time函数及相关

#include <cstdlib>
#include <iostream>
#include <ctime>

using namespace std;

int main( int argc, char *argv[]);
void timestamp( void);

int main( int argc, char *argv[])
// argv : a pointer ( point to an array ( array stores pointers))
{
    int i;
    bool VERBOSE = true;
    
    if( VERBOSE)
    {
        timestamp();
        
        cout << "\n";
        cout << "ARGS\n";
        cout << " C++ version\n";
        cout <<"\n";
        cout << " Compiled on " << __DATE__ << "at" << __TIME__ << ".\n"; //显示编译时的时间
        cout << __FILE__ <<endl;
        cout << "\n";
        cout << " Print the commond line arguments of a C++ program.\n";
        cout << "\n";
        cout << " ARGC reports the number of arguments as " << argc << ".\n";
        cout << "\n";
    }

    for( i = 0; i < argc; ++i)
    {
        cout << i << " " << *argv << "\n";
        argv++;
    }

    if( VERBOSE)
    {
        cout << "\n";
        cout << "ARGS:\n";
        cout << "Normal end of execution.\n";
        cout << "\n";
        timestamp();
    }

    return 0;

}

void timestamp( void)
{
#define TIME_SIZE 40   // tips : 局部的宏定义
    static char time_buffer[TIME_SIZE];
    const struct tm *tm; // time 的结构体，包含时间的信息。
    size_t len;
    time_t now;  //就是int64变量

    now = time( NULL); // 形成时间的信息，存储在now中
    tm = localtime( &now); // 将now中的信息转换到tm中
    len = strftime( time_buffer, TIME_SIZE, "%d %B %Y %I:%M:%S %p", tm); // 将tm中的信息转到time_buffer中，
    cout << time_buffer << "\n"; // 在字符串中显示。
    return ;
# undef TIME_SIZE
}

学习到的东西：编译器预定义到的宏。http://blog.csdn.net/the__blue__sky/article/details/8921488  http://blog.csdn.net/q191201771/article/details/6092891

再次理解main函数的参数“ char *argv[]＂，argv[]是个数组，数组里面存储的是char* 指针，即数组里面的内容是指针。

// wchar.h 中
struct tm {
        int tm_sec;     /* seconds after the minute - [0,59] */
        int tm_min;     /* minutes after the hour - [0,59] */
        int tm_hour;    /* hours since midnight - [0,23] */
        int tm_mday;    /* day of the month - [1,31] */
        int tm_mon;     /* months since January - [0,11] */
        int tm_year;    /* years since 1900 */
        int tm_wday;    /* days since Sunday - [0,6] */
        int tm_yday;    /* days since January 1 - [0,365] */
        int tm_isdst;   /* daylight savings time flag */
        };

time()获得时间信息；localtime（）转换信息为时间表示的形式；strftime()将时间转换为字符串的形式，便于输出。

原型：time_t time( time_t* timer)  The value returned generally represents the number of seconds since 00:00 hours, Jan 1, 1970 UTC.  将返回的值返回到timer里面。如果timer是NULL 则返回就完了。

源代码来源：http://people.sc.fsu.edu/~jburkardt/cpp_src/args/args.cpp

ctime：http://www.cplusplus.com/reference/ctime/