constexpr number <-> string composition, formatting and conversions with full support of unterminated string views. I started my journey with C++ in the 2004 with compilers like embedded visual c++ 4, gcc 2.95. Thru years of participation in big projects i have had to fix many errors that source was in string formatting like vnprintf.
The source of problems I have many time found was:
- there was no consistency between formatting string and arguments, that was source of errors detected at runtime.
- string composition was always done at runtime even if some operations and arguments were known and could be used at compile time
- all that C library functions require null terminated C strings
- formatting information for example in vsnprintf could not be easily shared/reused across project.
- working on pointers to null terminated strings often causes a lot of redundant strlen and dangling pointer errors
This code solves those problems:
- formatting information is attached to arguments and prevents mismatching formatting with argument type errors at compile time
- every conversion, composing, formatting is constexpr except allocations
- full support for std::string_view with not null terminated strings
- formatting traits can be declared constexpr constant and reused consistently across project
- minimum c++20 compiler required (stl at least c++17)
- fully constexpr string to number and number to string conversion for functions that doesn't allocate (using output iterators)
- extensive number formating with constexpr traits
- merging string_views and composing any data (string_views, numbers) with one variadic template, one allocation
- compose, merge doesn't allow using directly pointers to chars and char tables (usable only with std::basic_string_view), to disallow working with pointers
- supports std::basic_string and my own coll::basic_string
- stralgo::utf - fully constant evaluated utf8,16,32 string manipulation with formatters for char format
- header only, except unit tests
At this point of early development I work with clang 15,16,17 and gcc-12,gcc-13. I'm planing checking and porting to msvc in near future.
- this header only library integrates with cpm my other repository small_vectors and uses from it fully constexpr coll::basic_string and coll::basic_fixed_string for unit tests
{
//main feature compose with constexpr formatting except final allocation
using stralgo::integral_format_traits;
using stralgo::format_e;
using stralgo::char_case_e;
using stralgo::prepend_sign_e;
using stralgo::padd_with_e;
using stralgo::include_prefix_e;
using stralgo::alignment_e;
constexpr integral_format_traits ptrfmt //reusable formatting traits
{
.precision = 6, //minimum precision/size of output text
.format = format_e::hexadecimal,
.char_case = char_case_e::uppercase,
.padd_with = padd_with_e::zeros //fill space with zeros
};
//output string value type is deduced as char
auto strres {
//stralgo::compose uses my own coll::basic_string_view
stralgo::stl::compose(
" some view "sv,
127.3f, //default formatted floating point see float_format_traits{}
',', ///single char
125, //default formatted integral number see integral_format_traits{}
'[',
stralgo::fmt<integral_format_traits{
.precision = 15, //minimum number of characters
.format = format_e::binary, //output format encoding of digit numbers
.char_case = char_case_e::lowercase, //char case when using hexadecimal format
.padd_with = padd_with_e::space, //pad value with zeros or space when precision is higher than value representation
.sign = prepend_sign_e::only_negative, //prepend sign to result string
.include_prefix = include_prefix_e::with_prefix, //include prefix when defined for format ex: for hexadecimal 0x
.alignment = alignment_e::middle //alignment when padding with space
