mirror of
https://github.com/ashaduri/gsmartcontrol.git
synced 2026-09-26 13:55:34 +00:00
Refactored example_string_num.cpp into a test.
Fixed underflow detection for unsigned types in hz::string_is_numeric().
This commit is contained in:
Alexander Shaduri
@@ -18,12 +18,3 @@ target_sources(example_string_algo PRIVATE
|
||||
target_link_libraries(example_string_algo PRIVATE
|
||||
hz
|
||||
)
|
||||
|
||||
|
||||
add_executable(example_string_num)
|
||||
target_sources(example_string_num PRIVATE
|
||||
example_string_num.cpp
|
||||
)
|
||||
target_link_libraries(example_string_num PRIVATE
|
||||
hz
|
||||
)
|
||||
|
||||
@@ -1,194 +0,0 @@
|
||||
/******************************************************************************
|
||||
License: BSD Zero Clause License
|
||||
Copyright:
|
||||
(C) 2008 - 2021 Alexander Shaduri <ashaduri@gmail.com>
|
||||
******************************************************************************/
|
||||
/// \file
|
||||
/// \author Alexander Shaduri
|
||||
/// \ingroup hz_examples
|
||||
/// \weakgroup hz_examples
|
||||
/// @{
|
||||
|
||||
// disable libdebug, we don't link to it
|
||||
#undef HZ_USE_LIBDEBUG
|
||||
#define HZ_USE_LIBDEBUG 0
|
||||
// enable libdebug emulation through std::cerr
|
||||
#undef HZ_EMULATE_LIBDEBUG
|
||||
#define HZ_EMULATE_LIBDEBUG 1
|
||||
|
||||
// The first header should be then one we're testing, to avoid missing
|
||||
// header pitfalls.
|
||||
#include "hz/string_num.h"
|
||||
|
||||
#include <limits>
|
||||
#include <iostream>
|
||||
#include <cstdint>
|
||||
|
||||
#include "hz/main_tools.h"
|
||||
|
||||
|
||||
|
||||
/// Main function for the test
|
||||
int main()
|
||||
{
|
||||
return hz::main_exception_wrapper([]()
|
||||
{
|
||||
using namespace hz;
|
||||
|
||||
// int i = 0;
|
||||
// double d = 0;
|
||||
|
||||
// std::cerr << (string_is_numeric_nolocale<int>("-1", i) ? "true" : "false");
|
||||
// std::cerr << ", parsed: i=" << i << "\n";
|
||||
|
||||
|
||||
{
|
||||
int16_t int16_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("32768", int16_) ? "true" : "false"); // overflow, false
|
||||
std::cerr << "\n";
|
||||
|
||||
uint16_t uint16_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("65535", uint16_) ? "true" : "false"); // true
|
||||
std::cerr << "\n";
|
||||
|
||||
int32_t int32_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale(" 1.33", int32_) ? "true" : "false"); // strict, false
|
||||
std::cerr << "\n";
|
||||
|
||||
int32_t int32_2 = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("1.33", int32_2) ? "true" : "false"); // strict, false
|
||||
std::cerr << "\n";
|
||||
|
||||
uint32_t uint32_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("-1", uint32_) ? "true" : "false"); // underflow, false
|
||||
std::cerr << "\n";
|
||||
|
||||
int64_t int64_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("-1", int64_) ? "true" : "false"); // true
|
||||
std::cerr << "\n";
|
||||
|
||||
uint64_t uint64_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("1", uint64_) ? "true" : "false"); // true
|
||||
std::cerr << "\n";
|
||||
|
||||
int int_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("-1", int_) ? "true" : "false"); // true
|
||||
std::cerr << "\n";
|
||||
|
||||
unsigned int uint_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("-1", uint_) ? "true" : "false"); // underflow, false
|
||||
std::cerr << "\n";
|
||||
|
||||
long long_int_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("-1", long_int_) ? "true" : "false"); // true
|
||||
std::cerr << "\n";
|
||||
|
||||
unsigned long long_uint_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("-1", long_uint_) ? "true" : "false"); // underflow, false
|
||||
std::cerr << "\n";
|
||||
|
||||
char char_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("4", char_) ? "true" : "false"); // true
|
||||
std::cerr << "\n";
|
||||
|
||||
unsigned char uchar_ = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("315", uchar_) ? "true" : "false"); // overflow, false
|
||||
std::cerr << "\n";
|
||||
|
||||
