Why is the tm_year member in struct tm relative to 1900 rather than 1970 in C on macosx?

I was trying out the examples in expert C programming while I encountered this problem. My program basically does one thing: use the standard gmtime function and see how many years has past since 1970. Here is my program:

#include <stdio.h>
#include <time.h>

int main(int argc, char** argv) {
    time_t now = time(0);
    struct tm *t = gmtime(&now);
    printf("%d\n", t->tm_year);
    return 0;
}

The output is 117, the number of years past 1900. This is unexpected because I checked time() and man gmtime beforehand and they both said they are relative to the Epoch time (1970-1-1 00:00:00):

time() returns the time as the number of seconds since the Epoch,
1970-01-01 00:00:00 +0000 (UTC).

http://man7.org/linux/man-pages/man2/time.2.html

The ctime(), gmtime() and localtime() functions all take an argument of data type 
time_t, which represents calendar time.  When interpreted as an absolute time 
value, it represents the number of seconds elapsed since the Epoch, 1970-01-01 
00:00:00 +0000 (UTC).

http://man7.org/linux/man-pages/man3/ctime.3.html

According to the above description, my program should have returned 47 instead of 117. What is going on here?

macos sierra 10.12.5
Darwin 16.6.0 Darwin Kernel Version 16.6.0: Fri Apr 14 16:21:16 PDT 2017; root:xnu-3789.60.24~6/RELEASE_X86_64 x86_64
Apple LLVM version 8.1.0 (clang-802.0.42)