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std.fmt

Formatting utilities for converting values to strings.

Functions

format_i32

def format_i32(buf: ptr[char], value: int32) -> uint64

Format a signed 32-bit integer as a decimal string into buf. Writes a null terminator. Returns the number of characters written (excluding the null terminator).

from std.fmt import format_i32
from std.alloc import alloc
from std.io import puts

pub def main() -> int32:
    let buf: ptr[char] = alloc(16)
    let len = format_i32(buf, -42)
    # buf == "-42\0", len == 3
    puts(buf)
    free(buf)
    return 0

format_f64

def format_f64(buf: ptr[char], value: float64) -> uint64

Format a 64-bit float as a decimal string into buf. Writes a null terminator. Returns the number of characters written. x86_64 only.

let len = format_f64(buf, 3.14)

Buffer Requirements

• The buffer must be large enough for the result plus the null terminator
• Maximum for int32: 12 bytes (“-2147483648” + null)
• Allocate generously (16 bytes is a safe default)

Implementation Notes

• Pure software implementation (no syscalls)
• Division-based algorithm, not optimized for speed
• No locale support (always decimal, no thousands separator)
• No padding or alignment options

Planned Extensions

format_u32, format_i64, format_u64, format_ptr, and sprintf-style formatting are future work.

Target Support

All targets: pure software, no syscalls needed (format_f64 is x86_64 only).

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