/doc/time.datetime.html

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  4. <title>PTypes: date/time: datetime</title>
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  10. <p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a> 
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  13. <p class="hpath"><a href="index.html">Top</a>: <a href="basic.html">Basic types</a>: 
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  14. <a href="time.html">Date/time</a>: Datetime type</p>
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  15. <blockquote> 
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  16. <pre class="lang">#include &lt;ptime.h&gt;
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  17. 

  18. typedef large datetime;
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  20. datetime  now(bool utc = true);
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  21. int       days(datetime d);
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  22. int       msecs(datetime d);
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  23. datetime  mkdt(int days, int msecs);
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  24. bool      isvalid(datetime d);
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  25. void      tzupdate();
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  26. int       tzoffset();
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  27. string    dttostring(datetime d, const char* fmt);
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  28. string    nowstring(const char* fmt, bool utc = true);
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  29. datetime  utodatetime(time_t u);</pre>
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  30. </blockquote>
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  31. <p><span class="def">datetime now(bool utc = true)</span> returns the current 
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  32. date/time. The returned value can be either the local time or the Universal Coordinated 
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  33. Time (UTC, aka GMT), depending on the parameter <span class="lang">utc</span>. 
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  34. It is recommended to manipulate with the UTC time internally in your application 
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  35. whenever possible (f.ex. when it's not needed to display the time to the user), 
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  36. since in many countries the local time may be automatically adjusted when entering 
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  37. or leaving the daylight saving period, which may confuse your application. On 
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  38. the contrary, the UTC time never changes. That's why all modern operating systems 
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  39. rely on the UTC time internally. (See also <span class="lang">tzupdate()</span> 
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  40. below for additional notes).</p>
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  41. <p><span class="def">int days(datetime d)</span> returns the number of days since 
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  42. the beginning of the calendar contained in the <span class="lang">datetime</span> 
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  43. value <span class="lang">d</span>.</p>
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  44. <p><span class="def">int msecs(datetime d)</span> returns the number of milliseconds 
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  45. since midnight contained in the <span class="lang">datetime</span> value <span class="lang">d</span>.</p>
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  46. <p><span class="def">datetime mkdt(int days, int msecs)</span> calculates the 
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  47. datetime value from <span class="lang">days</span> and <span class="lang">msecs</span> 
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  48. parameters. <span class="lang">Days</span> is the number of days since the beginning 
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  49. of the calendar, and <span class="lang">msecs</span> is the number of milliseconds 
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  50. since midnight. No checks are made for validity of these values. There exists 
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  51. an easier way to build a datetime value using <span class="lang">encodedate()</span> 
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  52. and <span class="lang">encodetime()</span> functions having the year, month and 
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  53. day numbers, as well as (not necessarily) the hour, minute, second and millisecond 
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  54. values.</p>
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  55. <p><span class="def">bool isvalid(datetime d)</span> checks a <span class="lang">datetime</span> 
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  56. value for validity. The value of <span class="lang">d</span> is valid if it holds 
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  57. a time stamp between 01/01/0001 and 12/31/9999.</p>
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  58. <p><span class="def">void tzupdate()</span> updates the internal timezone information, 
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  59. which affects the value of local time returned by <span class="lang">now()</span> 
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  60. and <span class="lang">nowstring()</span>. If your application is supposed to 
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  61. be running infinitely (e.g. if it's a network daemon), you might want to update 
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  62. the internal timezone information from time to time in order to return correct 
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  63. local time to the user on DST adjustment days. Depending on the precision of local 
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  64. time you wish to show to the user, you can call this function, for example, every 
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  65. minute or every hour. Without this, the local time may become incorrect at the 
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  66. moment of DST adjustment, which occurs twice a year in most countries.</p>
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  67. <p><span class="def">int tzoffset()</span> returns the time zone offset in minutes. 
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  68. This value is negative in the West. Multiplying this value by 60000 (i.e. the 
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  69. offset in milliseconds) and adding it to the UTC <span class="lang">datetime</span> 
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  70. value will give the local time.</p>
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  71. <p><span class="def">string dttostring(datetime d, const char* fmt)</span> converts 
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  72. a <span class="lang">datetime</span> value to string representation as specified 
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  73. by <span class="lang">fmt</span>. The syntax of the format specifier is the same 
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  74. as for <span class="lang">strftime()</span> (please, refer to the corresponding 
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  75. manual pages in your programming environment). Note that there might be slight 
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  76. incompatibilities between different implementations of <span class="lang">strftime()</span>. 
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  77. </p>
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  78. <p><span class="def">string nowstring(const char* fmt, bool utc = true)</span> 
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  79. returns a string representing the current time in a format specified by <span class="lang">fmt</span>. 
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  80. <span class="lang">Utc</span> specifies whether the local time or the UTC time 
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  81. is required. Like for <span class="lang">dttostring()</span>, the syntax of the 
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  82. format specifier <span class="lang">fmt</span> is the same as for the system function 
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  83. <span class="lang">strftime()</span>.</p>
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  84. <p><span class="def">datetime utodatetime(time_t u)</span> converts UNIX <span class="lang">time_t</span> 
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  85. value to PTypes <span class="lang">datetime</span>.</p>
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  86. <p class="seealso">See also: <a href="time.calendar.html">Date/calendar manipulation</a>, 
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  87. <a href="time.time.html">Time manipulation</a></p>
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