libpqxx
The C++ client library for PostgreSQL
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strconv.hxx
1/* String conversion definitions.
2 *
3 * DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/stringconv instead.
4 *
5 * Copyright (c) 2000-2024, 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 <charconv>
20#include <cstring>
21#include <limits>
22#include <sstream>
23#include <stdexcept>
24#include <typeinfo>
25
26// C++20: Assume support.
27#if __has_include(<ranges>)
28# include <ranges>
29#endif
30
31#include "pqxx/except.hxx"
32#include "pqxx/util.hxx"
33#include "pqxx/zview.hxx"
34
35
36namespace pqxx::internal
37{
39PQXX_LIBEXPORT std::string demangle_type_name(char const[]);
40} // namespace pqxx::internal
41
42
43namespace pqxx
44{
69
71
79template<typename TYPE>
80std::string const type_name{internal::demangle_type_name(typeid(TYPE).name())};
81
82
84
90template<typename TYPE, typename ENABLE = void> struct nullness
91{
93 static bool has_null;
94
96 static bool always_null;
97
99 static bool is_null(TYPE const &value);
100
102
107 [[nodiscard]] static TYPE null();
108};
109
110
112template<typename TYPE> struct no_null
113{
115
125 static constexpr bool has_null = false;
126
128
131 static constexpr bool always_null = false;
132
134
138 [[nodiscard]] static constexpr bool is_null(TYPE const &) noexcept
139 {
140 return false;
141 }
142};
143
144
146
152template<typename TYPE> struct string_traits
153{
155
158 static constexpr bool converts_to_string{false};
159
161
164 static constexpr bool converts_from_string{false};
165
167
186 [[nodiscard]] static inline zview
187 to_buf(char *begin, char *end, TYPE const &value);
188
190 /* @warning A null value has no string representation. Do not pass a null.
191 *
192 * Writes value's string representation into the buffer, starting exactly at
193 * @c begin, and ensuring a trailing zero. Returns the address just beyond
194 * the trailing zero, so the caller could use it as the @c begin for another
195 * call to @c into_buf writing a next value.
196 */
197 static inline char *into_buf(char *begin, char *end, TYPE const &value);
198
200
205 [[nodiscard]] static inline TYPE from_string(std::string_view text);
206
207 // C++20: Can we make these all constexpr?
209
213 [[nodiscard]] static inline std::size_t
214 size_buffer(TYPE const &value) noexcept;
215
216 // TODO: Move is_unquoted_string into the traits after all?
217};
218
219
221
237template<typename TYPE> [[noreturn]] void oops_forbidden_conversion() noexcept;
238
239
241
246template<typename TYPE> struct forbidden_conversion
247{
248 static constexpr bool converts_to_string{false};
249 static constexpr bool converts_from_string{false};
250 [[noreturn]] static zview to_buf(char *, char *, TYPE const &)
251 {
252 oops_forbidden_conversion<TYPE>();
253 }
254 [[noreturn]] static char *into_buf(char *, char *, TYPE const &)
255 {
256 oops_forbidden_conversion<TYPE>();
257 }
258 [[noreturn]] static TYPE from_string(std::string_view)
259 {
260 oops_forbidden_conversion<TYPE>();
261 }
262 [[noreturn]] static std::size_t size_buffer(TYPE const &) noexcept
263 {
264 oops_forbidden_conversion<TYPE>();
265 }
266};
267
268
270
285template<> struct string_traits<char> : forbidden_conversion<char>
286{};
287
288
290
303template<>
304struct string_traits<unsigned char> : forbidden_conversion<unsigned char>
305{};
306
307
309
322template<>
323struct string_traits<signed char> : forbidden_conversion<signed char>
324{};
325
326
328
333template<> struct string_traits<std::byte> : forbidden_conversion<std::byte>
334{};
335
336
338template<typename ENUM>
339struct nullness<ENUM, std::enable_if_t<std::is_enum_v<ENUM>>> : no_null<ENUM>
340{};
341
342
343// C++20: Concepts for "converts from string" & "converts to string."
344} // namespace pqxx
345
346
347namespace pqxx::internal
348{
350
359template<typename ENUM> struct enum_traits
360{
361 using impl_type = std::underlying_type_t<ENUM>;
363
364 static constexpr bool converts_to_string{true};
365 static constexpr bool converts_from_string{true};
366
367 [[nodiscard]] static constexpr zview
368 to_buf(char *begin, char *end, ENUM const &value)
369 {
370 return impl_traits::to_buf(begin, end, to_underlying(value));
371 }
372
373 static constexpr char *into_buf(char *begin, char *end, ENUM const &value)
374 {
375 return impl_traits::into_buf(begin, end, to_underlying(value));
376 }
377
378 [[nodiscard]] static ENUM from_string(std::string_view text)
379 {
380 return static_cast<ENUM>(impl_traits::from_string(text));
381 }
382
383 [[nodiscard]] static std::size_t size_buffer(ENUM const &value) noexcept
384 {
385 return impl_traits::size_buffer(to_underlying(value));
386 }
387
388private:
389 // C++23: Replace with std::to_underlying.
