topic Re: MQX "struct tm" not standard C in MQX Software Solutions

MQX "struct tm" not standard C

hbouch — Wed, 19 Oct 2016 11:54:59 GMT

Hello,

When a look at the definition of the struct tm in mqx.h I see that it is a little different then standard C. Here is the definition in mqx.h:

struct tm {

/*! \brief Range from 0 to 59. */
int32_t tm_sec;

/*! \brief Range from 0 to 59. */
int32_t tm_min;

/*! \brief Range from 0 to 23. */
int32_t tm_hour;

/*! \brief Range from 0 to 30, depend on month. */
int32_t tm_mday;

/*! \brief Range from 0 to 11. */
int32_t tm_mon;

/*! \brief Range from 0, since 1900. */
int32_t tm_year;

/*! \brief Range from 0 to 6. */
int32_t tm_wday;

/*! \brief Range from 0 to 365. */
int32_t tm_yday;

    /*! \brief A flag that indicates whether daylight saving
    * time is in effect at the time described
    */
    int32_t         tm_isdst;
};

As you can see, tm_mday is ranged from 0 to 30. According to C standard, tm_mday should be ranged from 1 to 31.

Is this normal?

Re: MQX "struct tm" not standard C

danielchen — Thu, 20 Oct 2016 06:13:35 GMT

Hi Hugo:

It is normal. tm structure is a broken-down time format. you need conversion functions mktime, gmtime_r, timegm convert between this tm struct and the _time_t.

For example, in function mktime

...

/* The first day of month in DATE_STRUCT is 1, while in tm struct is 0*/
date.DAY = (int32_t)tm_ptr->tm_mday + 1;

/* The first month of year in DATE_STRUCT is 1, while in tm struct is 0*/
date.MONTH = (int32_t)tm_ptr->tm_mon + 1;

...

Regards

Daniel

Re: MQX "struct tm" not standard C

hbouch — Thu, 20 Oct 2016 08:40:47 GMT

Hi Daniel,

I know there is conversion functions to convert between broken-down time format and unix format and that's exactly the problem. I have a RTC which I have to set. I get the command and time to set from a telnet connection from a PC. When I fill the broken-down time structure, if I respect the standard C of struct tm, the date saved is not what I would expect. It is one day later. I have to substract 1 to tm_mday to be compatible with MQX struct tm.

I know it's not a big deal and I can live with that. But why didn't MQX respect the C standard ? Why is MQX implementing time.c file when it is already provided by the standard C librairies of all C compilers?

Regards,

Hugo

Re: MQX "struct tm" not standard C

adyr — Thu, 06 Apr 2017 08:22:46 GMT

I wish I had noticed this sooner.

I have been implementing a daylight saving plan in my project and have wasted a few days, thinking I had got my math wrong, only to discover this discrepancy :-(

If it is changed to be C compliant then it will break existing code that has worked around the problem so I guess it will have to stay this way.