libpqxx  7.8.0
strconv.hxx
1 /* String conversion definitions.
2  *
3  * DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/stringconv instead.
4  *
5  * Copyright (c) 2000-2023, Jeroen T. Vermeulen.
6  *
7  * See COPYING for copyright license. If you did not receive a file called
8  * COPYING with this source code, please notify the distributor of this
9  * mistake, or contact the author.
10  */
11 #ifndef PQXX_H_STRCONV
12 #define PQXX_H_STRCONV
13 
14 #if !defined(PQXX_HEADER_PRE)
15 # error "Include libpqxx headers as <pqxx/header>, not <pqxx/header.hxx>."
16 #endif
17 
18 #include <algorithm>
19 #include <cstring>
20 #include <limits>
21 #include <sstream>
22 #include <stdexcept>
23 #include <typeinfo>
24 
25 #if __has_include(<charconv>)
26 # include <charconv>
27 #endif
28 
29 #if defined(PQXX_HAVE_RANGES) && __has_include(<ranges>)
30 # include <ranges>
31 #endif
32 
33 #include "pqxx/except.hxx"
34 #include "pqxx/util.hxx"
35 #include "pqxx/zview.hxx"
36 
37 
38 namespace pqxx::internal
39 {
41 PQXX_LIBEXPORT std::string demangle_type_name(char const[]);
42 } // namespace pqxx::internal
43 
44 
45 namespace pqxx
46 {
71 
73 
81 template<typename TYPE>
82 std::string const type_name{internal::demangle_type_name(typeid(TYPE).name())};
83 
84 
86 
92 template<typename TYPE, typename ENABLE = void> struct nullness
93 {
95  static bool has_null;
96 
98  static bool always_null;
99 
101  static bool is_null(TYPE const &value);
102 
104 
109  [[nodiscard]] static TYPE null();
110 };
111 
112 
114 template<typename TYPE> struct no_null
115 {
117 
127  static constexpr bool has_null = false;
128 
130 
133  static constexpr bool always_null = false;
134 
136 
140  [[nodiscard]] static constexpr bool is_null(TYPE const &) noexcept
141  {
142  return false;
143  }
144 };
145 
146 
148 
154 template<typename TYPE> struct string_traits
155 {
157 
160  static constexpr bool converts_to_string{false};
161 
163 
166  static constexpr bool converts_from_string{false};
167 
169 
188  [[nodiscard]] static inline zview
189  to_buf(char *begin, char *end, TYPE const &value);
190 
192  /* @warning A null value has no string representation. Do not pass a null.
193  *
194  * Writes value's string representation into the buffer, starting exactly at
195  * @c begin, and ensuring a trailing zero. Returns the address just beyond
196  * the trailing zero, so the caller could use it as the @c begin for another
197  * call to @c into_buf writing a next value.
198  */
199  static inline char *into_buf(char *begin, char *end, TYPE const &value);
200 
202 
207  [[nodiscard]] static inline TYPE from_string(std::string_view text);
208 
209  // C++20: Can we make these all constexpr?
211 
215  [[nodiscard]] static inline std::size_t
216  size_buffer(TYPE const &value) noexcept;
217 
218  // TODO: Move is_unquoted_string into the traits after all?
219 };
220 
221 
223 
239 template<typename TYPE> [[noreturn]]
241 
242 
244 
249 template<typename TYPE> struct forbidden_conversion
250 {
251  static constexpr bool converts_to_string{false};
252  static constexpr bool converts_from_string{false};
253  [[noreturn]] static zview to_buf(char *, char *, TYPE const &)
254  { oops_forbidden_conversion<TYPE>(); }
255  [[noreturn]] static char *into_buf(char *, char *, TYPE const &)
256  { oops_forbidden_conversion<TYPE>(); }
257  [[noreturn]] static TYPE from_string(std::string_view)
258  { oops_forbidden_conversion<TYPE>(); }
259  [[noreturn]] static std::size_t size_buffer(TYPE const &) noexcept
260  { oops_forbidden_conversion<TYPE>(); }
261 };
262 
263 
265 
281 template<> struct string_traits<char> : forbidden_conversion<char> {};
282 
283 
284 
286 
300 template<>
301 struct string_traits<unsigned char> : forbidden_conversion<unsigned char> {};
302 
303 
304 
306 
320 template<>
321 struct string_traits<signed char> : forbidden_conversion<signed char> {};
322 
323 
324 
326 
331 template<>
332 struct string_traits<std::byte> : forbidden_conversion<std::byte> {};
333 
334 
336 template<typename ENUM>
337 struct nullness<ENUM, std::enable_if_t<std::is_enum_v<ENUM>>> : no_null<ENUM>
338 {};
339 
340 
341 // C++20: Concepts for "converts from string" & "converts to string."
