C++ how to get the absolute file path from iOS Cache directory

With code below I able to access cache folder in my app. I think, documents folder in "/Library/Documents", or somewhere else.

char *home = getenv("HOME");
char *subdir = "/Library/Caches/subdir";

char fullpath[200];

strcpy(fullpath,home);

strcat(fullpath, subdir);

Next, with full path, you can do usual things to read/write in C++

references:
http://stackoverflow.com/questions/13469342/using-c-to-access-documents-folder-on-ios