reisfmt

This is a tiny implementation, header only of the c++23 std::print for embedded systems. It only depends on some headers of the standard lib.

This implementation is heavily based on c++20 features. So you need a compiler that support the features: Concepts.

How to pull using the CMake dependency manager

<!-- CMakelist.txt -->
cmake_minimum_required(VERSION 3.13)
include(FetchContent)

FetchContent_Declare(REISFMT
  GIT_REPOSITORY    https://github.com/engdoreis/reisfmt
  GIT_TAG           <git hash>
)
FetchContent_Populate(REISFMT)

set(NAME my_app)
add_executable(${NAME} main.cc)
target_include_directories(${NAME} PRIVATE "${reisfmt_SOURCE_DIR}/include")

How to instantiate in your project

// log.hh
#include "fmt.h"
#include "uart.h"

struct LogUart{
  Uart* uart;
  // Implement your serialization here (UART, USB...)
  void write(const char* buf, size_t n) {
    while (n--) {
      uart->putc(*buf++);
    }
  }
};

using Log = reisfmt::Fmt<LogUart>;

//main.cc
#include "log.h"
//...
int main() {
// ...
  LogUart log_uart{uart0};
  Log log(log_uart);
  log.print("Hello {}", "World");
  return 0;
}

How to extend the print function for custom types

The print function can be extended to print custom types in two different ways. The first option is recommended in most cases consist in implementing the concept Printable for the desired type.

struct Memory {
  size_t addr;
  size_t size;

  // Printable concept
  template <typename T>
  inline void print(reisfmt::Fmt<T> &fmt) {
    fmt.print("Memory: addr: {:#x}, size: {}", addr, size);
  }
};

The second option is more verbose and may be needed in some cases where the type is defined by an external library. Here we specialize the struct Formatter for the desired type.

struct Memory {
  size_t addr;
  size_t size;
};

namespace reisfmt {
template <typename T>
struct Formatter<T, Memory> {
  static inline void print(Fmt<T> &fmt, Memory &obj) {
    fmt.print("Memory: addr: {:#x}, size: {}", obj.addr, obj.size);
  }
};
}

Now you can print the struct Memory using the fmt library.

  fmt_.println("{}", Memory{0x1000'0000, 1024 * 256});

Formatting specification

This library follows the c++ standard library format specification defined here.

The following features below from the specification are implemented:

Spec	Implemented
fill-and-align	yes
sign	no
#	yes
width	yes
precision	no
locale	no
type	See below

Type	Implememented
d	yes
b	yes
x	yes
o	yes
f	no
a	no
e	no
g	no
p	no
?	no