342 } // namespace pqxx
343 
344 
345 namespace pqxx::internal
346 {
348 
357 template<typename ENUM> struct enum_traits
358 {
359  using impl_type = std::underlying_type_t<ENUM>;
361 
362  static constexpr bool converts_to_string{true};
363  static constexpr bool converts_from_string{true};
364 
365  [[nodiscard]] static constexpr zview
366  to_buf(char *begin, char *end, ENUM const &value)
367  {
368  return impl_traits::to_buf(begin, end, to_underlying(value));
369  }
370 
371  static constexpr char *into_buf(char *begin, char *end, ENUM const &value)
372  {
373  return impl_traits::into_buf(begin, end, to_underlying(value));
374  }
375 
376  [[nodiscard]] static ENUM from_string(std::string_view text)
377  {
378  return static_cast<ENUM>(impl_traits::from_string(text));
379  }
380 
381  [[nodiscard]] static std::size_t size_buffer(ENUM const &value) noexcept
382  {
383  return impl_traits::size_buffer(to_underlying(value));
384  }
385 
386 private:
387  // C++23: Replace with std::to_underlying.
388  static constexpr impl_type to_underlying(ENUM const &value) noexcept
389  {
390  return static_cast<impl_type>(value);
391  }
392 };
393 } // namespace pqxx::internal
394 
395 
396 // We used to inline type_name<ENUM>, but this triggered a "double free" error
397 // on program exit, when libpqxx was built as a shared library on Debian with
398 // gcc 12.
399 
401 
412 #define PQXX_DECLARE_ENUM_CONVERSION(ENUM) \
413  template<> struct string_traits<ENUM> : pqxx::internal::enum_traits<ENUM> \
414  {}; \
415  template<> inline std::string_view const type_name<ENUM> { #ENUM }
416 
417 
418 namespace pqxx
419 {
421 
433 template<typename TYPE>
434 [[nodiscard]] inline TYPE from_string(std::string_view text)
435 {
437 }
438 
439 
441 
447 template<>
448 [[nodiscard]] inline std::string_view from_string(std::string_view text)
449 {
450  return text;
451 }
452 
453 
455 
462 template<typename T> inline void from_string(std::string_view text, T &value)
463 {
464  value = from_string<T>(text);
465 }
466 
467 
469 
474 template<typename TYPE> inline std::string to_string(TYPE const &value);
475 
476 
478 
485 template<typename... TYPE>
486 [[nodiscard]] inline std::vector<std::string_view>
487 to_buf(char *here, char const *end, TYPE... value)
488 {
489  return {[&here, end](auto v) {
490  auto begin = here;
491  here = string_traits<decltype(v)>::into_buf(begin, end, v);
492  // Exclude the trailing zero out of the string_view.
493  auto len{static_cast<std::size_t>(here - begin) - 1};
494  return std::string_view{begin, len};
495  }(value)...};
496 }
497 
499 
502 template<typename TYPE>
503 inline void into_string(TYPE const &value, std::string &out);
504 
505 
507 template<typename TYPE>
508 [[nodiscard]] inline constexpr bool is_null(TYPE const &value) noexcept
509 {
510  return nullness<strip_t<TYPE>>::is_null(value);
511 }
512 
513 
515 
518 template<typename... TYPE>
519 [[nodiscard]] inline std::size_t size_buffer(TYPE const &...value) noexcept
520 {
521  return (string_traits<strip_t<TYPE>>::size_buffer(value) + ...);
522 }
523 
524 
526 
532 template<typename TYPE> inline constexpr bool is_sql_array{false};
533 
534 
536 
548 template<typename TYPE> inline constexpr bool is_unquoted_safe{false};
549 
550 
552 template<typename T> inline constexpr char array_separator{','};
553 
554 
556 
563 template<typename TYPE> inline constexpr format param_format(TYPE const &)
564 {
565  return format::text;
566 }
567 
568 
570 
579 template<typename TYPE>
580 inline zview generic_to_buf(char *begin, char *end, TYPE const &value)
581 {
582  using traits = string_traits<TYPE>;
583  // The trailing zero does not count towards the zview's size, so subtract 1
584  // from the result we get from into_buf().
585  if (is_null(value))
586  return {};
587  else
588  return {begin, traits::into_buf(begin, end, value) - begin - 1};
589 }
590 
591 
592 #if defined(PQXX_HAVE_CONCEPTS)
594 
600 template<class TYPE>
601 concept binary = std::ranges::contiguous_range<TYPE> and
602  std::is_same_v<strip_t<value_type<TYPE>>, std::byte>;
603 #endif
605 } // namespace pqxx
606 
607 
608 #include "pqxx/internal/conversions.hxx"
609 #endif
The home of all libpqxx classes, functions, templates, etc.
