linux下的argv与environ变量
2017-08-29 13:54
316 查看
先看代码
执行结果如下:
从打印的结果可以看出,environ变量的内存紧跟在argv变量内存的后面。argv最后一个指针指向“def”------0x7fffb80f5613:def, environ第一个指针指向0x7fffb80f5617:ORBIT_SOCKETDIR=/tmp/orbit-lgh,它们相差了四个字节即“def\0”,\0是C语言字符串结束标记。
并且也可打印了“========== ptr equals environ ==========”, 所以结论是:environ = argv + argc + 1,其中1是argv结束的NULL指针,并且它们指向的数据存储在连续的内存块中。
reference:
https://stackoverflow.com/questions/6203455/why-i-cant-print-out-environment-variables-in-gdb
#include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) { extern char **environ; int i=0; while( argv[i] != NULL ) { printf("%p:%s\n", argv[i], argv[i]); i++; } printf("%p:%s\n\n", argv[i], argv[i]); i=0; char **ptr = argv + argc + 1; /* points to environment, in Un*x */ if ( ptr == environ ) { printf("========== ptr equals environ ==========\n\n"); } while( environ[i] != NULL ) { printf("%p:%s\n", environ[i], environ[i]); i++; } return 0; }
执行结果如下:
[root@lghvm001 tiny_test]# ./a.out a bc def 0x7fffb80f5606:./a.out 0x7fffb80f560e:a 0x7fffb80f5610:bc 0x7fffb80f5613:def (nil):(null) ========== ptr equals environ ========== 0x7fffb80f5617:ORBIT_SOCKETDIR=/tmp/orbit-lgh 0x7fffb80f5636:HOSTNAME=lghvm001 0x7fffb80f5648:TERM=xterm 0x7fffb80f5653:SHELL=/bin/bash 0x7fffb80f5663:XDG_SESSION_COOKIE=c1fc12fdd7c4455c71686ae40000000e-1481541048.731078-183755250 0x7fffb80f56b3:HISTSIZE=1000 0x7fffb80f56c1:GTK_RC_FILES=/etc/gtk/gtkrc:/home/lgh/.gtkrc-1.2-gnome2 0x7fffb80f56f9:WINDOWID=49124397 0x7fffb80f570b:OLDPWD=/home/lgh/lgh/lgh_dev 0x7fffb80f5728:USER=root 0x7fffb80f5732:LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=01;05;37;41:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arj=01;31:*.taz=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31:*.gz=01;31:*.lz=01;31:*.xz=01;31:*.bz2=01;31:*.tbz=01;31:*.tbz2=01;31:*.bz=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.rar=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.jpg=01;35:*.jpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.axv=01;35:*.anx=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=01;36:*.au=01;36:*.flac=01;36:*.mid=01;36:*.midi=01;36:*.mka=01;36:*.mp3=01;36:*.mpc=01;36:*.ogg=01;36:*.ra=01;36:*.wav=01;36:*.axa=01;36:*.oga=01;36:*.spx=01;36:*.xspf=01;36: 0x7fffb80f5c31:GNOME_KEYRING_SOCKET=/tmp/keyring-kebjUP/socket 0x7fffb80f5c61:SSH_AUTH_SOCK=/tmp/keyring-kebjUP/socket.ssh 0x7fffb80f5c8e:SESSION_MANAGER=local/unix:@/tmp/.ICE-unix/2513,unix/unix:/tmp/.ICE-unix/2513 0x7fffb80f5cdc:USERNAME=lgh 0x7fffb80f5ce9:DESKTOP_SESSION=gnome 0x7fffb80f5cff:MAIL=/var/spool/mail/root 0x7fffb80f5d19:PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/home/lgh/bin:/usr/local/go/bin:/usr/local/openresty/nginx/sbin:/usr/local/go/bin:/usr/local/openresty/nginx/sbin:/usr/local/go/bin 0x7fffb80f5ddf:PWD=/home/lgh/lgh/lgh_dev/tiny_test 0x7fffb80f5e03:GDM_KEYBOARD_LAYOUT=us 0x7fffb80f5e1a:LANG=en_US.utf8 0x7fffb80f5e2a:GNOME_KEYRING_PID=2504 0x7fffb80f5e41:GDM_LANG=en_US.utf8 0x7fffb80f5e55:GDMSESSION=gnome 0x7fffb80f5e66:SSH_ASKPASS=/usr/libexec/openssh/gnome-ssh-askpass 0x7fffb80f5e99:HISTCONTROL=ignoredups 0x7fffb80f5eb0:HOME=/root 0x7fffb80f5ebb:SHLVL=3 0x7fffb80f5ec3:GNOME_DESKTOP_SESSION_ID=this-is-deprecated 0x7fffb80f5eef:LOGNAME=root 0x7fffb80f5efc:DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-FozvquakWJ,guid=75674d80ad97ff2c8a2798a400000025 0x7fffb80f5f5e:LESSOPEN=|/usr/bin/lesspipe.sh %s 0x7fffb80f5f80:WINDOWPATH=1 0x7fffb80f5f8d:DISPLAY=:0.0 0x7fffb80f5f9a:G_BROKEN_FILENAMES=1 0x7fffb80f5faf:XAUTHORITY=/root/.xauthnETzkC 0x7fffb80f5fcd:COLORTERM=gnome-terminal 0x7fffb80f5fe6:_=./a.out [root@lghvm001 tiny_test]#
从打印的结果可以看出,environ变量的内存紧跟在argv变量内存的后面。argv最后一个指针指向“def”------0x7fffb80f5613:def, environ第一个指针指向0x7fffb80f5617:ORBIT_SOCKETDIR=/tmp/orbit-lgh,它们相差了四个字节即“def\0”,\0是C语言字符串结束标记。
并且也可打印了“========== ptr equals environ ==========”, 所以结论是:environ = argv + argc + 1,其中1是argv结束的NULL指针,并且它们指向的数据存储在连续的内存块中。
reference:
https://stackoverflow.com/questions/6203455/why-i-cant-print-out-environment-variables-in-gdb
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