背景

在設備應用中，用戶需要根據自己的時區設置設備時區。在可交互的系統中或者完整的linux系統中可以通過設置/etc/TZ等時區文件鏈接的文件來修改設備時區。但是在一些rtos或者不能使用上面設置TZ文件方式的系統中，可以通過設置應用進程的TZ環境變量的方式來設置時區，此時在通過localtime等函數轉換的時間就是本地時間了。

效果展示

$ make test ./timezone Europe/London ts 1647169200, date 2022-03-13 11:00:00 America/Anchorage ts 1647169199, date 2022-03-13 01:59:59 America/Anchorage ts 1647169200, date 2022-03-13 03:00:00 Australia/Adelaide ts 1647169200, date 2022-03-13 21:30:00Europe/London ts 1648917000, date 2022-04-02 17:30:00 America/Anchorage ts 1648917000, date 2022-04-02 08:30:00 Australia/Adelaide ts 1648916999, date 2022-04-03 02:59:59 Australia/Adelaide ts 1648917000, date 2022-04-03 02:00:00

代碼展示

citylist.h

#ifndef __CITYLIST_H_ #define __CITYLIST_H_static const char cityList[][2][128]={{ "Pacific/Midway", "SST11" },{ "Pacific/Honolulu", "HST10" },{ "America/Anchorage", "AKST9AKDT,M3.2.0,M11.1.0" },{ "America/Los_Angeles", "PST8PDT,M3.2.0,M11.1.0" },{ "America/Tijuana", "PST8PDT,M3.2.0,M11.1.0" },{ "America/Phoenix", "MST7" },{ "America/Chihuahua", "MST7MDT,M4.1.0,M10.5.0" },{ "America/Denver", "MST7MDT,M3.2.0,M11.1.0" },{ "America/Costa_Rica", "CST6" },{ "America/Chicago", "CST6CDT,M3.2.0,M11.1.0" },{ "America/Mexico_City", "CST6CDT,M4.1.0,M10.5.0" },{ "America/Regina", "CST6" },{ "America/Bogota", "<-05>5" },{ "America/New_York", "EST5EDT,M3.2.0,M11.1.0" },{ "America/Caracas", "<-04>4" },{ "America/Barbados", "AST4" },{ "America/Halifax", "AST4ADT,M3.2.0,M11.1.0" },{ "America/Manaus", "<-04>4" },{ "America/Santiago", "" },{ "America/St_Johns", "NST3:30NDT,M3.2.0,M11.1.0" },{ "America/Sao_Paulo", "<-03>3" },{ "America/Argentina/Buenos_Aires", "<-03>3" },{ "America/Godthab", "" },{ "America/Montevideo", "<-03>3" },{ "Atlantic/South_Georgia", "<-02>2" },{ "Atlantic/Azores", "<-01>1<+00>,M3.5.0/0,M10.5.0/1" },{ "Atlantic/Cape_Verde", "<-01>1" },{ "Africa/Casablanca", "<+01>-1" },{ "Europe/London", "GMT0BST,M3.5.0/1,M10.5.0" },{ "Europe/Amsterdam", "CET-1CEST,M3.5.0,M10.5.0/3" },{ "Europe/Belgrade", "CET-1CEST,M3.5.0,M10.5.0/3" },{ "Europe/Brussels", "CET-1CEST,M3.5.0,M10.5.0/3" },{ "Europe/Sarajevo", "CET-1CEST,M3.5.0,M10.5.0/3" },{ "Africa/Windhoek", "CAT-2" },{ "Africa/Brazzaville", "WAT-1" },{ "Asia/Amman", "EET-2EEST,M3.5.4/24,M10.5.5/1" },{ "Europe/Athens", "EET-2EEST,M3.5.0/3,M10.5.0/4" },{ "Europe/Istanbul", "<+03>-3" },{ "Asia/Beirut", "EET-2EEST,M3.5.0/0,M10.5.0/0" },{ "Africa/Cairo", "EET-2" },{ "Europe/Helsinki", "EET-2EEST,M3.5.0/3,M10.5.0/4" },{ "Asia/Jerusalem", "" },{ "Europe/Minsk", "<+03>-3" },{ "Africa/Harare", "CAT-2" },{ "Asia/Baghdad", "<+03>-3" },{ "Europe/Moscow", "MSK-3" },{ "Asia/Kuwait", "<+03>-3" },{ "Africa/Nairobi", "EAT-3" },{ "Asia/Tehran", "<+0330>-3:30<+0430>,J79/24,J263/24" },{ "Asia/Baku", "<+04>-4" },{ "Asia/Tbilisi", "<+04>-4" },{ "Asia/Yerevan", "<+04>-4" },{ "Asia/Dubai", "<+04>-4" },{ "Asia/Kabul", "<+0430>-4:30" },{ "Asia/Karachi", "PKT-5" },{ "Asia/Oral", "<+05>-5" },{ "Asia/Yekaterinburg", "<+05>-5" },{ "Asia/Calcutta", "IST-5:30" },{ "Asia/Colombo", "<+0530>-5:30" },{ "Asia/Katmandu", "<+0545>-5:45" },{ "Asia/Almaty", "<+06>-6" },{ "Asia/Rangoon", "<+0630>-6:30" },{ "Asia/Krasnoyarsk", "<+07>-7" },{ "Asia/Bangkok", "<+07>-7" },{ "Asia/Jakarta", "WIB-7" },{ "Asia/Shanghai", "CST-8" },{ "Asia/Hong_Kong", "HKT-8" },{ "Asia/Irkutsk", "<+08>-8" },{ "Asia/Kuala_Lumpur", "<+08>-8" },{ "Australia/Perth", "AWST-8" },{ "Asia/Taipei", "CST-8" },{ "Asia/Seoul", "KST-9" },{ "Asia/Tokyo", "JST-9" },{ "Asia/Yakutsk", "<+09>-9" },{ "Australia/Adelaide", "ACST-9:30ACDT,M10.1.0,M4.1.0/3" },{ "Australia/Darwin", "ACST-9:30" },{ "Australia/Brisbane", "AEST-10" },{ "Australia/Hobart", "AEST-10AEDT,M10.1.0,M4.1.0/3" },{ "Australia/Sydney", "AEST-10AEDT,M10.1.0,M4.1.0/3" },{ "Asia/Vladivostok", "<+10>-10" },{ "Pacific/Guam", "ChST-10" },{ "Asia/Magadan", "<+11>-11" },{ "Pacific/Majuro", "<+12>-12" },{ "Pacific/Auckland", "NZST-12NZDT,M9.5.0,M4.1.0/3" },{ "Pacific/Fiji", "" },{ "Pacific/Tongatapu", "<+13>-13" } };#endif

