PHP strtotime function usage, implementation principle and source code analysis, strtotime function_PHP tutorial

PHP strtotime function usage, implementation principle and source code analysis, strtotime function

Source code location: extdatephp_date.c

Copy code 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,

This also led to writing this article, which includes the following content:

1) Some uses of the .strtotime function
2) Basic principles of implementation of strtotime function
3) The reason why .strtotime(“-1 month”) failed to evaluate

Some uses 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:

Copy code 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 can also be regarded as a solution. What determines this solution? The strtotime function only calculates the month when calculating the month, which is equivalent to directly setting the month to the value of the specified month. For example, 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:

Copy code 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 designated as 1, that is, the d field in the time structure is designated as 1. The following code:

Copy 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 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 or the last one. For the date of last Sunday:

Copy code 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:

Copy code 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, and their calling format is as follows:

Copy code 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 to set 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 to set 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 outputs: 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:

Copy code 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 the input processing, the situation where both parameters exist is first identified and processed. If it is not in this state, the situation where the second parameter does not exist is processed. If neither parameter exists, an error is reported and FALSE is 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:

Copy code 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:

Copy code 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：

复制代码 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' );

In the end, relative will correspond to a series of operations. The program will recognize the -1 in the front and the month string in the back. Month corresponds to an operation type: TIMELIB_MONTH. After this, perform operations based on the identified numbers and operation types, as shown in the following code:

Copy code The code is as follows:

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

The above code directly records the relative value of the month minus one. But for situations like March 31st, where there is no 31st in February, the program will automatically calculate the date to the next month.

http://www.bkjia.com/PHPjc/953146.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/953146.htmlTechArticlePHP strtotime function usage, implementation principle and source code analysis, strtotime function source code location: extdatephp_date.c Copy the code as follows: /* {{{ proto int strtotime(string time [, i...