How do I get the unix timestamp in C as an int?

Question

I would like to get the current timestamp and print it out using fprintf.

Answer 1

For 32-bit systems:

fprintf(stdout, "%u\n", (unsigned)time(NULL));  

For 64-bit systems:

fprintf(stdout, "%lu\n", (unsigned long)time(NULL));  

Answer 2

Is just casting the value returned by time()

#include <stdio.h> #include <time.h>  int main(void) {     printf("Timestamp: %d\n",(int)time(NULL));     return 0; } 

what you want?

$ gcc -Wall -Wextra -pedantic -std=c99 tstamp.c && ./a.out Timestamp: 1343846167 

To get microseconds since the epoch, from C11 on, the portable way is to use

int timespec_get(struct timespec *ts, int base) 

Unfortunately, C11 is not yet available everywhere, so as of now, the closest to portable is using one of the POSIX functions clock_gettime or gettimeofday (marked obsolete in POSIX.1-2008, which recommends clock_gettime).

The code for both functions is nearly identical:

#include <stdio.h> #include <time.h> #include <stdint.h> #include <inttypes.h>  int main(void) {      struct timespec tms;      /* The C11 way */     /* if (! timespec_get(&tms, TIME_UTC)) { */      /* POSIX.1-2008 way */     if (clock_gettime(CLOCK_REALTIME,&tms)) {         return -1;     }     /* seconds, multiplied with 1 million */     int64_t micros = tms.tv_sec * 1000000;     /* Add full microseconds */     micros += tms.tv_nsec/1000;     /* round up if necessary */     if (tms.tv_nsec % 1000 >= 500) {         ++micros;     }     printf("Microseconds: %"PRId64"\n",micros);     return 0; }