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Diffstat (limited to 'libbutl/timestamp.hxx')
| -rw-r--r-- | libbutl/timestamp.hxx | 179 |
1 files changed, 179 insertions, 0 deletions
diff --git a/libbutl/timestamp.hxx b/libbutl/timestamp.hxx new file mode 100644 index 0000000..2714a0d --- /dev/null +++ b/libbutl/timestamp.hxx @@ -0,0 +1,179 @@ +// file : libbutl/timestamp.hxx -*- C++ -*- +// license : MIT; see accompanying LICENSE file + +#pragma once + +#include <iosfwd> +#include <string> +#include <chrono> + +#include <libbutl/export.hxx> + +namespace butl +{ + // On all three main platforms that we target (GNU/Linux, Windows (both + // VC++ and GCC/MinGW64), and MacOS X) with recent C++ runtimes, + // system_clock has nanoseconds resolution and counts from the UNIX + // epoch. The latter is important since struct stat also returns times + // based on UNIX epoch. + // + // The underlying type for nanoseconds duration is signed integer type + // of at least 64 bits (currently int64_t, available as duration::rep). + // Because it is signed, we will overflow in year 2262 but by then the + // underlying type will most likely have changed to something larger + // than 64-bit. + // + // So to support other platforms that could possibly use a different + // system_clock resolutions (e.g., microseconds), we actually not going + // to assume anywhere (except perhaps timestamp.cxx) that we are dealing + // with nanoseconds or the 64-bit underlying type. + // + using std::chrono::system_clock; + + // Note that the default-initialized timestamp has the timestamp_nonexistent + // value. + // + using timestamp = system_clock::time_point; + using duration = system_clock::duration; + + // Generally-useful special values. + // + // Note that unknown is less than nonexistent which in turn is less than + // unreal and all of them are less than any non-special value (strictly + // speaking unreal is no greater (older) than any real value). + // + const timestamp::rep timestamp_unknown_rep = -1; + const timestamp timestamp_unknown = timestamp (duration (-1)); + const timestamp::rep timestamp_nonexistent_rep = 0; + const timestamp timestamp_nonexistent = timestamp (duration (0)); + const timestamp::rep timestamp_unreal_rep = 1; + const timestamp timestamp_unreal = timestamp (duration (1)); + + // Print human-readable representation of the timestamp. + // + // By default the timestamp is converted by localtime_r() to the local + // timezone, so tzset() from <time.h> should be called prior to using the + // corresponding operator or the to_stream() function (normally from main() + // or equivalent). + // + // The format argument in the to_stream() function is the put_time() format + // string except that it also supports the nanoseconds conversion specifier + // in the form %[<d>N] where <d> is the optional single delimiter character, + // for example '.'. If the nanoseconds part is 0, then it is not printed + // (nor the delimiter character). Otherwise, if necessary, the nanoseconds + // part is padded to 9 characters with leading zeros. + // + // The special argument in the to_stream() function indicates whether the + // special timestamp_{unknown,nonexistent,unreal} values should be printed + // as '<unknown>', '<nonexistent>', and '<unreal>', respectively. + // + // The local argument in the to_stream() function indicates whether to use + // localtime_r() or gmtime_r(). + // + // Note also that these operators/function may throw std::system_error. + // + // Finally, padding is not fully supported by these operators/function. They + // throw runtime_error if nanoseconds conversion specifier is present and + // the stream's width field has been set to non-zero value before the call. + // + // Potential improvements: + // - add flag to to_stream() to use + // - support %[<d>U] (microseconds) and %[<d>M] (milliseconds). + // - make to_stream() a manipulator, similar to put_time() + // - support %(N) version for non-optional printing + // - support for suffix %[<d>N<s>], for example %[N nsec] + // + LIBBUTL_SYMEXPORT std::ostream& + to_stream (std::ostream&, + const timestamp&, + const char* format, + bool special, + bool local); + + // Same as above, but provide the result as a string. Note that it is + // implemented via to_stream() and std::ostringstream. + // + LIBBUTL_SYMEXPORT std::string + to_string (const timestamp&, + const char* format, + bool special, + bool local); + + inline std::ostream& + operator<< (std::ostream& os, const timestamp& ts) + { + return to_stream (os, ts, "%Y-%m-%d %H:%M:%S%[.N]", true, true); + } + + // Print human-readable representation of the duration. + // + LIBBUTL_SYMEXPORT std::ostream& + to_stream (std::ostream&, const duration&, bool nanoseconds); + + // Same as above, but provide the result as a string. Note that it is + // implemented via to_stream() and std::ostringstream. + // + LIBBUTL_SYMEXPORT std::string + to_string (const duration&, bool nanoseconds); + + inline std::ostream& + operator<< (std::ostream& os, const duration& d) + { + return to_stream (os, d, true); + } + + // Parse human-readable representation of the timestamp. + // + // The format argument is the strptime() format string except that it also + // supports the fraction of a second specifier in the form %[<d><f>], where + // <d> is the optional single delimiter character, for example '.', and <f> + // is one of the 'N', 'U', 'M' characters, denoting nanoseconds, + // microseconds and milliseconds, respectively. + // + // The delimiter <d> is mandatory. If no such character is encountered at + // the corresponding position of the input string, the function behaves as + // if no %[] specifier were provided. Only single %[] specifier in the + // format string is currently supported. + // + // If the delimiter is present, then it should be followed by 9 (N), 6 (U), + // or 3 (M) digit value padded with leading zeros if necessary. + // + // If the local argument is true, then the input is assume to be local time + // and the result is returned as local time as well. Otherwise, UCT is used + // in both cases. + // + // If the end argument is not NULL, then it points to the first character + // that was not parsed. Otherwise, throw invalid_argument in case of any + // unparsed characters. + // + // Throw std::system_error on input/format mismatch and underlying time + // conversion function failures. + // + // Note that internally from_string() calls strptime(), which behaves + // according to the process' C locale (set with std::setlocale()) and not + // the C++ locale (set with std::locale::global()). However the behaviour + // can be affected by std::locale::global() as well, as it itself calls + // std::setlocale() for the locale with a name. + // + // Potential improvements: + // - support %() version for non-optional component but with optional + // delimiter + // - ability to parse local, return UTC and vice-versa + // - handle timezone parsing + // + LIBBUTL_SYMEXPORT timestamp + from_string (const char* input, + const char* format, + bool local, + const char** end = nullptr); + + // Rebase a time point from UNIX epoch to midnight in the local time zone + // (so the returned duration is always less than 24 hours). + // + // Specifically, convert the time point from Epoch to the local time and + // return the time elapsed since midnight. Throw std::system_error on + // underlying time conversion function failures. + // + LIBBUTL_SYMEXPORT duration + daytime (timestamp); +} |