Definition: array.hxx:33
std::string const type_name
A human-readable name for a type, used in error messages and such.
Definition: strconv.hxx:82
void into_string(TYPE const &value, std::string &out)
Convert a value to a readable string that PostgreSQL will understand.
std::remove_cv_t< std::remove_reference_t< TYPE > > strip_t
Remove any constness, volatile, and reference-ness from a type.
Definition: types.hxx:91
std::vector< std::string_view > to_buf(char *here, char const *end, TYPE... value)
Convert multiple values to strings inside a single buffer.
Definition: strconv.hxx:487
constexpr char array_separator
Element separator between SQL array elements of this type.
Definition: strconv.hxx:552
constexpr bool is_unquoted_safe
Can we use this type in arrays and composite types without quoting them?
Definition: strconv.hxx:548
std::size_t size_buffer(TYPE const &...value) noexcept
Estimate how much buffer space is needed to represent values as a string.
Definition: strconv.hxx:519
void oops_forbidden_conversion() noexcept
Nonexistent function to indicate a disallowed type conversion.
constexpr bool is_null(TYPE const &value) noexcept
Is value null?
Definition: strconv.hxx:508
zview generic_to_buf(char *begin, char *end, TYPE const &value)
Implement string_traits<TYPE>::to_buf by calling into_buf.
Definition: strconv.hxx:580
constexpr format param_format(TYPE const &)
What's the preferred format for passing non-null parameters of this type?
Definition: strconv.hxx:563
constexpr bool is_sql_array
Does this type translate to an SQL array?
Definition: strconv.hxx:532
std::string to_string(field const &value)
Convert a field to a string.
Definition: result.cxx:548
T from_string(field const &value)
Convert a field's value to type T.
Definition: field.hxx:520
format
Format code: is data text or binary?
Definition: types.hxx:81
Internal items for libpqxx' own use. Do not use these yourself.
Definition: composite.hxx:84
std::string demangle_type_name(char const[])
Attempt to demangle std::type_info::name() to something human-readable.
Definition: strconv.cxx:230
Traits describing a type's "null value," if any.
Definition: strconv.hxx:93
static bool is_null(TYPE const &value)
Is value a null?
static bool has_null
Does this type have a null value?
Definition: strconv.hxx:95
static bool always_null
Is this type always null?
Definition: strconv.hxx:98
Nullness traits describing a type which does not have a null value.
Definition: strconv.hxx:115
static constexpr bool always_null
Are all values of this type null?
Definition: strconv.hxx:133
static constexpr bool has_null
Does TYPE have a "built-in null value"?
Definition: strconv.hxx:127
static constexpr bool is_null(TYPE const &) noexcept
Does a given value correspond to an SQL null value?
Definition: strconv.hxx:140
Traits class for use in string conversions.
Definition: strconv.hxx:155
static std::size_t size_buffer(TYPE const &value) noexcept
Estimate how much buffer space is needed to represent value.
static zview to_buf(char *begin, char *end, TYPE const &value)
Return a string_view representing value, plus terminating zero.
static TYPE from_string(std::string_view text)
Parse a string representation of a TYPE value.
Definition: strconv.cxx:740
static constexpr bool converts_to_string
Is conversion from TYPE to strings supported?
Definition: strconv.hxx:160
static char * into_buf(char *begin, char *end, TYPE const &value)
Write value's string representation into buffer at begin.
static constexpr bool converts_from_string
Is conversion from string_view to TYPE supported?
Definition: strconv.hxx:166
String traits for a forbidden type conversion.
Definition: strconv.hxx:250
static TYPE from_string(std::string_view)
Definition: strconv.hxx:257
static std::size_t size_buffer(TYPE const &) noexcept
Definition: strconv.hxx:259
static zview to_buf(char *, char *, TYPE const &)
Definition: strconv.hxx:253
static char * into_buf(char *, char *, TYPE const &)
Definition: strconv.hxx:255
Helper class for defining enum conversions.
Definition: strconv.hxx:358
static std::size_t size_buffer(ENUM const &value) noexcept
Definition: strconv.hxx:381
static constexpr zview to_buf(char *begin, char *end, ENUM const &value)
Definition: strconv.hxx:366
static constexpr char * into_buf(char *begin, char *end, ENUM const &value)
Definition: strconv.hxx:371
static constexpr bool converts_from_string
Definition: strconv.hxx:363
std::underlying_type_t< ENUM > impl_type
Definition: strconv.hxx:359
static ENUM from_string(std::string_view text)
Definition: strconv.hxx:376
static constexpr bool converts_to_string
Definition: strconv.hxx:362
Marker-type wrapper: zero-terminated std::string_view.
Definition: zview.hxx:38