signed char schar_2 = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("128", schar_2) ? "true" : "false"); // overflow, false
|
||||
std::cerr << "\n";
|
||||
|
||||
signed char schar_3 = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("-128", schar_3) ? "true" : "false"); // true
|
||||
std::cerr << "\n";
|
||||
|
||||
unsigned char uchar_2 = 0;
|
||||
std::cerr << (string_is_numeric_nolocale("128", uchar_2) ? "true" : "false"); // true
|
||||
std::cerr << "\n";
|
||||
|
||||
bool b = false;
|
||||
std::cerr << (string_is_numeric_nolocale("true", b) ? "true" : "false"); // true
|
||||
std::cerr << "\n";
|
||||
|
||||
}
|
||||
|
||||
|
||||
// std::cerr << (string_is_numeric_nolocale<int>("-1.3", i) ? "true" : "false");
|
||||
// std::cerr << ", parsed: i=" << i << "\n";
|
||||
|
||||
|
||||
{
|
||||
double d = 0;
|
||||
|
||||
std::cerr << (string_is_numeric_nolocale("-1.3", d) ? "true" : "false");
|
||||
std::cerr << ", parsed: d=" << d << "\n";
|
||||
|
||||
std::cerr << (string_is_numeric_nolocale(" inf", d) ? "true" : "false");
|
||||
std::cerr << ", parsed: d=" << d << "\n";
|
||||
|
||||
std::cerr << (string_is_numeric_nolocale("infinity", d) ? "true" : "false");
|
||||
std::cerr << ", parsed: d=" << d << "\n";
|
||||
|
||||
std::cerr << (string_is_numeric_nolocale("NAn", d) ? "true" : "false");
|
||||
std::cerr << ", parsed: d=" << d << "\n";
|
||||
|
||||
std::cerr << (string_is_numeric_nolocale("3.e+4", d) ? "true" : "false");
|
||||
std::cerr << ", parsed: d=" << d << "\n";
|
||||
|
||||
std::cerr << (string_is_numeric_nolocale("123 ", d) ? "true" : "false");
|
||||
std::cerr << ", parsed: d=" << d << "\n";
|
||||
|
||||
std::cerr << (string_is_numeric_nolocale("e+3", d) ? "true" : "false");
|
||||
std::cerr << ", parsed: d=" << d << "\n";
|
||||
}
|
||||
|
||||
|
||||
|
||||
{
|
||||
|
||||
// Note: suffixes are case-insensitive.
|
||||
// Long int and long double are differentiated by '.' in constant.
|
||||
|
||||
std::cerr << number_to_string_nolocale(true) << "\n"; // bool
|
||||
std::cerr << number_to_string_nolocale('a') << "\n"; // char
|
||||
std::cerr << number_to_string_nolocale(1.L) << "\n"; // long double
|
||||
std::cerr << number_to_string_nolocale(2L) << "\n"; // long int
|
||||
std::cerr << number_to_string_nolocale(6) << "\n"; // int
|
||||
|
||||
std::cerr << number_to_string_nolocale(3LL) << "\n"; // long long int
|
||||
std::cerr << number_to_string_nolocale(4ULL) << "\n"; // unsigned long long int
|
||||
|
||||
std::cerr << number_to_string_nolocale(5.f) << "\n"; // float
|
||||
std::cerr << number_to_string_nolocale(1.33) << "\n"; // double
|
||||
std::cerr << number_to_string_nolocale(2.123456789123456789123456789L) << "\n";
|
||||
|
||||
std::cerr << number_to_string_nolocale(std::numeric_limits<double>::quiet_NaN()) << "\n";
|
||||
std::cerr << number_to_string_nolocale(std::numeric_limits<float>::signaling_NaN()) << "\n";
|
||||
std::cerr << number_to_string_nolocale(std::numeric_limits<long double>::infinity()) << "\n";
|
||||
|
||||
std::cerr << number_to_string_nolocale(uint16_t(0x1133), 16) << "\n";
|
||||
std::cerr << number_to_string_nolocale(uint32_t(0x00001234), 16) << "\n";
|
||||
std::cerr << number_to_string_nolocale(uint64_t(0x00001234), 16) << "\n";
|
||||
std::cerr << number_to_string_nolocale(uint16_t(0), 16) << "\n";
|
||||
|
||||
std::cerr << number_to_string_nolocale(uint16_t(0xffff), 8) << "\n";
|
||||
std::cerr << number_to_string_nolocale(uint16_t(0), 8) << "\n";
|
||||
|
||||
// std::cerr << number_to_string_nolocale("abc", 8) << "\n";
|
||||
|
||||
// std::cerr << number_to_string_nolocale(uint16_t(0xffff), 2) << "\n"; // won't work
|
||||
// std::cerr << number_to_string_nolocale(uint16_t(0), 2) << "\n";
|
||||
|
||||
}
|
||||
|
||||
return EXIT_SUCCESS;
|
||||
});
|
||||
}
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
/// @}
|
||||
+30
-6
@@ -122,6 +122,18 @@ namespace hz {
|
||||
namespace internal {
|
||||
|
||||
|
||||
/// If a string starts with '-', stoul() and stoull() use unsigned wraparound rules
|
||||
/// for the return value, not returning "out of range". Detect this condition.
