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tzset.3p (3886B)

    

  1. '\" et
  2. .TH TZSET "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
  3. .\"
  4. .SH PROLOG
  5. This manual page is part of the POSIX Programmer's Manual.
  6. The Linux implementation of this interface may differ (consult
  7. the corresponding Linux manual page for details of Linux behavior),
  8. or the interface may not be implemented on Linux.
  9. .\"
  10. .SH NAME
  11. daylight,
  12. timezone,
  13. tzname,
  14. tzset
  15. \(em set timezone conversion information
  16. .SH SYNOPSIS
  17. .LP
  18. .nf
  19. #include <time.h>
  20. .P
  21. extern int daylight;
  22. extern long timezone;
  23. extern char *tzname[2];
  24. void tzset(void);
  25. .fi
  26. .SH DESCRIPTION
  27. The
  28. \fItzset\fR()
  29. function shall use the value of the environment variable
  30. .IR TZ
  31. to set time conversion information used by
  32. .IR "\fIctime\fR\^(\|)",
  33. .IR "\fIlocaltime\fR\^(\|)",
  34. .IR "\fImktime\fR\^(\|)",
  35. and
  36. .IR "\fIstrftime\fR\^(\|)".
  37. If
  38. .IR TZ
  39. is absent from the environment, implementation-defined default
  40. timezone information shall be used.
  41. .P
  42. The
  43. \fItzset\fR()
  44. function shall set the external variable
  45. .IR tzname
  46. as follows:
  47. .sp
  48. .RS 4
  49. .nf
  51. tzname[0] = "\fIstd\fP";
  52. tzname[1] = "\fIdst\fP";
  53. .fi
  54. .P
  55. .RE
  56. .P
  57. where
  58. .IR std
  59. and
  60. .IR dst
  61. are as described in the Base Definitions volume of POSIX.1\(hy2017,
  62. .IR "Chapter 8" ", " "Environment Variables".
  63. .P
  64. The
  65. \fItzset\fR()
  66. function also shall set the external variable
  67. .IR daylight
  68. to 0 if Daylight Savings Time conversions should never be applied for
  69. the timezone in use; otherwise, non-zero. The external variable
  70. .IR timezone
  71. shall be set to the difference, in seconds, between Coordinated
  72. Universal Time (UTC) and local standard time.
  73. .P
  74. If a thread accesses
  75. .IR tzname ,
  76. .IR daylight ,
  77. or
  78. .IR timezone
  79. directly while another thread is in a call to
  80. \fItzset\fR(),
  81. or to any function that is required or allowed to set timezone
  82. information as if by calling
  83. \fItzset\fR(),
  84. the behavior is undefined.
  85. .SH "RETURN VALUE"
  86. The
  87. \fItzset\fR()
  88. function shall not return a value.
  89. .SH ERRORS
  90. No errors are defined.
  91. .LP
  92. .IR "The following sections are informative."
  93. .SH EXAMPLES
  94. Example
  95. .IR TZ
  96. variables and their timezone differences are given in the table below:
  97. .TS
  98. center box tab(!);
  99. cI | cI
  100. lw(1i) | lw(1i).
  101. TZ!timezone
  102. _
  103. EST5EDT!5*60*60
  104. GMT0!0*60*60
  105. JST-9!\-9*60*60
  106. MET-1MEST!\-1*60*60
  107. MST7MDT!7*60*60
  108. PST8PDT!8*60*60
  109. .TE
  110. .SH "APPLICATION USAGE"
  111. Since the
  112. \fIctime\fR(),
  113. \fIlocaltime\fR(),
  114. \fImktime\fR(),
  115. \fIstrftime\fR(),
  116. and
  117. \fIstrftime_l\fR()
  118. functions are required to set timezone information as if by calling
  119. \fItzset\fR(),
  120. there is no need for an explicit
  121. \fItzset\fR()
  122. call before using these functions. However, portable applications
  123. should call
  124. \fItzset\fR()
  125. explicitly before using
  126. \fIctime_r\fR()
  127. or
  128. \fIlocaltime_r\fR()
  129. because setting timezone information is optional for those functions.
  130. .SH RATIONALE
  131. None.
  132. .SH "FUTURE DIRECTIONS"
  133. None.
  134. .SH "SEE ALSO"
  135. .IR "\fIctime\fR\^(\|)",
  136. .IR "\fIlocaltime\fR\^(\|)",
  137. .IR "\fImktime\fR\^(\|)",
  138. .IR "\fIstrftime\fR\^(\|)"
  139. .P
  140. The Base Definitions volume of POSIX.1\(hy2017,
  141. .IR "Chapter 8" ", " "Environment Variables",
  142. .IR "\fB<time.h>\fP"
  143. .\"
  144. .SH COPYRIGHT
  145. Portions of this text are reprinted and reproduced in electronic form
  146. from IEEE Std 1003.1-2017, Standard for Information Technology
  147. -- Portable Operating System Interface (POSIX), The Open Group Base
  148. Specifications Issue 7, 2018 Edition,
  149. Copyright (C) 2018 by the Institute of
  150. Electrical and Electronics Engineers, Inc and The Open Group.
  151. In the event of any discrepancy between this version and the original IEEE and
  152. The Open Group Standard, the original IEEE and The Open Group Standard
  153. is the referee document. The original Standard can be obtained online at
  154. http://www.opengroup.org/unix/online.html .
  155. .PP
  156. Any typographical or formatting errors that appear
  157. in this page are most likely
  158. to have been introduced during the conversion of the source files to
  159. man page format. To report such errors, see
  160. https://www.kernel.org/doc/man-pages/reporting_bugs.html .