}>(456), //custom formatted integral number with traits like in integral_to_string
"] ["sv,
stralgo::fmt<stralgo::float_format_traits{
.precision = 10,
.decimal_places = 2,
.alignment = stralgo::alignment_e::left,
.trailing_zeros = stralgo::trailing_zeros_e::skip
}>(10.46713), //custom formatted floating point number with traits like in float_to_string
"] "sv,
fmt<ptrfmt>(0x1ff56ef001), ' ', //reuse custom constexpr formatting
fmt<ptrfmt>(0x0)
) };
constexpr auto expected{ " some view 127.300003,125[ 0b111001000 ] [10.46 ] 0X1FF56EF001 0X0000"sv };
}
```
### stralgo::merge
merge does same as compose except that it i simpler form limited to views and chars
```C++
string_view t1a {"orem ipsum dolor sit amet, consectetur adipiscing elit. "sv}, t2a { }, t3a {"Vestibulum"sv }; char t4a{' '}; string_view t5a{"rutrum leo libero"};
//stralgo::merge uses my own coll::basic_string_view
auto resa{ stralgo::stl::merge('L',t1a,t2a,t3a,t4a,t5a)};
constexpr string_view expected{"Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum rutrum leo libero"};
Converting and formatting integral numbers. Building block of compose that can be use separately
There are 2 variants available
- one returning string
- second constexpr storing result at output iterator returning iterator pass the end last stored char
//non constexpr returning string
using traits = stralgo::integral_format_traits;
{
constexpr int64_t value{ -0x1ffeb3ef1ffeb3ll };
constexpr auto expected{ " -0x1ffeb3ef1ffeb3 "sv };
auto result = stralgo::integral_to_string<traits{ .precision = 22,
.format = format_e::hexadecimal,
.char_case = char_case_e::lowercase,
.sign = prepend_sign_e::only_negative,
.alignment = alignment_e::middle
}>( value );
static_assert( expected == result );
}
//example constexpr use without buffer allocation
constexpr bool test_unsigned_9d()
{
char buffer_[integral_to_string_max_size]{};
auto itbeg{ &buffer_[0] };
constexpr int64_t value{ -0b1100110011001100110011001100110011001100110011001100110011001ll };
constexpr std::string_view expected{ " -1100110011001100110011001100110011001100110011001100110011001" };
auto oit = stralgo::integral_to_string<traits{.precision = 68,
.format = format_e::binary,
.padd_with = padd_with_e::space,
.include_prefix = include_prefix_e::no_prefix
}>( value, itbeg );
std::string_view result{ itbeg, static_cast<std::string_view::size_type>(oit-itbeg) };
return expected == result;
}
static_assert( test_unsigned_9d() );
```
### stralgo::string_to_integral
Converting string representation of integral numbers.
Returns converted number value and iterator pass the end of source string view where conversion stopped
Example as constexpr test function
```C++
using stralgo::string_to_integral;
using namespace std::string_view_literals;
using stralgo::input_format_e;
template<typename integral_type,
input_format_e input_format = input_format_e::undetermined,
typename expected_type>
constexpr auto test( std::string_view source, expected_type expected, int end_it_offset )
{
auto [result,end_it] = string_to_integral<integral_type,input_format>(source);
return std::next(std::begin(source),end_it_offset) == end_it
&& static_cast<integral_type>(expected) == result;
}
//format determined at function based on prefix
static_assert( test<uint16_t>("255"sv,255u,3) );
static_assert( test<uint8_t>(" \t0xff 0xfe"sv,255u,6) );
static_assert( test<int64_t>("\t \t -0x1aF3423R342fsdv"sv,-0x1af3423,14) );
//format explicitly specified, prefix is not required
static_assert( test<uint8_t,input_format_e::hexadecimal>(" \t0xff 0xfe"sv,255u,6) );
static_assert( test<uint8_t,input_format_e::hexadecimal>(" \tff 0xfe"sv,255u,4) );
```
### stralgo::string_to_float
Converting string representation of float numbers.
