BLP-chap-4 Linux环境

时间：2009-05-18 来源：mercurial-hl

程序参数

getopt用法：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main(int argc, char *argv[])
{
        int     opt;

        while ((opt=getopt(argc, argv, "if:lr")) != -1)
        {
                switch(opt) {
                case 'i':
                case 'l':
                case 'r':
                        printf("option:%c\n", opt);
                        break;
                case 'f':
                        printf("filename: %s\n", optarg);
                        break;
                case ':':
                        printf("option needs a value\n");
                        break;
                case '?':
                        printf("unknow option: %c\n", optopt);
                        break;
                }
        }

        for (; optind<argc; optind++)
        {
                printf("argument: %s \n", argv[optind]);
        }

        exit(0);
}

运行：

[root@localhost chap4]# ./argopt -i -lr 'hi here' -f fred.c -q
option:i
option:l
option:r
filename: fred.c
./argopt: invalid option -- q
unknow option: q
argument: hi here

getopt_long略

环境变量

环境变量详解：环境变量

environ：

#include <stdio.h>
#include <stdlib.h>

extern char **environ;

int
main(void)
{
        char **env = environ;

        while (*env)
        {
                printf("%s\n", *env);
                env++;
        }

        exit(0);
}

getenv与putenv：

#include <string.h>
#include <stdlib.h>
#include <stdio.h>

int
main(int argc, char *argv[])
{
        char    *var;     /* 环境变量名 */
        char    *value;   /* 环境变量值 */

        if (argc ==1 || argc > 3)
        {
                fprintf(stderr, "useage: ./environ var [value]\n");
                exit(1);
        }

        var = argv[1];
        value = getenv(var);    /* 获取环境变量的值 */
        if (value)
                printf("variable %s has value %s \n", var, value);
        else
                printf("variable %s has no value\n");

        /* 在程序中设置环境变量的值 */
        if (argc == 3)
        {
                char    *string;
                value = argv[2];
                if (!(string = malloc(strlen(var) + strlen(value) + 2)))
                {
                        fprintf(stderr, "overflow\n");
                        exit(1);
                }
                strcpy(string, var);
                strcat(string, "=");
                strcat(string, value);

                printf("calling putenv to %s \n", string);

                if (putenv(string) != 0)        /* 设置环境变量 */
                {
                        fprintf(stderr, "putenv faile\n");
                        free(string);
                        exit(1);
                }

                value = getenv(var); /* 获取新值 */
                if (value)
                        printf("new value of %s is %s\n", var, value);
                else
                        printf("new value of %s is null???\n", var);
        }

        exit(0);
}

运行：

[root@localhost chap4]# ./environ HOME
variable HOME has value /root
[root@localhost chap4]# ./environ NOSUCHENV
variable has no value
[root@localhost chap4]# ./environ NOSUCHENV hello
variable has no value
calling putenv to NOSUCHENV=hello
new value of NOSUCHENV is hello
[root@localhost chap4]# ./environ NOSUCHENV
variable has no value

时间日期

time函数：

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
        time_t the_time;
        int     i;

        for (i=0; i<5; i++)
        {
                the_time = time((time_t *)0);
                printf("The time is : %ld\n", the_time);
                sleep(3);
        }

        exit(0);
}

运行：

[root@localhost chap4]# ./envtime
The time is : 1242628048
The time is : 1242628051
The time is : 1242628054
The time is : 1242628057
The time is : 1242628060

localtime函数：

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

int
main(void)
{
        struct tm *tm_ptr;
        time_t    the_time;

        (void)time(&the_time);
        tm_ptr = localtime(&the_time);

        printf("Raw time is %ld\n", the_time);
        printf("localtime gives:\n");
        printf("date: %02d/%02d/%02d\n",
                tm_ptr->tm_year+1900, tm_ptr->tm_mon+1, tm_ptr->tm_mday);

        printf("time:%02d:%02d:%02d\n",
                tm_ptr->tm_hour, tm_ptr->tm_min, tm_ptr->tm_sec);

        exit(0);
}

运行：

[root@localhost chap4]# ./localtime; date
Raw time is 1242637706
localtime gives:
date: 2009/05/18
time:17:08:26
Mon May 18 17:08:26 HKT 2009

ctime函数:

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

int
main(void)
{
        time_t timeval;
        time(&timeval);
        printf("the date is:%s\n", ctime(&timeval));

        exit(0);
}

运行：

[root@localhost chap4]# ./ctime
the date is:Mon May 18 17:12:37 2009