PHP strtotime function usage, implementation principle and source code analysis_PHP tutorial

PHP strtotime function usage, implementation principle and source code analysis

This article mainly introduces the PHP strtotime function usage, implementation principle and source code analysis. This article explains some usages of the strtotime function. , the basic principles of the implementation of the strtotime function, the reasons for the failure of strtotime (“-1 month”) evaluation, etc. Friends who need it can refer to it

Source code location: extdatephp_date.c

The code is as follows:

　/* {{{ proto int strtotime(string time [, int now])

　Convert string representation of date and time to a timestamp */

PHP_FUNCTION(strtotime)

　{

Char *times, *initial_ts;

　int time_len, error1, error2;

struct timelib_error_container *error;

long preset_ts = 0, ts;

timelib_time *t, *now;

timelib_tzinfo *tzi;

　tzi = get_timezone_info(TSRMLS_C);

　if (zend_parse_parameters_ex(ZEND_PARSE_PARAMS_QUIET, ZEND_NUM_ARGS() TSRMLS_CC, “sl”, ×, &time_len, &preset_ts) != FAILURE) {

　/* We have an initial timestamp */

now = timelib_time_ctor();

initial_ts = emalloc(25);

snprintf(initial_ts, 24, “@%ld UTC”, preset_ts);

　t = timelib_strtotime(initial_ts, strlen(initial_ts), NULL, DATE_TIMEZONEDB, php_date_parse_tzfile_wrapper); /* we ignore the error here, as this should never fail */

timelib_update_ts(t, tzi);

now->tz_info = tzi;

now->zone_type = TIMELIB_ZONETYPE_ID;

timelib_unixtime2local(now, t->sse);

timelib_time_dtor(t);

efree(initial_ts);

　} else if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, “s|l”, ×, &time_len, &preset_ts) != FAILURE) {

　/* We have no initial timestamp */

now = timelib_time_ctor();

now->tz_info = tzi;

now->zone_type = TIMELIB_ZONETYPE_ID;

timelib_unixtime2local(now, (timelib_sll) time(NULL));

　} else {

RETURN_FALSE;

　}

　if (!time_len) {

timelib_time_dtor(now);

RETURN_FALSE;

　}

　t = timelib_strtotime(times, time_len, &error, DATE_TIMEZONEDB, php_date_parse_tzfile_wrapper);

error1 = error->error_count;

timelib_error_container_dtor(error);

timelib_fill_holes(t, now, TIMELIB_NO_CLONE);

timelib_update_ts(t, tzi);

　ts = timelib_date_to_int(t, &error2);

timelib_time_dtor(now);

timelib_time_dtor(t);

　if (error1 || error2) {

RETURN_FALSE;

　} else {

RETURN_LONG(ts);

　}

　}

　/* }}} */

The strtotime function will have some problems when using strtotime(“-1 month”) to find today’s day of the previous month,

Therefore, this article was written. This article includes the following content:

　1) Some uses of the .strtotime function

　2) Basic principles of implementation of the strtotime function

　3) The reason why .strtotime(“-1 month”) failed to evaluate

Some usages of strtotime function

　1. strtotime(“JAN”) and strtotime(“January”)

The effect of these two usages is the same. They both return today's day in the specified month. If there is no today in the specified month, it will be postponed to the next month. For example, if February is calculated on 2011-03-31, the code is:

The code is as follows:

echo date("Y-m-d H:i:s", strtotime("feb", strtotime("2011-03-31")));

The program will output: 2011-03-03 00:00:00. From the appearance point of view, this result may not necessarily be what we want, but it is also a solution. What determines this solution? The strtotime function only calculates the month when calculating the month, which is equivalent to Directly set the month to the value of the specified month, and such as jan and January will have a corresponding internal value.

2. first keyword

First is an auxiliary keyword. It can be used in combination with keywords such as week, day, etc. that can specify confirmation values. For example, to find the first Sunday in 2011:

The code is as follows:

echo date("Y-m-d H:i:s", strtotime("second sunday", strtotime("2011-01-01"))), "
";

In the PHP source code, the combined use of first, week and day is separate, that is, first day corresponds to a processing operation. In the final C implementation, the value of day is specified as 1, which is d in the time structure. The field is specified as 1, as shown in the following code:

The code is as follows:

switch (time->relative.first_last_day_of) {

case 1: /* first */

time->d = 1;

break;

case 2: /* last */

time->d = 0;

time->m++;

break;

　}

3. previous and next keywords

Similar to first, the previous keyword can be used in combination with week and day to indicate the day of the week or day before the specified time. The code is as follows:

Copy the code. The code is as follows:

echo date("Y-m-d H:i:s", strtotime("previous sunday", strtotime("2011-02-01"))), "
";

The program will output: 2011-01-30 00:00:00

The program seeks the Sunday before 2011-02-01.

The next keyword is the opposite of previous, it indicates the next day of the week or the day after.

4. last keyword

The last keyword can be used as either the previous one or the last one. For the date of last Sunday:

The code is as follows:

echo date("Y-m-d H:i:s", strtotime("last sunday", strtotime("2011-02-05"))), "
";

The program will output: 2011-01-30 00:00:00

When the program is used as the last, its application scenario is the last day of the month where the specified date is located, which is equivalent to the result of date("t"). Please find the last day of February 2000:

The code is as follows:

echo date("Y-m-d H:i:s", strtotime("last day", strtotime("2000-02-01"))), "
";

The first, previous, last and this keywords belong to the same group in the re file.