|
||||
inline bool string_starts_with_minus(const std::string& s, const std::locale& loc)
|
||||
{
|
||||
auto first_symbol = std::find_if(s.begin(), s.end(), [&](char c) {
|
||||
return !std::isspace(c, loc);
|
||||
});
|
||||
return first_symbol != s.end() && *first_symbol == '-';
|
||||
}
|
||||
|
||||
|
||||
|
||||
// Version for integral / floating point types
|
||||
template<typename T>
|
||||
bool string_is_numeric_impl_global_locale(const std::string& s, T& number, bool strict, [[maybe_unused]] int base, const std::locale& loc = std::locale())
|
||||
@@ -135,9 +147,14 @@ namespace internal {
|
||||
T value = T();
|
||||
|
||||
try {
|
||||
if constexpr(std::is_same_v<T, char> || std::is_same_v<T, unsigned char> || std::is_same_v<T, signed char>
|
||||
|| std::is_same_v<T, wchar_t> || std::is_same_v<T, char16_t> || std::is_same_v<T, char32_t>
|
||||
|| std::is_same_v<T, short> || std::is_same_v<T, int>) {
|
||||
if constexpr(std::is_same_v<T, char>
|
||||
|| std::is_same_v<T, unsigned char>
|
||||
|| std::is_same_v<T, signed char>
|
||||
|| std::is_same_v<T, wchar_t>
|
||||
|| std::is_same_v<T, char16_t>
|
||||
|| std::is_same_v<T, char32_t>
|
||||
|| std::is_same_v<T, short>
|
||||
|| std::is_same_v<T, int>) {
|
||||
int tmp = std::stoi(s, &num_read, base);
|
||||
if (tmp != static_cast<T>(tmp)) {
|
||||
return false; // out of range
|
||||
@@ -147,14 +164,21 @@ namespace internal {
|
||||
value = std::stol(s, &num_read, base);
|
||||
} else if constexpr(std::is_same_v<T, long long>) {
|
||||
value = std::stoll(s, &num_read, base);
|
||||
} else if constexpr(std::is_same_v<T, unsigned short> || std::is_same_v<T, unsigned int> ||
|
||||
std::is_same_v<T, unsigned long>) {
|
||||
} else if constexpr(std::is_same_v<T, unsigned short>
|
||||
|| std::is_same_v<T, unsigned int>
|
||||
|| std::is_same_v<T, unsigned long>) {
|
||||
if (string_starts_with_minus(s, loc)) {
|
||||
return false; // "out of range" for unsigned
|
||||
}
|
||||
unsigned long tmp = std::stoul(s, &num_read, base);
|
||||
if (tmp != static_cast<T>(tmp)) {
|
||||
return false; // out of range
|
||||
return false; // out of range for smaller type
|
||||
}
|
||||
value = static_cast<T>(tmp);
|
||||
} else if constexpr(std::is_same_v<T, unsigned long long>) {
|
||||
if (string_starts_with_minus(s, loc)) {
|
||||
return false; // "out of range" for unsigned
|
||||
}
|
||||
value = std::stoull(s, &num_read, base);
|
||||
} else if constexpr(std::is_same_v<T, float>) {
|
||||
value = std::stof(s, &num_read);
|
||||
|
||||
@@ -15,6 +15,7 @@ endif()
|
||||
add_library(hz_tests OBJECT)
|
||||
target_sources(hz_tests PRIVATE
|
||||
test_format_unit.cpp
|
||||
test_string_num.cpp
|
||||
)
|
||||
target_link_libraries(hz_tests PRIVATE
|
||||
hz
|
||||
|
||||
@@ -0,0 +1,220 @@
|
||||
/******************************************************************************
|
||||
License: BSD Zero Clause License
|
||||
Copyright:
|
||||
(C) 2008 - 2022 Alexander Shaduri <ashaduri@gmail.com>
|
||||
******************************************************************************/
|
||||
/// \file
|
||||
/// \author Alexander Shaduri
|
||||
/// \ingroup hz_tests
|
||||
/// \weakgroup hz_tests
|
||||
/// @{
|
||||
|
||||
// Catch2 v3
|
||||
//#include "catch2/catch_test_macros.hpp"
|
||||
|
||||
// Catch2 v2
|
||||
#include "catch2/catch.hpp"
|
||||
|
||||
// disable libdebug, we don't link to it
|
||||
#undef HZ_USE_LIBDEBUG
|
||||
#define HZ_USE_LIBDEBUG 0
|
||||
// enable libdebug emulation through std::cerr
|
||||
#undef HZ_EMULATE_LIBDEBUG
|
||||
#define HZ_EMULATE_LIBDEBUG 1
|
||||
|
||||
// The first header should be then one we're testing, to avoid missing
|
||||
// header pitfalls.
