C++ library for std::format-like text formating for microcontrollers

! Warning! Library is in developing and not ready to be used in production code !

Supported features

• Presentations: b, B, c, d, o, x, X, f, F, s, p
• Flags: -, +, , 0, #, <, ^, >
• Argument position ({0}, {1}, {2:+} etc)
• Field width
• float and double types are supported (-inf, +inf and nan also works)
• Wrong type error detection

Limitations

• # not supported for float types
• L option (locale-specific formatting) not supported
• Only f presentation for float type is supported.
• Format strings like {{}.{}} not supported

How to use

Read it first. How to write "replacement fields" for output strings: https://fmt.dev/latest/syntax.html#format-specification-mini-language

Print to string buffer

char my_buffer[64];
mf::format(my_buffer, "{} {} {}", "Printing", "to", "buffer");

Callback version

1

static bool uart_format_callback(void* data, char character)
{
    uart_send_char(character);
    return true;
}

mf::format(uart_format_callback, nullptr, "{:.2} {} {:10}", 1.2f, 2, 42U);

2

template <typename ... Args>
size_t print_to_uart(const char* format, const Args& ... args)
{
    auto uart_format_callback = [](auto, char character)
    {
        uart_send_char(character);
        return true;
    };
    return mf::format(uart_format_callback, nullptr, format, args...);
}
...

print_to_uart("Hello world!!!\n");
print_to_uart("Hello {}\n", "world!!!");
print_to_uart("{} {}\n", "Hello", "world!!!");
print_to_uart("{1} {0}\n", "world!!!", "Hello");
print_to_uart("U={:8.2}v, I={:8.2}A\n", 11.2f, 0.1f);

More examples or replacement fields are in test sources: micro_format_tests.cpp

Misc functions

Library contains simple functions for non-format style convertion values to string:

• format_dec - to print integer as decimal number
• format_hex - to print integer as hexadecimal number
• format_bin - to print integer as binary number
• format_float - to print floating point number

Both "print to buffer" and callback versions are presented

mf::format_dec(my_buffer, 42);

mf::format_dec(uart_format_callback, nullptr, 42);

mf::format_float(my_buffer, 1234.5678, 4);

Using of float and double arguments

Library doesn't compile with float and double types support by default to reduce binary size of firmware. To use float type you have do define MICRO_FORMAT_FLOAT macro in you project. To use both float and double define MICRO_FORMAT_DOUBLE

Compiled binary size (gcc-arm-9 -Os)

• Binary size of compiled library without float and double support takes less than 2Kb for my cortex-m0 micrcocontroller
• Each new combination of arguments types for mf::format takes about 80 bytes
• Call mf::format for existing combination of types of arguments takes about 40 bytes