# Macro std::format_args 1.0.0[−][src]

    macro_rules! format_args {
        ($fmt:expr) => { ... };
        ($fmt:expr, $($args:tt)*) => { ... };
    }

The core macro for formatted string creation & output.

This macro functions by taking a formatting string literal containing `{}` for each additional argument passed. `format_args!` prepares the additional parameters to ensure the output can be interpreted as a string and canonicalizes the arguments into a single type. Any value that implements the `Display` trait can be passed to `format_args!`, as can any `Debug` implementation be passed to a `{:?}` within the formatting string.

This macro produces a value of type `fmt::Arguments`. This value can be passed to the macros within `std::fmt` for performing useful redirection. All other formatting macros (`format!`, `write!`, `println!`, etc) are proxied through this one. `format_args!`, unlike its derived macros, avoids heap allocations.

You can use the `fmt::Arguments` value that `format_args!` returns in `Debug` and `Display` contexts as seen below. The example also shows that `Debug` and `Display` format to the same thing: the interpolated format string in `format_args!`.

    let debug = format!("{:?}", format_args!("{} foo {:?}", 1, 2));
    let display = format!("{}", format_args!("{} foo {:?}", 1, 2));
    assert_eq!("1 foo 2", display);
    assert_eq!(display, debug);Run

For more information, see the documentation in `std::fmt`.

# Examples

    use std::fmt;

    let s = fmt::format(format_args!("hello {}", "world"));
    assert_eq!(s, format!("hello {}", "world"));Run

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)

Search multiple things at once by splitting your query with comma (e.g. `str,u8` or `String,struct:Vec,test`)