|
||||
#include "hz/string_num.h"
|
||||
|
||||
#include <limits>
|
||||
#include <cstdint>
|
||||
|
||||
#include "hz/main_tools.h"
|
||||
|
||||
|
||||
|
||||
TEST_CASE("NumericStrings", "[hz][parser]")
|
||||
{
|
||||
using namespace hz;
|
||||
|
||||
{
|
||||
int i = 10;
|
||||
REQUIRE(string_is_numeric_nolocale<int>("-1", i) == true);
|
||||
REQUIRE(i == -1);
|
||||
}
|
||||
{
|
||||
int i = 10;
|
||||
REQUIRE(string_is_numeric_nolocale<int>("-1.3", i) == false);
|
||||
REQUIRE(i == 10);
|
||||
}
|
||||
{
|
||||
int16_t int16_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("32768", int16_) == false); // overflow, false
|
||||
REQUIRE(int16_ == 10);
|
||||
|
||||
uint16_t uint16_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("65535", uint16_) == true);
|
||||
REQUIRE(uint16_ == 65535);
|
||||
|
||||
int32_t int32_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale(" 1.33", int32_) == false); // strict, false
|
||||
REQUIRE(int32_ == 10);
|
||||
|
||||
int32_t int32_2 = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("1.33", int32_2) == false); // strict, false
|
||||
REQUIRE(int32_2 == 10);
|
||||
|
||||
uint32_t uint32_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-1", uint32_) == false); // underflow, false
|
||||
REQUIRE(uint32_ == 10);
|
||||
|
||||
int64_t int64_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-1", int64_) == true);
|
||||
REQUIRE(int64_ == -1);
|
||||
|
||||
uint64_t uint64_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("1", uint64_) == true);
|
||||
REQUIRE(uint64_ == 1);
|
||||
|
||||
uint64_t uint64_2 = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-1", uint64_2) == false); // underflow
|
||||
REQUIRE(uint64_2 == 10);
|
||||
|
||||
uint64_t uint64_3 = 10;
|
||||
REQUIRE(string_is_numeric_nolocale(" 1", uint64_3) == false); // strict
|
||||
REQUIRE(uint64_3 == 10);
|
||||
|
||||
uint64_t uint64_4 = 10;
|
||||
REQUIRE(string_is_numeric_nolocale(" 1", uint64_4, false) == true); // ignore space
|
||||
REQUIRE(uint64_4 == 1);
|
||||
|
||||
int int_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-1", int_) == true);
|
||||
REQUIRE(int_ == -1);
|
||||
|
||||
unsigned int uint_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-1", uint_) == false); // underflow, false
|
||||
REQUIRE(uint_ == 10);
|
||||
|
||||
long long_int_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-1", long_int_) == true);
|
||||
REQUIRE(long_int_ == -1);
|
||||
|
||||
unsigned long long_uint_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-1", long_uint_) == false); // underflow, false
|
||||
REQUIRE(long_uint_ == 10);
|
||||
|
||||
char char_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("4", char_) == true);
|
||||
REQUIRE(char_ == 4);
|
||||
|
||||
unsigned char uchar_ = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("315", uchar_) == false); // overflow, false
|
||||
REQUIRE(uchar_ == 10);
|
||||
|
||||
unsigned char uchar_2 = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("128", uchar_2) == true);
|
||||
REQUIRE(uchar_2 == 128);
|
||||
|
||||
unsigned char uchar_3 = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-2", uchar_3) == false); // underflow
|
||||
REQUIRE(uchar_3 == 10);
|
||||
|
||||
signed char schar_2 = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("128", schar_2) == false); // overflow, false
|
||||
REQUIRE(schar_2 == 10);
|
||||
|
||||
signed char schar_3 = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-128", schar_3) == true);
|
||||
REQUIRE(schar_3 == -128);
|
||||
|
||||
bool b = false;
|
||||