5. back and front keywords

These two keywords are forward and backward operations on the hours of the day. The calling format is as follows:

The code is as follows:

echo date("Y-m-d H:i:s", strtotime("back of 24", strtotime("2011-02-01"))), "
";

echo date("Y-m-d H:i:s", strtotime("front of 24", strtotime("2011-02-01"))), "
";

Back means setting the time to 15 minutes of the hour after the specified hour value. If it is 24:00, it will be counted to 0:15 of the next day.

Front means setting the time to 45 minutes of the hour before the specified hour value. If it is 0 o'clock, it is calculated as 23:45 of the previous day.

The above code output: 2011-02-02 00:15:00 2011-02-01 23:45:00. The arrays followed by back of and front of must be greater than or equal to 0 and less than or equal to 24.

Basic principles of implementation of strtotime function

The official document describes the strtotime function as follows: This function is expected to accept a string containing a US English date format and try to parse it into a Unix timestamp (seconds since January 1 1970 00:00:00 GMT number), its value is relative to the time given by the now parameter. If this parameter is not provided, the current system time is used.

This is a standard PHP built-in function that has existed since PHP4. The strtotime function is loaded as an extension, and its full implementation is available in the ext/date directory. As a standard built-in function, its definition format is also standard, as follows:

The code is as follows:

PHP_FUNCTION(strtotime)

// Process input, whether there is a second parameter or not

// Call related functions to implement string parsing and result calculation

// Return results

　}

In input processing, first identify the situation where both parameters exist and process it. If it is not in this state, process the situation where the second parameter does not exist. If neither parameter exists, an error will be reported and FALSE will be returned.

The first parameter of the strtotime function is a string. For this string, due to its complexity, PHP uses the same tool as its lexical parsing: re2c. In the /ext/date/lib directory, we can see its original re file from the parse_date.re file. When the user passes in a string in the form of a parameter, the string will be handed over to this program for processing, and different processing functions will be matched according to the different strings. For example, if strtotime("yesterday") is called, when analyzing the string, it will match the yesterday string. The corresponding function of this string is as follows:

The code is as follows:

'yesterday'

　{

DEBUG_OUTPUT("yesterday");

TIMELIB_INIT;

　TIMELIB_HAVE_RELATIVE();

　TIMELIB_UNHAVE_TIME();

s->time->relative.d = -1;

TIMELIB_DEINIT;

return TIMELIB_RELATIVE;

　}

Here are several key structures:

The code is as follows:

typedef struct Scanner {

int fd;

uchar *lim, *str, *ptr, *cur, *tok, *pos;

unsigned int line, len;

struct timelib_error_container *errors;

struct timelib_time *time;

const timelib_tzdb *tzdb;

　} Scanner;

typedef struct timelib_time {

timelib_sll y, m, d; /* Year, Month, Day */

timelib_sll h, i, s; /* Hour, mInute, Second */

double f; /* Fraction */

　int z; /* GMT offset in minutes */

　　char *tz_abbr; /* Timezone abbreviation (display only) */

　　timelib_tzinfo *tz_info; /* Timezone structure */

　　signed int dst; /* Flag if we were parsing a DST zone */

　　timelib_rel_time relative;

　　timelib_sll sse; /* Seconds since epoch */

　　unsigned int have_time, have_date, have_zone, have_relative, have_weeknr_day;

　　unsigned int sse_uptodate; /* !0 if the sse member is up to date with the date/time members */

　　unsigned int tim_uptodate; /* !0 if the date/time members are up to date with the sse member */

　　unsigned int is_localtime; /* 1 if the current struct represents localtime, 0 if it is in GMT */

　　unsigned int zone_type; /* 1 time offset,

　　* 3 TimeZone identifier,

　　* 2 TimeZone abbreviation */

　　} timelib_time;

　　typedef struct timelib_rel_time {

　　timelib_sll y, m, d; /* Years, Months and Days */

　　timelib_sll h, i, s; /* Hours, mInutes and Seconds */

　　int weekday; /* Stores the day in 'next monday' */

　　int weekday_behavior; /* 0: the current day should *not* be counted when advancing forwards; 1: the current day *should* be counted */

　　int first_last_day_of;

　　int invert; /* Whether the difference should be inverted */

　　timelib_sll days; /* Contains the number of *days*, instead of Y-M-D differences */

　　timelib_special special;

　　unsigned int have_weekday_relative, have_special_relative;

　　} timelib_rel_time;

　　s->time->relative.d = -1;所表示的意思是当前时间的相对天数是-1。 这只是中间词法解析的中间结果，但是最后结果是通过这些中间结果计算出来的。

　　strtotime(“-1 month”)求值失败的原因

　　虽然strtotime(“-1 month”)这种方法对于后一个月比前一个月的天数的情况会求值失败，但是从其本质上来说，这并没有错。 PHP这样实现也无可厚非。只是我们的需求决定了我们不能使用这种方法，因此我们称其为求值失败。

　　我们来看它的实现过程，由于没有第二个参数，所以程序使用默认的当前时间。 第一个参数传入的是-1 month字符串，这个字符串所对应的re文件中的正则为：

　　代码如下:

　　reltextunit = (('sec'|'second'|'min'|'minute'|'hour'|'day'|'fortnight'|'forthnight'|'month'|'year') 's'?) | 'weeks' | daytext;

　　relnumber = ([+-]*[ t]*[0-9]+);

　　relative = relnumber space? (reltextunit | 'week' );

　　最终relative会对应一系列操作，程序会识别出前面的-1 和后面的month字符串，month对应一种操作类型：TIMELIB_MONTH。 在此之后，根据识别出来的数字和操作类型执行操作，如下代码：

　　代码如下:

　　case TIMELIB_MONTH: s->time->relative.m += amount * relunit->multiplier; break;

 

　　如上代码，则是直接记录月份的相对值减一。 但是对于类似于3月31号这样的情况，2月没有31号，程序会自动将日期计算到下一个月。

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