Fprint

The entire point of a file is to write things to it—to store data in it, in a persistent way. With Fprint and its family members, we can use fmt.Print() but target a file.

The names of these methods is confusing. F stands for file. And we use a method like Fprintf just like fmt.Printf—we provide a format string. A first argument (the file) must be provided.

A complete example

This program uses Fprint, Fprintf and Fprintln together. With Fprint, no newline is added at the end—this helps when not writing a file of lines.

package main

import (
    "bufio"
    "fmt"
    "os"
)

func main() {
    // Create a file and use bufio.NewWriter.
    f, _ := os.Create("C:\\programs\\file.txt")
    w := bufio.NewWriter(f)

    // Use Fprint to write things to the file.
    // ... No trailing newline is inserted.
    fmt.Fprint(w, "Hello")
    fmt.Fprint(w, 123)
    fmt.Fprint(w, "...")

    // Use Fprintf to write formatted data to the file.
    value1 := "cat"
    value2 := 900
    fmt.Fprintf(w, "%v %d...", value1, value2)

    fmt.Fprintln(w, "DONE...")

    // Done.
    w.Flush()
}
Hello123...cat 900...DONE...

Notes, file print methods

Other methods, like WriteString() on bufio can also be used to write to a file. And these may be simpler in many programs.

Writing to files is a core reason for Go's existence. Go is meant to be useful in real-world tasks. Fprint and similar methods offer a powerful tool for file writing.