time function in c keeps returning -1

Question

Hi I hava a little problem because the function time() keeps returning -1 is there any posible way to fix this?

I tried:

time_t start, end; start = time(NULL); //do something end = time(NULL);

But when I debug both have the value -1. and I tried:

time_t start, end; time(&start); // do something time(&end);

But in this case both values stay 0.

I use them in if (difftime(mod_end, mod_start) < TCK_WAIT_TIME_SEC) but I check the values in the debuger — holysloth
– holysloth, Commented Nov 12, 2015 at 13:09
What does it print if you do this: start = time(NULL); if (start==(time_t)-1) perror("time failed"); else printf("start=%ld\n",start); — dbush
– dbush, Commented Nov 12, 2015 at 13:16
have you tried a minimal working example of this? and just print out the content of your start-value? — Tom Mekken
– Tom Mekken, Commented Nov 12, 2015 at 13:16
What C compiler? The function works as expected in gcc 4.9 (with both ways of calling it). — Mr Lister
– Mr Lister, Commented Nov 12, 2015 at 13:18

paxdiablo · Accepted Answer · 2015-11-19 11:14:39Z

It's perfectly valid, according to ISO C, for time() to return -1 if it cannot establish the time. From ISO C11 7.27.2.4 The time function /3 (though this behaviour has been around for a long time):

The time function returns the implementation’s best approximation to the current calendar time. The value (time_t)(-1) is returned if the calendar time is not available.

Given that you're working with Simplicity Studio, a package frequently used for embedded systems, it's possible your target environment may not be able to establish the calendar time (if, for example, it does not have a real-time clock to query).

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