网站 推广商系统 设计,南阳网站建站公司,电商怎么做运营,网站推广品牌建设C语言之简单的获取命令行参数和环境变量 本人的开发环境为WIN10操作系统用VMWARE虚拟的UBUNTU LINUX 18.04LTS#xff01;#xff01;#xff01; 所有代码的编辑、编译、运行都在虚拟机上操作#xff0c;初学的朋友要注意这一点#xff01;#xff01;#xff01; 详细…C语言之简单的获取命令行参数和环境变量 本人的开发环境为WIN10操作系统用VMWARE虚拟的UBUNTU LINUX 18.04LTS 所有代码的编辑、编译、运行都在虚拟机上操作初学的朋友要注意这一点 详细情况如下 songvmubuntu:~/works/xdn/boo$ uname -a
Linux ubuntu 5.4.0-150-generic #167~18.04.1-Ubuntu SMP Wed May 24 00:51:42 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux命令行参数
常见C语言main函数带有两个参数整型的argc和字符串指针型的argv。这两个参数就是命令行参数相关的参数整型 argc 保存命令行参数的数量字符串指针 argv 保存命令行参数的值命令行参数要用空格隔开测试代码如下
/* filename: opt.c */
#include stdio.h/**/
int
main (int argc, char *argv[])
{printf (Argument count : %d\n, argc);printf (Command is [%s]\n, argv[0]);return 0;
}编译运行输出结果如下
songvmubuntu:~/works/xdn/boo$ gcc opt.c -o opt
songvmubuntu:~/works/xdn/boo$ ./opt
Argument count : 1
Command is [./opt]
songvmubuntu:~/works/xdn/boo$ 带参数测试
上面的结果可见参数总量为1字符串数组引用索引为0即argv[0]也就是命令本身加上两个参数测试代码如下
/* filename: opt.c */
#include stdio.h/**/
int
main (int argc, char *argv[])
{printf (Argument count : %d\n, argc);printf (Command is [%s]\n, argv[0]);for (int i 0; i argc; i)printf (Argument %d is [%s]\n, i, argv[i]);return 0;
}编译运行输出结果如下
songvmubuntu:~/works/xdn/boo$ ./opt -s zoo.t
Argument count : 3
Command is [./opt]
Argument 0 is [./opt]
Argument 1 is [-s]
Argument 2 is [zoo.t]
songvmubuntu:~/works/xdn/boo$ 提示加命令行参数
事实上你可以加任意命令行参数然后通过循环输出如果没有参数需要要提示用加上参数测试代码如下
/* filename: opt.c */
#include stdio.h/**/
int
main (int argc, char *argv[])
{printf (Argument count : %d\n, argc);printf (Command is [%s]\n, argv[0]);for (int i 0; i argc; i)printf (Argument %d is [%s]\n, i, argv[i]);if (argc 1)printf (Please add some arguments!\n);return 0;
}编译运行输出提示信息
songvmubuntu:~/works/xdn/boo$ gcc opt.c -o opt
songvmubuntu:~/works/xdn/boo$ ./opt
Argument count : 1
Command is [./opt]
Argument 0 is [./opt]
Please add some arguments!
songvmubuntu:~/works/xdn/boo$ 事实上main函数还有第三个参数envp
字符串指针envp保存系统的环境变量先读出一个环境变量看看什么情况代码如下
/* filename: opt.c */
#include stdio.h/**/
int
main (int argc, char *argv[], char *envp[])
{printf (Environment Variables\n);printf (%s\n, envp[0]);return 0;
}编译运行输出如下
songvmubuntu:~/works/xdn/boo$ gcc opt.c -o opt
songvmubuntu:~/works/xdn/boo$ ./opt
Environment Variables
CLUTTER_IM_MODULExim
songvmubuntu:~/works/xdn/boo$ 输出所有环境变量
不同编译运行环境可能输出的结果不同显示的是CLUTTER_IM_MODULExim环境变量名CLUTTER_IM_MODULE输入法模块IM - input method环境变量值xim Linux下的输入法工具包含拼音和五笔等可能是安装系统时最后安装设置的输入法所以首先显示的是这一个环境变量试一试输出所有环境变量代码如下
/* filename: opt.c */
#include stdio.h/**/
int
main (int argc, char *argv[], char *envp[])
{printf (Environment Variables\n);printf (%s\n, envp[0]);int i 0;while (envp[i] ! NULL){printf (%s\n, envp[i]);i;}return 0;
}编译运行输出如下
songvmubuntu:~/works/xdn/boo$ gcc opt.c -o opt
songvmubuntu:~/works/xdn/boo$ ./opt
Environment Variables
CLUTTER_IM_MODULExim
CLUTTER_IM_MODULExim
