Extend spdlog for custom type

Question

Is there a way to extend spdlog to support a custom struct as an item when formatting using {}?

So when I have a

struct p {
    int x;
    int y;
    int z;
};

p my_p;

I want to do

spdlog::info("p = {}", my_p);
// after registering some kind of formatter object for {p}

instead of

spdlog::info("p = (x={}, y={}, z={})", my_p.x, my_p.y, my_p.z);

Answer 1

The accepted answer does not work anymore with newer versions of spdlog, fmt now requires specializing formatter<T> (see https://fmt.dev/latest/api.html#udt for details).

Using your p struct this is the formatter:

#include <spdlog/fmt/bundled/format.h>

template<>
struct fmt::formatter<p> {
    constexpr auto parse(format_parse_context& ctx) -> decltype(ctx.begin()) {
        return ctx.end();
    }

    template <typename FormatContext>
    auto format(const p& input, FormatContext& ctx) -> decltype(ctx.out()) {
        return format_to(ctx.out(),
            "(x={}, y={}, z={})",
            input.x, input.y, input.z);
    }
};

The parse method is used to read eventual format specifications, if you don't need them you can simply return ctx.end() and skip specifications like in the sample.