The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
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realpath - resolve a pathname


[XSI] [Option Start] #include <stdlib.h>

char *realpath(const char *restrict
       char *restrict
resolved_name); [Option End]


The realpath() function shall derive, 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 shall be stored as a null-terminated string, up to a maximum of {PATH_MAX} bytes, in the buffer pointed to by resolved_name.

If resolved_name is a null pointer, the behavior of realpath() is implementation-defined.


Upon successful completion, realpath() shall return a pointer to the resolved name. Otherwise, realpath() shall return a null pointer and set errno to indicate the error, and the contents of the buffer pointed to by resolved_name are undefined.


The realpath() function shall fail if:

Read or search permission was denied for a component of file_name.
The file_name argument is a null pointer.
An error occurred while reading from the file system.
A loop exists in symbolic links encountered during resolution of the file_name argument.
The length of the file_name argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.
A component of file_name does not name an existing file or file_name points to an empty string.
A component of the path prefix is not a directory.

The realpath() function may fail if:

More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the file_name argument.
Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.
Insufficient storage space is available.

The following sections are informative.


Generating an Absolute Pathname

The following example generates an absolute pathname for the file identified by the symlinkpath argument. The generated pathname is stored in the actualpath array.

#include <stdlib.h>
char *symlinkpath = "/tmp/symlink/file";
char actualpath [PATH_MAX+1];
char *ptr;

ptr = realpath(symlinkpath, actualpath);




Since the maximum pathname length is arbitrary unless {PATH_MAX} is defined, an application generally cannot supply a resolved_name buffer with size {{PATH_MAX}+1}.


In the future, passing a null pointer to realpath() for the resolved_name argument may be defined to have realpath() allocate space for the generated pathname.


getcwd(), sysconf(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>


First released in Issue 4, Version 2.

Issue 5

Moved from X/OPEN UNIX extension to BASE.

Issue 6

The restrict keyword is added to the realpath() prototype for alignment with the ISO/IEC 9899:1999 standard.

The wording of the mandatory [ELOOP] error condition is updated, and a second optional [ELOOP] error condition is added.

IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/51 is applied, adding new text to the DESCRIPTION for the case when resolved_name is a null pointer, changing the [EINVAL] error text, adding text to the RATIONALE, and adding text to FUTURE DIRECTIONS.

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/110 is applied, updating the ERRORS section to refer to the file_name argument, rather than a non-existent path argument.

End of informative text.

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