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[Golang] Caveat of fmt.Fprintf Use
source link: http://siongui.github.io/2017/03/01/go-caveat-of-fmt-Fprintf-use/
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[Golang] Caveat of fmt.Fprintf Use
March 01, 2017
Do not use fmt.Fprintf to write to file.
The following code writes string to file via fmt.Fprintf:
osfmt.go | repository | view raw
package write
import (
"fmt"
"os"
)
func BadWriteStringToFile(filepath, s string) error {
fo, err := os.Create(filepath)
if err != nil {
return err
}
defer fo.Close()
_, err = fmt.Fprintf(fo, s)
if err != nil {
return err
}
return nil
}
The above code is ok if there is no % in the string. What if % in the string?
if err := BadWriteStringToFile("bad.txt", "% in string\n"); err != nil {
panic(err)
}
The output (bad.txt) is:
%!i(MISSING)n string
This is not the result we want, so what is the good way to write string to file? The answer is use io.Copy:
osiocopy.go | repository | view raw
package write
import (
"io"
"os"
"strings"
)
func WriteStringToFile(filepath, s string) error {
fo, err := os.Create(filepath)
if err != nil {
return err
}
defer fo.Close()
_, err = io.Copy(fo, strings.NewReader(s))
if err != nil {
return err
}
return nil
}
Again write the same string to file:
if err := WriteStringToFile("good.txt", "% in string\n"); err != nil {
panic(err)
}
The output (good.txt):
% in string
This is the result we want!
Tested on: Ubuntu Linux 16.10, Go 1.8.
References:
[1]os - The Go Programming Language
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