The realpath() function derives, from the pathname pointed to by file_name, an absolute pathname that names the same file, whose resolution does not involve ".", "..", or symbolic links. The generated pathname, using PATH_MAX bytes, is stored in the buffer pointed to by resolved_name.

The realpath() function can handle both relative and absolute path names. For absolute path names and the relative names whose resolved name cannot be expressed relatively (for example, ../../reldir), it returns the resolved absolute name. For the other relative path names, it returns the resolved relative name.

On successful completion, realpath() returns a pointer to the resolved name. Otherwise, realpath() returns a null pointer and sets errno to indicate the error, and the contents of the buffer pointed to by resolved_name are undefined.

The realpath() function will fail if:

EACCES

Read or search permission was denied for a component of file_name.

EINVAL

Either the file_name or resolved_name argument is a null pointer.

EIO

An error occurred while reading from the file system.

ELOOP

Too many symbolic links were encountered in resolving path.

ENAMETOOLONG

The file_name argument is longer than PATH_MAX or a pathname component is longer than NAME_MAX.

ENOENT

A component of file_name does not name an existing file or file_name points to an empty string.

ENOTDIR

A component of the path prefix is not a directory.

The realpath() function may fail if:

ENAMETOOLONG

Pathname resolution of a symbolic link produced an intermediate result whose length exceeds PATH_MAX.

ENOMEM

Insufficient storage space is available.

The realpath() function operates on null-terminated strings.

One should have execute permission on all the directories in the given and the resolved path.

The realpath() function may fail to return to the current directory if an error occurs.

See attributes(5) for descriptions of the following attributes:

getcwd(3C), sysconf(3C), attributes(5)