How to convert st_mtime (which get from stat function) to string or char

Question

I need to convert st_mtime to string format for passing it to java layer, i try to use this example http://www.cplusplus.com/forum/unices/10342/ but compiler produce errors

invalid conversion from 'long unsigned int*' to 'const time_t* {aka long int const*}'

initializing argument 1 of 'tm* localtime(const time_t*)' [-fpermissive]

What i doing wrong, how to get time creation of file using stat function in string presentation.

Help please.

score 16 · Accepted Answer · answered Nov 24 '12 at 15:01

16

According to the stat(2) man page, the st_mtime field is a time_t (i.e. after reading the time(7) man page, a number of seconds since the unix Epoch).

You need localtime(3) to convert that time_t to a struct tm in local time, then, strftime(3) to convert it to a char* string.

So you could code something like:

time_t t = mystat.st_mtime;
struct tm lt;
localtime_r(&t, &lt);
char timbuf[80];
strftime(timbuf, sizeof(timbuf), "%c", &lt);

then use timbuf perhaps by strdup-ing it.

NB. I am using localtime_r because it is more thread friendly.

answered Nov 24 '12 at 15:01

Basile Starynkevitch

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If you're not fussy about the format, you can also just pass the time_t into "ctime" to get a string. (Note ctime isn't thread-safe.) – fadden Nov 27 '12 at 20:35
But the OP needs a thread-safe solution, because it is inside a JVM. – Basile Starynkevitch Nov 27 '12 at 20:42

iabdalkader · Answer 2 · 2012-11-24T15:12:12.940

9

use strftime() there's an example in the man page something like:

struct tm *tm;
char buf[200];
/* convert time_t to broken-down time representation */
tm = localtime(&t);
/* format time days.month.year hour:minute:seconds */
strftime(buf, sizeof(buf), "%d.%m.%Y %H:%M:%S", tm);
printf("%s\n", buf);

Would print the output:

"24.11.2012 17:04:33"

edited Nov 24 '12 at 15:12

answered Nov 24 '12 at 15:00

iabdalkader

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Where did you get `t`? – c0dehunter Feb 15 '16 at 08:03

score 2 · Answer 3 · edited Mar 01 '15 at 03:14

You can achieve this in an alternative way:

Declare a pointer to a tm structure:
```
struct tm *tm;
```
Declare a character array of proper size, which can contain the time string you want:
```
char file_modified_time[100];
```
Break the st.st_mtime (where st is a struct of type stat, i.e. struct stat st) into a local time using the function localtime():
```
tm = localtime(&st.st_mtim);
```
Note: st_mtime is a macro (#define st_mtime st_mtim.tv_sec) in the man page of stat(2).

Use sprintf() to get the desired time in string format or whatever the format you'd like:

sprintf(file_modified_time, "%d_%d.%d.%d_%d:%d:%d", tm->tm_year + 1900, tm->tm_mon + 1, tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec);

NB: You should use

memset(file_modified_time, '\0', strlen(file_modified_time));

before sprintf() to avoid the risk of any garbage which arises in multi-threading.

How to convert st_mtime (which get from stat function) to string or char

3 Answers3

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