check(format string) error 1. format %! 2. format
message 3. format %! 4. %! func main() { format := "%s" err := check(format) if err != nil { panic(err) } fmt.Println(message(format)) } func message(format string) string { return fmt.Sprintf(format, "moji", "yobun") } func check(format string) error { pre := strings.Count(format, "%!") msg := message(format) post := strings.Count(msg, "%!") if post > pre { return errors.New("format error: " + msg) } return nil }
OK All errors begin with the string "%!" followed sometimes
by a single character (the verb) and end with a parenthesized description. https://golang.org/pkg/fmt/
Check $ go run main.go panic: format error: moji%!(EXTRA string=yobun)
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