CODEWITHSUNDEEP
cpointerstime.hdangling-pointer
William Rantis
William Rantis

Reputation: 1

C gmtime() Variable scope

I have been working with C and I thought that a pointer should not point to a local variable, but the library holds a function gmtime(), which seems to return a pointer to a variable created inside of it. Is my understanding correct?

time_t epochTime;
time(&epochTime);
struct tm *currentTime=gmtime(&epochTime);

Upvotes: 0

Views: 182

Answers (2)

rtx13
rtx13

Reputation: 2610

It's not returning a pointer to a local variable, rather it is returning a pointer to a statically allocated memory region.

From man page:

The return value points to a statically allocated struct which might be overwritten by subsequent calls to any of the date and time functions.

A statically allocated memory region could simply be a global variable, or a static local variable. The latter does not exist on the stack, but rather in the data segment along with other statically-allocated data member.

Upvotes: 0

dbush
dbush

Reputation: 224387

Internally, gmtime contains a variable declared with the static storage class specifier. That means that the variable has full program lifetime and therefore it is valid to return its address from the function.

This also means that if you save that pointer somewhere and call gmtime again with a different parameter, it changes what the saved pointer points to.

Upvotes: 1

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