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Color and text styles

Terminal color is a formatting concern, and fmt handles it with the same type-safe API used everywhere else instead of leaving you to paste raw ANSI escape codes into string literals.

Basic use​

#include <fmt/color.h>

fmt::print(fg(fmt::color::crimson) | fmt::emphasis::bold, "{}\n", msg);

fg(color) sets the foreground color; combined with fmt::emphasis::bold via |, the whole thing is a fmt::text_style object that any fmt::print/fmt::format call accepts as its first argument.

The pieces​

fg(color) sets foreground, bg(color) sets background, and fmt::emphasis covers bold, italic, underline, and strikethrough — all combinable with |.

APIPalettePortability
fmt::terminal_color8/16-color ANSI paletteWorks on nearly every terminal, including old ones
fmt::color24-bit RGBNeeds a truecolor-capable terminal

Prefer fmt::terminal_color for output that has to work in a plain SSH session or CI log; reach for fmt::color's full RGB range when you know the target terminal supports it.

fmt::styled​

fmt::styled(value, style) attaches a style to a single argument inside a larger format string, rather than styling the whole call.

fmt::print("Status: {}\n", fmt::styled("OK", fg(fmt::color::green) | fmt::emphasis::bold));

Getting it into a string​

fmt::format(fg(...), ...) embeds the ANSI escape codes directly in the returned string — useful when the result is going to a terminal-writing function that doesn't take a style argument itself.

Redirection​

fmt does not detect whether the output is a TTY — escape codes will land in your log file if you redirect

fmt::print(fg(fmt::color::red), "error\n") writes raw ANSI escapes into whatever stdout currently points at. Redirected to a file or piped into a log aggregator that doesn't strip ANSI, those escape codes show up as garbage characters. Check isatty (or your platform's equivalent) yourself and pick a style-free formatting path when the destination isn't a terminal.

Windows​

On older Windows consoles the escapes print literally unless VT mode is enabled

Windows consoles didn't historically interpret ANSI escape sequences at all; virtual terminal (VT) processing has to be enabled explicitly (ENABLE_VIRTUAL_TERMINAL_PROCESSING via SetConsoleMode) before colored fmt output renders correctly instead of printing the raw escape bytes.

See also​