main.c

#include <stdio.h> #include <string.h> #include <time.h> #include <stdlib.h>#include "citylist.h"/*** @brief 根據設置的地區設置時區* */ int setTimeZone( const char *pRegion ) {int ret = 0;for( int i=0; i<sizeof(cityList)/2/128; i++ ){/* printf("--->%s,%d,%s\n", pRegion, i, cityList[i][0]); */if( strcmp( pRegion, cityList[i][0] ) == 0 ){setenv( "TZ", cityList[i][1], 1 );break;}}tzset();return ret; }void printTime( const char *pRegion, time_t ts ) {setTimeZone(pRegion);struct tm *date = localtime( &ts );printf("%-20s ts %lu, date %4d-%02d-%02d %02d:%02d:%02d\n", pRegion, ts, date->tm_year+1900, date->tm_mon+1, date->tm_mday, date->tm_hour, date->tm_min, date->tm_sec); }int main() {time_t ts;ts = 1647169200;printTime( "Europe/London", ts );printTime( "America/Anchorage", ts-1 );printTime( "America/Anchorage", ts );printTime( "Australia/Adelaide", ts );printf("\n\n");ts = 1648917000;printTime( "Europe/London", ts );printTime( "America/Anchorage", ts );printTime( "Australia/Adelaide", ts-1 );printTime( "Australia/Adelaide", ts );return 0; }

