problem with time()

Please help me understand the following:

In the following code time() funtions takes an address value, like time(&instance_of_time_t), and gives present time as output. I am wondering what is ((time_t *)0) in the_time+time((time_t *)0).

Code:

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time_t the_time;
for(i = 1; i <= 10; i++) {
the_time = time((time_t *)0);
printf("The time is &#37;ld\n", the_time);

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These two lines do the same thing

Code:

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time((time_t *)0);
time(NULL);

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The function time() returns the time value, as well as store it in the place pointed to.

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Mats

Quote:

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Originally Posted by matsp

These two lines do the same thing

Code:

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time((time_t *)0);
time(NULL);

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The function time() returns the time value, as well as store it in the place pointed to.

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Mats

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Thanks for your reply Mats. Can you please explain me what is time_t * in the fuction call time((time_t *) 0) ?

It's called a cast - which is used in C to convert different types, e.g. (double)100 is the same as 100.0, NULL is the same as (void *)0.

In C (as opposed to C++) the number 0 isn't definitely sure to be compatible with a pointer type, so it's got a cast to tell the compiler "Look, it's the number zero, but it REALLY is a time_t pointer with value zero, not an integer with value zero". It's just a homemade (and more specific) version of NULL.



--
Mats

Quote:

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Originally Posted by matsp

It's called a cast - which is used in C to convert different types, e.g. (double)100 is the same as 100.0, NULL is the same as (void *)0.

In C (as opposed to C++) the number 0 isn't definitely sure to be compatible with a pointer type, so it's got a cast to tell the compiler "Look, it's the number zero, but it REALLY is a time_t pointer with value zero, not an integer with value zero". It's just a homemade (and more specific) version of NULL.



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Mats

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This answers my query, Thank you so much!

A cast is usually made to tell the compiler that you want this conversion to be done and that you know what you're doing (which is why a cast can also be dangerous if misused).

Thanks Elysia