LS_COLORS
LC_MEASUREMENTzh_CN.UTF-8
LESSCLOSE/usr/bin/lesspipe %s %s
LC_PAPERzh_CN.UTF-8
LC_MONETARYzh_CN.UTF-8
XDG_MENU_PREFIXgnome-
LANGzh_CN.UTF-8
DISPLAY:0
OLDPWD/home/songvm/works/xdn
GNOME_SHELL_SESSION_MODEubuntu
USERNAMEsongvm
INSIDE_EMACS25.2.2,comint
XDG_VTNR2
GIO_LAUNCHED_DESKTOP_FILE_PID6401
SSH_AUTH_SOCK/run/user/1000/keyring/ssh
LC_NAMEzh_CN.UTF-8
XDG_SESSION_ID2
USERsongvm
DESKTOP_SESSIONubuntu
QT4_IM_MODULExim
TEXTDOMAINDIR/usr/share/locale/
PWD/home/songvm/works/xdn/boo
HOME/home/songvm
TEXTDOMAINim-config
SSH_AGENT_PID1535
QT_ACCESSIBILITY1
XDG_SESSION_TYPEx11
XDG_DATA_DIRS/usr/share/ubuntu:/usr/local/share/:/usr/share/:/var/lib/snapd/desktop
XDG_SESSION_DESKTOPubuntu
LC_ADDRESSzh_CN.UTF-8
GJS_DEBUG_OUTPUTstderr
LC_NUMERICzh_CN.UTF-8
GTK_MODULESgail:atk-bridge
COLUMNS80
PAPERSIZEa4
WINDOWPATH2
SHELL/bin/bash
TERMdumb
QT_IM_MODULExim
XMODIFIERSimibus
IM_CONFIG_PHASE2
XDG_CURRENT_DESKTOPubuntu:GNOME
GPG_AGENT_INFO/run/user/1000/gnupg/S.gpg-agent:0:1
GIO_LAUNCHED_DESKTOP_FILE/usr/share/applications/emacs25.desktop
XDG_SEATseat0
SHLVL1
LANGUAGEzh_CN:en
LC_TELEPHONEzh_CN.UTF-8
GDMSESSIONubuntu
GNOME_DESKTOP_SESSION_IDthis-is-deprecated
LOGNAMEsongvm
DBUS_SESSION_BUS_ADDRESSunix:path/run/user/1000/bus
XDG_RUNTIME_DIR/run/user/1000
XAUTHORITY/run/user/1000/gdm/Xauthority
XDG_CONFIG_DIRS/etc/xdg/xdg-ubuntu:/etc/xdg
PATH/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
LC_IDENTIFICATIONzh_CN.UTF-8
GJS_DEBUG_TOPICSJS ERROR;JS LOG
TERMCAP
SESSION_MANAGERlocal/ubuntu:/tmp/.ICE-unix/1458,unix/ubuntu:/tmp/.ICE-unix/1458
LESSOPEN| /usr/bin/lesspipe %s
GTK_IM_MODULEibus
LC_TIMEzh_CN.UTF-8
_./opt
songvmubuntu:~/works/xdn/boo$ 获取某一环境变量的值
以上输出内容挺多在这N个环境变量中如何取单独的某一个环境变量呢如常用的PATHgetenv函数在stdlib.h头文件中定义测试代码如下
/* filename: opt.c */
#include stdio.h
#include stdlib.h/**/
int
main (int argc, char *argv[], char *envp[])
{printf (Get environ variable PATH : [%s]\n, getenv(PATH));return 0;
}编译运行达到预期输出结果如下
songvmubuntu:~/works/xdn/boo$ ./opt
Get environ variable PATH : [/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin]
songvmubuntu:~/works/xdn/boo$ 测试一下内存分配情况发现分配和释放了一次内存无疑是getenv函数所为
songvmubuntu:~/works/xdn/boo$ valgrind --leak-checkyes ./opt
6975 Memcheck, a memory error detector
6975 Copyright (C) 2002-2017, and GNU GPLd, by Julian Seward et al.
6975 Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
6975 Command: ./opt
6975
Get environ variable PATH : [/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin]
6975
6975 HEAP SUMMARY:
6975 in use at exit: 0 bytes in 0 blocks
6975 total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
6975
6975 All heap blocks were freed -- no leaks are possible
6975
6975 For counts of detected and suppressed errors, rerun with: -v
6975 ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
songvmubuntu:~/works/xdn/boo$ 命令行参数的解析相对复杂一些以后再发博文讲解
