[quote user="Mohammad Aryafar"]I'm trying to open a simple text file[/quote]
Prefer to use the mdlTextFile_api.
[quote user="Mohammad Aryafar"]if (fopen_s(&fp , "text.txt","r") == 0)[/quote]
You probably need a full file specification...
FILE* fp = mdlTextFile_open ("C:\\temp\\text.txt", TEXTFILE_READ);
if (fp) {
...
mdlTextFile_close (fp);
}[quote user="Mohammad Aryafar"]Unresolved symbol xxx[/quote]
The linker is telling you that it can't find the implementation of xxx in any of the library files you have specified. Look at the bmake (*.mke) files in the examples delivered with the SDK for more detail.