alloc::format - Rust
Description: API documentation for the Rust `format` macro in crate `alloc`.
Keywords: rust, rustlang, rust-lang, format

# Macro alloc::format 1.0.0 [−] [src]

    macro_rules! format {
        ($($arg:tt)*) => { ... };
    }

Creates a `String` using interpolation of runtime expressions.

The first argument `format!` receives is a format string. This must be a string literal. The power of the formatting string is in the `{}`s contained.

Additional parameters passed to `format!` replace the `{}`s within the formatting string in the order given unless named or positional parameters are used, see `std::fmt` for more information.

A common use for `format!` is concatenation and interpolation of strings. The same convention is used with `print!` and `write!` macros, depending on the intended destination of the string.

# Panics

`format!` panics if a formatting trait implementation returns an error. This indicates an incorrect implementation since `fmt::Write for String` never returns an error itself.

# Examples

    format!("test");
    format!("hello {}", "world!");
    format!("x = {}, y = {y}", 10, y = 30);

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