Makefile

taget=timezoneall: $(taget)$(taget): main.cgcc -o $@ $^test: $(taget)./$(taget)clean:rm $(taget)

拓展

其中citylist.h中的城市列表中的環境變量是從linux的時區文件中提取的。
提取環境變量的代碼為：
tzif-display.c

#define _GNU_SOURCE #define _POSIX_C_SOURCE #include <stdio.h> /// For printf, fopen, fclose, FILE #include <stdlib.h> /// For malloc, free #include <error.h> /// For error #include <errno.h> /// For errno #include <string.h> /// for memset, memcpy, memmem #include <sys/stat.h> /// for stat #include <locale.h> /// for setlocale #include <time.h> /// for ctime_r, tzset#define TRUE -1 #define FALSE 0/*************************************************** * definition of a tzfile header ***************************************************/ #define HEADER_LEN 44 typedef struct {char magicnumber[6]; // = TZif2 or TZif\0 // char reserved[15]; // nullslong unsigned ttisgmtcnt; // number of UTC/local indicators stored in the file.long unsigned ttisstdcnt; // number of standard/wall indicators stored in the file.long unsigned leapcnt; // number of leap seconds for which data is stored in the file.long unsigned timecnt; // number of "transition times" for which data is stored in the file.long unsigned typecnt; // number of "local time types" for which data is stored in the file (must not be zero).long unsigned charcnt; // number of characters of "timezone abbreviation strings" stored in the file.} timezonefileheader; #define TZIF1_FIELD_SIZE 4 #define TZIF2_FIELD_SIZE 8/*************************************************** * parse a tzfile "long format" value ***************************************************/ long parse_tz_long( const char *sourceptr, const int field_size) {long retval = 0;char *long_ptr;// if (sizeof(long) < field_size) // printf("warning: field truncated because it is larger than a 'long' integer\n\n");int i,j;long_ptr = (char*) &retval;if ((field_size < sizeof(long)) && (sourceptr[0] >> 8)){for (i=sizeof(long)-1; (i>=field_size); i--) long_ptr[i] = 255; }j = 0;for (i=field_size-1; (i>=0) && (j<sizeof(long)); i--){long_ptr[j] = sourceptr[i];j++;}return retval; }/*************************************************** * read a tzheader file ***************************************************/ int read_tz_header( timezonefileheader *header, const char *temp_buffer) {const int field_size = 4;memcpy( header->magicnumber, &temp_buffer[0], 5 );header->magicnumber[5] = '\0';header->ttisgmtcnt = parse_tz_long(&temp_buffer[20], field_size);header->ttisstdcnt = parse_tz_long(&temp_buffer[24], field_size);header->leapcnt = parse_tz_long(&temp_buffer[28], field_size);header->timecnt = parse_tz_long(&temp_buffer[32], field_size);header->typecnt = parse_tz_long(&temp_buffer[36], field_size);header->charcnt = parse_tz_long(&temp_buffer[40], field_size);if (header->typecnt == 0){printf("Error in file format. Zero local time types suggested.\n");return FALSE;}if (header->timecnt == 0){printf("No transition times recorded in this file\n");return FALSE;}return TRUE; }/*********************************************************************** * tzif2_handle ***********************************************************************/ char* tzif2_handle( timezonefileheader *tzh, const char *tzfile_buffer_ptr, size_t buffer_size ) {char *start_ptr;char magicnumber[5] = "TZif2";start_ptr = memmem( tzfile_buffer_ptr, buffer_size, &magicnumber, 5 );if (start_ptr == NULL){printf("error finding tzif2 header\n");return NULL;}if ( read_tz_header( tzh, (char*) start_ptr ) == FALSE ){printf("Error