程序代码：

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

void foo( int year, int mon, int day
        , int hour, int min, int sec
        , int delta_sec )
{
    struct tm tm1 = { sec,min,hour, day,mon-1,year-1900, 0,0,0 };
    time_t t1 = mktime( &tm1 );
    if( t1 == time_t(-1) )
    {
        puts( "[ERROR] ……" );
        return;
    }

    time_t t2 = t1 + delta_sec;
    struct tm* tm2 = localtime( &t2 );
    if( !tm2 )
    {
        puts( "[ERROR] ……" );
        return;
    }

    printf( "%04d-%02d-%02d %02d:%02d:%02d\n"
        , tm2->tm_year+1900, tm2->tm_mon+1, tm2->tm_mday
        , tm2->tm_hour, tm2->tm_min, tm2->tm_sec );
}

int main( void )
{
    printf( "%s", "2015-01-01 00:00:00的后3600秒 是 " );
    foo( 2015, 1, 1, 0, 0, 0, +3600 );

    printf( "%s", "2015-01-01 00:00:00的前3600秒 是 " );
    foo( 2015, 1, 1, 0, 0, 0, -3600 );

    return 0;
}