The realpath function resolves all symbolic links, extra "/" characters and references to /./ and /../ in pathname, and copies the resulting absolute pathname into the memory referenced by resolved_path. The resolved_path argument must refer to a buffer capable of storing at least PATH_MAX characters.
The realpath function will resolve both absolute and relative paths and return the absolute pathname corresponding to pathname. All but the last component of pathname must exist when realpath is called.
The realpath function returns resolved_path on success. If an error occurs, realpath returns NULL, and resolved_path contains the pathname which caused the problem.
The function realpath may fail and set the external variable errno for any of the errors specified for the library functions lstat(2), readlink(2) and getcwd(3).
This implementation of realpath differs slightly from the Solaris implementation. The BSD 4.4 version always returns absolute pathnames, whereas the Solaris implementation will, under certain circumstances, return a relative resolved_path when given a relative pathname.