reading header file version 2\n");return NULL;}return start_ptr + HEADER_LEN; }/*************************************************** * Display contents of a timezone file ***************************************************/ void handle_tzfile_data( char *tz,const timezonefileheader tzh,const char* tzfile_buffer_ptr,const int field_size /// 4bytes for tzif1, 8bytes for tzif2) {/**************************************************** * Structure of the timezone files* ***************************************************/char *local_time_type_ptr;char *ttinfo_read_ptr;char* tz_abbrev_ptr;char *leapinfo_ptr;char *wall_indicator_ptr;char *local_indicator_ptr;/********************************************************************* * Beginning of code for function display_tzfile_data* ********************************************************************/local_time_type_ptr = (char*) tzfile_buffer_ptr + tzh.timecnt*field_size;ttinfo_read_ptr = local_time_type_ptr + tzh.timecnt;tz_abbrev_ptr = ttinfo_read_ptr + (tzh.typecnt * 6);leapinfo_ptr = tz_abbrev_ptr + (tzh.charcnt);wall_indicator_ptr = leapinfo_ptr + (tzh.leapcnt*field_size*2);local_indicator_ptr = wall_indicator_ptr + tzh.ttisstdcnt;if (field_size == TZIF2_FIELD_SIZE){char *start_line_ptr;start_line_ptr = strchr( local_indicator_ptr + tzh.ttisgmtcnt, 10 );if (start_line_ptr == NULL)printf("\nno \'general rule\' information found at end of file\n");else{char *end_line_ptr;end_line_ptr = strchr( start_line_ptr+1, 10 );if (end_line_ptr == NULL)printf("\nerror finding \'general rule\' info terminator symbol\n");else{*end_line_ptr = '\0';/* printf("\ngeneral rule (unparsed): %s\n", start_line_ptr+1 ); */memcpy( tz, start_line_ptr+1, end_line_ptr - start_line_ptr );}}}}#define TZ_DIR_LIST "/usr/share/zoneinfo" int GetTZValFromZoneinfo(const char *zoneInfo, char *TZ ) {int ret = 0;FILE *tz_file;char *tzif_buffer_ptr;char *start_ptr;int field_size;struct stat file_status;timezonefileheader tzh;do{char zoneInfoPath[128];snprintf( zoneInfoPath, sizeof(zoneInfoPath),"%s/%s", TZ_DIR_LIST, zoneInfo );tz_file = fopen( zoneInfoPath, "rb");if (tz_file == NULL){error(errno,0,"tz file %s not found\n", zoneInfoPath);ret = -1;break;}if (fstat( fileno( tz_file), &file_status) != 0){printf("error retreiving file status\n");ret = -1;break;}tzif_buffer_ptr = (char *) malloc( file_status.st_size );if (tzif_buffer_ptr == NULL){printf("memory allocation error - tzif buffer\n");ret = errno;break;}if ( fread( tzif_buffer_ptr, file_status.st_size, 1, tz_file) != 1 ){printf("error reading into tzif buffer\n");free(tzif_buffer_ptr);ret = errno;break;}fclose(tz_file);if ( read_tz_header( &tzh, tzif_buffer_ptr ) == FALSE ){printf("Error reading header file version 1\n");ret = -1;break;}if (tzh.magicnumber[4] == 50 ){start_ptr = tzif2_handle( &tzh, &tzif_buffer_ptr[HEADER_LEN], file_status.st_size - HEADER_LEN);field_size = TZIF2_FIELD_SIZE;}else{start_ptr = &tzif_buffer_ptr[HEADER_LEN];field_size = TZIF1_FIELD_SIZE;}if (start_ptr != NULL ) handle_tzfile_data( TZ, tzh, start_ptr, field_size );free(tzif_buffer_ptr);}while(0);return ret; }void main( int argc, const char *argv[] ) {char tz[128];/* GetTZValFromZoneinfo( "America/New_York", tz ); */memset( tz, 0, sizeof(tz) );GetTZValFromZoneinfo( argv[1], tz );printf("tz = %s\n", tz ); }

編譯執行：

$ gcc tzif-display.c $ ./a.out Cuba tz = CST5CDT,M3.2.0/0,M11.1.0/1

如上就可以提取Cuba的環境變量為CST5CDT,M3.2.0/0,M11.1.0/1，根據需要提取對應的城市地區的環境變量

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