REQUIRE(string_is_numeric_nolocale("true", b) == true);
|
||||
REQUIRE(b == true);
|
||||
}
|
||||
{
|
||||
const double eps = std::numeric_limits<double>::epsilon(); // it will do
|
||||
|
||||
double d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-1.3", d) == true);
|
||||
REQUIRE(std::abs(-1.3 - d) <= eps);
|
||||
|
||||
d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale(" inf", d) == false);
|
||||
REQUIRE(std::abs(10. - d) <= eps);
|
||||
|
||||
d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale(" inf", d, false) == true); // non-strict
|
||||
REQUIRE(std::isinf(d));
|
||||
|
||||
d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("infinity", d) == true);
|
||||
REQUIRE(std::isinf(d));
|
||||
|
||||
d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("NAn", d) == true);
|
||||
REQUIRE(std::isnan(d));
|
||||
|
||||
d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("3.e+4", d) == true);
|
||||
REQUIRE(std::abs(3e4 - d) <= eps);
|
||||
|
||||
d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("-3E4", d) == true);
|
||||
REQUIRE(std::abs(-3e4 - d) <= eps);
|
||||
|
||||
d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("123 ", d) == false); // strict
|
||||
REQUIRE(std::abs(10 - d) <= eps);
|
||||
|
||||
d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("123 ", d, false) == true); // non-strict
|
||||
REQUIRE(std::abs(123 - d) <= eps);
|
||||
|
||||
d = 10;
|
||||
REQUIRE(string_is_numeric_nolocale("e+3", d) == false);
|
||||
REQUIRE(std::abs(10 - d) <= eps);
|
||||
}
|
||||
{
|
||||
|
||||
// Note: suffixes are case-insensitive.
|
||||
// Long int and long double are differentiated by '.' in constant.
|
||||
|
||||
REQUIRE(number_to_string_nolocale(true) == "true"); // bool
|
||||
REQUIRE(number_to_string_nolocale('a') == "97"); // char
|
||||
REQUIRE(number_to_string_nolocale(1.L) == "1"); // long double
|
||||
REQUIRE(number_to_string_nolocale(2L) == "2"); // long int
|
||||
REQUIRE(number_to_string_nolocale(6) == "6"); // int
|
||||
|
||||
REQUIRE(number_to_string_nolocale(3LL) == "3"); // long long int
|
||||
REQUIRE(number_to_string_nolocale(4ULL) == "4"); // unsigned long long int
|
||||
|
||||
REQUIRE(number_to_string_nolocale(5.F) == "5"); // float
|
||||
REQUIRE(number_to_string_nolocale(1.33) == "1.33"); // double
|
||||
REQUIRE(number_to_string_nolocale(2.123456789123456789123456789L) == "2.123456789123456789");
|
||||
|
||||
REQUIRE(number_to_string_nolocale(std::numeric_limits<double>::quiet_NaN()) == "nan");
|
||||
REQUIRE(number_to_string_nolocale(std::numeric_limits<float>::signaling_NaN()) == "nan");
|
||||
REQUIRE(number_to_string_nolocale(std::numeric_limits<long double>::infinity()) == "inf");
|
||||
REQUIRE(number_to_string_nolocale(-std::numeric_limits<long double>::infinity()) == "-inf");
|
||||
|
||||
REQUIRE(number_to_string_nolocale(uint16_t(0x1133), 16) == "0x1133");
|
||||
REQUIRE(number_to_string_nolocale(uint32_t(0x00001234), 16) == "0x00001234");
|
||||
REQUIRE(number_to_string_nolocale(uint64_t(0x00001234), 16) == "0x0000000000001234");
|
||||
REQUIRE(number_to_string_nolocale(uint16_t(0), 16) == "0x0000");
|
||||
|
||||
REQUIRE(number_to_string_nolocale(uint16_t(0xffff), 8) == "0177777");
|
||||
REQUIRE(number_to_string_nolocale(uint16_t(0), 8) == "00");
|
||||
|
||||
REQUIRE(number_to_string_nolocale(uint16_t(0xffff), 2) == "65535");
|
||||
REQUIRE(number_to_string_nolocale(uint16_t(0), 2) == "0");
|
||||
|
||||
}
|
||||
}
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
|
||||
/// @}
|
||||
Reference in New Issue
Block a user