Printf · The Julia Language
Description: Documentation for The Julia Language.

# Printf

The `Printf` module provides formatted output functions similar to the C standard library's `printf`. It allows formatted printing to an output stream or to a string.

`Printf.@printf` — Macro

    @printf([io::IO], "%Fmt", args...)

Print `args` using C `printf` style format specification string. Optionally, an `IO` may be passed as the first argument to redirect output.

Examples

    julia> @printf "Hello %s" "world"
    Hello world

    julia> @printf "Scientific notation %e" 1.234
    Scientific notation 1.234000e+00

    julia> @printf "Scientific notation three digits %.3e" 1.23456
    Scientific notation three digits 1.235e+00

    julia> @printf "Decimal two digits %.2f" 1.23456
    Decimal two digits 1.23

    julia> @printf "Padded to length 5 %5i" 123
    Padded to length 5   123

    julia> @printf "Padded with zeros to length 6 %06i" 123
    Padded with zeros to length 6 000123

    julia> @printf "Use shorter of decimal or scientific %g %g" 1.23 12300000.0
    Use shorter of decimal or scientific 1.23 1.23e+07

    julia> @printf "Use dynamic width and precision  %*.*f" 10 2 0.12345
    Use dynamic width and precision        0.12

For a systematic specification of the format, see here. See also `@sprintf` to get the result as a `String` instead of it being printed.

Caveats

`Inf` and `NaN` are printed consistently as `Inf` and `NaN` for flags `%a`, `%A`, `%e`, `%E`, `%f`, `%F`, `%g`, and `%G`. Furthermore, if a floating point number is equally close to the numeric values of two possible output strings, the output string further away from zero is chosen.

Examples

    julia> @printf("%f %F %f %F", Inf, Inf, NaN, NaN)
    Inf Inf NaN NaN

    julia> @printf "%.0f %.1f %f" 0.5 0.025 -0.0078125
    0 0.0 -0.007812

Julia 1.8

Starting in Julia 1.8, `%s` (string) and `%c` (character) widths are computed using `textwidth`, which e.g. ignores zero-width characters (such as combining characters for diacritical marks) and treats certain "wide" characters (e.g. emoji) as width `2`.

Julia 1.10

Dynamic width specifiers like `%*s` and `%0*.*f` require Julia 1.10.

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`Printf.@sprintf` — Macro

    @sprintf("%Fmt", args...)

Return `@printf` formatted output as string.

Examples

    julia> @sprintf "this is a %s %15.1f" "test" 34.567
    "this is a test            34.6"

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`Printf.Format` — Type

    Printf.Format(format_str)

Create a C printf-compatible format object that can be used for formatting values.

The input `format_str` can include any valid format specifier character and modifiers.

A `Format` object can be passed to `Printf.format(f::Format, args...)` to produce a formatted string, or `Printf.format(io::IO, f::Format, args...)` to print the formatted string directly to `io`.

For convenience, the `Printf.format"..."` string macro form can be used for building a `Printf.Format` object at macro-expansion-time.

Julia 1.6

`Printf.Format` requires Julia 1.6 or later.

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`Printf.format` — Function

    Printf.format(f::Printf.Format, args...) => String
    Printf.format(io::IO, f::Printf.Format, args...)

Apply a printf format object `f` to provided `args` and return the formatted string (1st method), or print directly to an `io` object (2nd method). See `@printf` for more details on C `printf` support.

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This document was generated with Documenter.jl version 1.17.0 on Thursday 9 April 2026. Using Julia version 1.12.6.