```C++
using stralgo::string_to_float;
using namespace std::string_view_literals;
template<typename float_type, typename expected_type>
constexpr auto test( std::string_view source, expected_type expected, int end_it_offset )
{
auto [result,end_it] = string_to_float<float_type>(source);
return std::next(std::begin(source),end_it_offset) == end_it
&& static_cast<float_type>(expected) == result;
}
static_assert( test<double>("10.1333"sv, 10.1333, 7 ) );
static_assert( test<double>("+10.1333"sv, 10.1333, 8 ) );
static_assert( test<double>("-10.1333"sv, -10.1333, 8 ) );
```
### stralgo::float_to_string
Converts floating point number into string representation
There are 2 variants available
* one returning string
* second constexpr storing result at output iterator returning iterator pass the end last stored char
Example using output iterator
```C++
constexpr bool test_float_4a()
{
char buffer_[integral_to_string_max_size]{};
auto itbeg{ &buffer_[0] };
constexpr double value{ 0.5 };
constexpr std::string_view expected{ "00000.5000" };
auto oit = stralgo::float_to_string<traits{
.precision = 10,
.decimal_places = 4,
.padd_with = padd_with_e::zeros,
.trailing_zeros = trailing_zeros_e::preserve
}>( value, itbeg );
std::string_view result{ itbeg, static_cast<std::string_view::size_type>(oit-itbeg) };
return expected == result;
}
static_assert( test_float_4a() );- utf_input_view_t - utf view over range
- deducing utf_forward_iterator_t
- deducing utf_output_iterator_t with typed output iterators
- utf_explicit_output_iterator_t for use with untyped outpt iterators (new in version 1.3.0)
- formatters of utf char16_t,char32_t,wchar_t for std::format char
- length - number of code points in range
- capacity_t<char_type> - number of bytes required to encode range into given char type, ie char8_t, char16_t, char32_t, wchar_t ...
- convert - convert range into output iterator with other utf encoding
- to_string_t<char_type> - convert utf range into coll::basic_string<> or std::basic_string<> with other utf encoding
- verify - verification of utf range
namespace utf = stralgo::utf;
// any range (string string_view, array, vector ...) to output iterator with tpe deduction
constexpr auto view( auto const & a ) noexcept
{ return std::basic_string_view{ std::begin(a), std::end(a)}; }
constexpr std::basic_string_view u8test{u8"πππππππππππππππ"};
constexpr std::basic_string_view u16test{u16"πππππππππππππππ"};
std::array<char16_t, u16test.size()> storage;
utf::convert( u8test, std::begin(storage));
constexpr_test( view(storage) == u16test );
//any range to own string
constexpr_test( utf::to_u16string(u8test) == u16test );
//any range to std string
std::u16string str2 = utf::stl::to_u16string(u8test);
constexpr_test( str2 == u16test );Performance comparison of compose vs snprintf for bellow test functions
Ryzen 9 - 5900X
| compiler | function | stralgo | legacy |
|---|---|---|---|
| clang-16 | compose | 17 ms | 42 ms |
| gcc-12 | compose | 23 ms | 42 ms |
full implementation performance comparison can be seen in perf/perf.cc
//example compose test
stralgo::compose<char>( 'T',
data.example_string, ' ',
data.emaple_float,
' ',
stralgo::fmt<stralgo::integral_format_traits{
.precision = 11,
.format = format_e::hexadecimal,
.char_case = char_case_e::lowercase,
.padd_with = padd_with_e::zeros,
.include_prefix = include_prefix_e::with_prefix,
}>(data.example_int) ); //example snprintf test
char const * const fmt{ "T%s %f %11.11x" };
int sz = snprintf(nullptr,0,fmt, data.example_string.c_str(), data.emaple_float, data.example_int );
string result;
result.resize(static_cast<size_t>(sz+1));
sz = snprintf(result.data(), result.size(),fmt, data.example_string.c_str(), data.emaple_float, data.example_int );
result.resize(static_cast<size_t>(sz));there are predefined cmake workflows to test
- cmake --workflow --preset="clang-19-release"
- cmake --workflow --preset="clang-19-libc++release"
- cmake --workflow --preset="clang-18-release"
- cmake --workflow --preset="clang-18-libc++release"
- cmake --workflow --preset="gcc-14-release"
- cmake --workflow --preset="gcc-13-release"
If you think you have found a bug, please file an issue via issue submission form. Include the relevant information to reproduce the bug for example as static_assert( expression ), if it is important also the compiler version and target architecture. Feature requests and contributions can be filed as issues or pull requests.
This library is available to anybody free of charge, under the terms of MIT License (see LICENSE.md).