@sumeyye , not easy to know why you have the shown "linker error" .....
Could be you are reusing an already trashed ns-2.35 ?
You can have as many times ns-allinone-2.xx as you want, installed at the same time ...
..... so simply unpack a new one to a new directory .....
/home/name/ns2/a/ns-allinone-2.35/
/home/name/ns2/b/ns-allinone-2.35/
/home/name/ns2/c/ns-allinone-2.35/
/home/name/ns2/d/ns-allinone-2.35/
.
/home/name/ns2/x/ns-allinone-2.35/
..... i.e no limit .... .... so just continue till you get it right .....
cd ns-allinone-2.35/
export CC=gcc-4.8 CXX=g++-4.8 && ./install
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Note: "You should avoid posting pictures of text. Pictures can be hard to read. Text is easier to read in different screen formats, can be copied and pasted, as well as is search engine addressable, making it easier for people to reach this post who may have a similar issue."
My comments : I guess you know how to copy-paste a text.
And : Images will often not be read.