@fmt

The @fmt module provides printf-style formatted output, string padding, and number formatting.

Import

import @fmt

Formatted Output

printf()

(format string, ...args T)

Prints a formatted string to stdout.

import @fmt

do main() {
    fmt.printf("Hello, %s! You are %d years old.\n", "Alice", 30)
    fmt.printf("Pi is approximately %.4f\n", 3.14159)
}

printfln()

(format string, ...args T)

Prints a formatted string to stdout with a trailing newline.

fmt.printfln("Hello, %s!", "Alice")  // prints "Hello, Alice!\n"

eprintf()

(format string, ...args T)

Prints a formatted string to stderr (no trailing newline).

fmt.eprintf("Error: %s", "connection failed")

eprintfln()

(format string, ...args T)

Prints a formatted string to stderr with a trailing newline.

fmt.eprintfln("Error: %s (code %d)", "timeout", 408)

sprintf()

(format string, ...args T) -> string

Returns a formatted string (does not print).

import @fmt

do main() {
    mut msg = fmt.sprintf("Score: %d/%d", 85, 100)
    println(msg)  // "Score: 85/100"
}

sprintfln()

(format string, ...args T) -> string

Returns a formatted string with a trailing newline (does not print).

mut line string = fmt.sprintfln("Score: %d/%d", 85, 100)
// line is "Score: 85/100\n"

format()

(format string, ...args T) -> string

Alias for sprintf(). Returns a formatted string.

Padding

pad_left()

(s string, width int, ch char) -> string

Pads a string on the left to the given width with the specified character.

import @fmt

do main() {
    println(fmt.pad_left("42", 5, '0'))    // "00042"
    println(fmt.pad_left("hi", 10, ' '))   // "        hi"
}

pad_right()

(s string, width int, ch char) -> string

Pads a string on the right to the given width with the specified character.

import @fmt

do main() {
    println(fmt.pad_right("Name", 10, '.'))  // "Name......"
}

center()

(s string, width int, ch char) -> string

Centers a string within the given width, padding both sides with the specified character.

import @fmt

do main() {
    println(fmt.center("title", 20, '='))  // "=======title========"
}

Number Formatting

int_to_hex()

(n int) -> string

Formats an integer as lowercase hexadecimal (no 0x prefix).

println(fmt.int_to_hex(255))   // "ff"
println(fmt.int_to_hex(4096))  // "1000"

int_to_binary()

(n int) -> string

Formats an integer as binary.

println(fmt.int_to_binary(10))   // "1010"
println(fmt.int_to_binary(255))  // "11111111"

int_to_octal()

(n int) -> string

Formats an integer as octal.

println(fmt.int_to_octal(8))    // "10"
println(fmt.int_to_octal(255))  // "377"

float_fixed()

(f float, decimals int) -> string

Formats a float with a fixed number of decimal places.

println(fmt.float_fixed(3.14159, 2))  // "3.14"
println(fmt.float_fixed(1.0, 4))      // "1.0000"

float_sci()

(f float) -> string

Formats a float in scientific notation.

println(fmt.float_sci(123456.789))  // "1.234568e+05"
println(fmt.float_sci(0.00042))     // "4.200000e-04"

Notes

printf, sprintf, and format accept string, int, float, and bool arguments. Composite types (structs, arrays, maps) are not supported — use println for printing those.