time函数及相关

1 #include <cstdlib>
 2 #include <iostream>
 3 #include <ctime>
 4 
 5 using namespace std;
 6 
 7 int main( int argc, char *argv[]);
 8 void timestamp( void);
 9 
10 int main( int argc, char *argv[])
11 // argv : a pointer ( point to an array ( array stores pointers))
12 {
13     int i;
14     bool VERBOSE = true;
15     
16     if( VERBOSE)
17     {
18         timestamp();
19         
20         cout << "\n";
21         cout << "ARGS\n";
22         cout << " C++ version\n";
23         cout <<"\n";
24         cout << " Compiled on " << __DATE__ << "at" << __TIME__ << ".\n"; //显示编译时的时间
25         cout << __FILE__ <<endl;
26         cout << "\n";
27         cout << " Print the commond line arguments of a C++ program.\n";
28         cout << "\n";
29         cout << " ARGC reports the number of arguments as " << argc << ".\n";
30         cout << "\n";
31     }
32 
33     for( i = 0; i < argc; ++i)
34     {
35         cout << i << " " << *argv << "\n";
36         argv++;
37     }
38 
39     if( VERBOSE)
40     {
41         cout << "\n";
42         cout << "ARGS:\n";
43         cout << "Normal end of execution.\n";
44         cout << "\n";
45         timestamp();
46     }
47 
48     return 0;
49 
50 }
51 
52 void timestamp( void)
53 {
54 #define TIME_SIZE 40   // tips : 局部的宏定义
55     static char time_buffer[TIME_SIZE];
56     const struct tm *tm; // time 的结构体，包含时间的信息。
57     size_t len;
58     time_t now;  //就是int64变量
59 
60     now = time( NULL); // 形成时间的信息，存储在now中
61     tm = localtime( &now); // 将now中的信息转换到tm中
62     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，
63     cout << time_buffer << "\n"; // 在字符串中显示。
64     return ;
65 # undef TIME_SIZE
66 }

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/
原文链接: https://www.cnblogs.com/jiangyoumiemie/archive/2013/06/03/3116038.html

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