Question

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What primitive data type is time_t?

Basically, all I want to do is produce the current UNIX time (result from time(NULL)) and print it to a file I have open.

I’ve tried code such as:

fprintf(f, "%i", time(NULL));

But I get these annoying compiler warnings:

src/database-createtbl.c:140: warning: int format, time_t arg (arg 3)

I’m trying to compile using -Wall – this really shouldn’t be an issue but it’s driving me nuts.

Answer 1

Simply cast to a known type:

printf("%ld", (long)time(NULL));

The type returned by time depends on the OS (it’s aliased to time_t, but you don’t know if this is long or int or something else), so you need to cast it to a known type before passing it to printf, in order for the format to match the argument type.