ostreams

A constexpr output stream implementation. See tests for example of usage

To create a formatted buffer

daw::static_string_t<char, 100> buffer{};   // Uses a static string, but any contiguous memory area is fine

buffer.resize(buffer.size( ));  // makes static string marked as fully used


auto buff_stream = daw::io::make_memory_buffer_stream( buffer.data( ), buffer.size( ) );    // create stream

buff_stream << "The meaning of life is " << 42 << '\n';

buffer.shrink_to_fit( );    // reclaim unused space in buffer

Console output

daw::con_out << "The meaning of life is " << 42 << '\n';

File output

auto fs = daw::make_file_stream( "file_name" );
if( !fs ) {
    daw::con_err << "Error opening file\n";
    exit( EXIT_FAILURE );
}
fs << "The meaining of life is " << 42 << '\n';
fs.close( );    // or let it go out of scope

Extending to your classes

Add a function to_os_string<CharT>( ClassType ) in your classes namespace that returns a type that is string like(has data( ) and size( )methods). If you want constexpr formatting this function must be constexpr. The provided static_string_t<CharT> can help or a string_view may work too.

Custom streams must provide operator() for character and string like data. They must also specialize daw::io::supports_output_stream_interface<T> to inherit from std::true_type

Otherwise, for composite classes you would overload operator<< like in C++ iostreams. The requirement being that it is a template and uses SFINAE to only allow when daw::io::is_output_stream_v<OutputStream> == true.

Benchmarks

Using a format string(or equivilent) of "The asnwer to the meaning of life is %d %f\n" with a double of 42.0

The following are the results:

Mac 2017 Macbook Air - 1.8 GHz Intel Core i5

method	count	total time	item time
daw::memory_stream	100000	13.90ms	138.99ns
snprintf	100000	31.98ms	319.83ns
std::string_stream	100000	77.30ms	772.96ns
printf	100000	170.57ms	1.71us
daw::con_err	100000	573.81ms	5.74us
std::cerr	100000	800.21ms	8.00us

Windows Intel i7-7500U

method	count	total time	item time
daw::memory_stream	100000	21.70ms	217.00ns
snprintf	100000	96.02ms	960.96ns
std::string_stream	100000	127.61ms	1.28us
daw::con_err	100000	326.27ms	3.26us
std::cerr	100000	842.78ms	8.43us
printf	100000	3.99s	39.86us

Round trip errors

Tested using strtod/strtof to return string to a double/float

type	value	output	difference
double	0.1	0.1	0
double	0.12	0.11999999999999998	-1.38778e-17
double	0.123	0.12299999999999999	-1.38778e-17
double	0.1234	0.12339999999999998	-1.38778e-17
double	1.2345	1.23449999999999992	0
double	0.333333	0.33333333333333332	0
double	0.666667	0.66666666666666665	0
double	3.33333	3.33333333333333349	0
double	6.66667	6.66666666666666698	0
double	2.22507e-308	0.0000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 0000000022250738585072009	-4.94066e-324
double	-2.22507e-308	-0.00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 000000022250738585072009	4.94066e-324
double	1.79769e+308	17976931348623156600000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 000000000	0
double	4.94066e-324	0	-4.94066e-324
double	4	3.99999999999999953	0
double	8.98847e+307	89884656743115786500000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000000000000000000000000000000000000000000000 00000000	0
float	0.1	0.1	0
float	0.12	0.119999996	0
float	0.123	0.123000001	0
float	0.1234	0.123400000	0
float	1.2345	1.234500046	0
float	0.333333	0.333333330	0
float	0.666667	0.666666660	0
float	3.33333	3.333333240	0
float	6.66667	6.666666481	0
float	1.17549e-38	0.0000000000000000000000000000000000000117549440	0
float	3.40282e+38	340282346300000000000000000000000000000	0
float	1.4013e-45	0	-1.4013e-45
float	4	3.999999788	0
float	1.70141e+38	170141175700000000000000000000000000000	0