390 static constexpr impl_type to_underlying(ENUM const &value) noexcept
391 {
392 return static_cast<impl_type>(value);
393 }
394};
395} // namespace pqxx::internal
396
397
398// We used to inline type_name<ENUM>, but this triggered a "double free" error
399// on program exit, when libpqxx was built as a shared library on Debian with
400// gcc 12.
401
403
414#define PQXX_DECLARE_ENUM_CONVERSION(ENUM) \
415 template<> struct string_traits<ENUM> : pqxx::internal::enum_traits<ENUM> \
416 {}; \
417 template<> inline std::string_view const type_name<ENUM> \
418 { \
419 #ENUM \
420 }
421
422
423namespace pqxx
424{
426
438template<typename TYPE>
439[[nodiscard]] inline TYPE from_string(std::string_view text)
440{
442}
443
444
446
452template<>
453[[nodiscard]] inline std::string_view from_string(std::string_view text)
454{
455 return text;
456}
457
458
460
467template<typename T> inline void from_string(std::string_view text, T &value)
468{
469 value = from_string<T>(text);
470}
471
472
474
479template<typename TYPE> inline std::string to_string(TYPE const &value);
480
481
483
490template<typename... TYPE>
491[[nodiscard]] inline std::vector<std::string_view>
492to_buf(char *here, char const *end, TYPE... value)
493{
494 PQXX_ASSUME(here <= end);
495 return {[&here, end](auto v) {
496 auto begin = here;
497 here = string_traits<decltype(v)>::into_buf(begin, end, v);
498 // Exclude the trailing zero out of the string_view.
499 auto len{static_cast<std::size_t>(here - begin) - 1};
500 return std::string_view{begin, len};
501 }(value)...};
502}
503
505
508template<typename TYPE>
509inline void into_string(TYPE const &value, std::string &out);
510
511
513template<typename TYPE>
514[[nodiscard]] inline constexpr bool is_null(TYPE const &value) noexcept
515{
516 return nullness<strip_t<TYPE>>::is_null(value);
517}
518
519
521
524template<typename... TYPE>
525[[nodiscard]] inline std::size_t size_buffer(TYPE const &...value) noexcept
526{
527 return (string_traits<strip_t<TYPE>>::size_buffer(value) + ...);
528}
529
530
532
538template<typename TYPE> inline constexpr bool is_sql_array{false};
539
540
542
554template<typename TYPE> inline constexpr bool is_unquoted_safe{false};
555
556
558template<typename T> inline constexpr char array_separator{','};
559
560
562
569template<typename TYPE> inline constexpr format param_format(TYPE const &)
570{
571 return format::text;
572}
573
574
576
585template<typename TYPE>
586inline zview generic_to_buf(char *begin, char *end, TYPE const &value)
587{
588 using traits = string_traits<TYPE>;
589 // The trailing zero does not count towards the zview's size, so subtract 1
590 // from the result we get from into_buf().
591 if (is_null(value))
592 return {};
593 else
594 return {begin, traits::into_buf(begin, end, value) - begin - 1};
595}
596
597
598#if defined(PQXX_HAVE_CONCEPTS)
600
606template<class TYPE>
607concept binary = std::ranges::contiguous_range<TYPE> and
608 std::is_same_v<strip_t<value_type<TYPE>>, std::byte>;
609#endif
611} // namespace pqxx
612
613
614#include "pqxx/internal/conversions.hxx"
615#endif
Marker-type wrapper: zero-terminated std::string_view.
Definition zview.hxx:38
Internal items for libpqxx' own use. Do not use these yourself.
Definition encodings.cxx:33
std::string demangle_type_name(char const raw[])
Attempt to demangle std::type_info::name() to something human-readable.
Definition strconv.cxx:233
The home of all libpqxx classes, functions, templates, etc.
Definition array.cxx:27
std::string const type_name
A human-readable name for a type, used in error messages and such.
Definition strconv.hxx:80
void oops_forbidden_conversion() noexcept
Nonexistent function to indicate a disallowed type conversion.
PQXX_LIBEXPORT std::string to_string(field const &value)
Convert a field to a string.
Definition result.cxx:566
T from_string(field const &value)
Convert a field's value to type T.
Definition field.hxx:532
format
Format code: is data text or binary?
Definition types.hxx:68
String traits for a forbidden type conversion.
Definition strconv.hxx:247
Helper class for defining enum conversions.
Definition strconv.hxx:360
Nullness traits describing a type which does not have a null value.
Definition strconv.hxx:113
static constexpr bool always_null
Are all values of this type null?
Definition strconv.hxx:131
static constexpr bool has_null
Does TYPE have a "built-in null value"?
Definition strconv.hxx:125
static constexpr bool is_null(TYPE const &) noexcept
Does a given value correspond to an SQL null value?
Definition strconv.hxx:138
Traits describing a type's "null value," if any.
Definition strconv.hxx:91
static bool is_null(TYPE const &value)
Is value a null?
static TYPE null()
Return a null value.
static bool has_null
Does this type have a null value?
Definition strconv.hxx:93
static bool always_null
Is this type always null?
Definition strconv.hxx:96
Traits class for use in string conversions.
Definition strconv.hxx:153
static TYPE from_string(std::string_view text)
Parse a string representation of a TYPE value.
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 constexpr bool converts_to_string
Is conversion from TYPE to strings supported?
Definition strconv.hxx:158
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:164