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| .TH READDIR_R 3 2021-03-22 "" "Linux Programmer's Manual" |
| .SH NAME |
| readdir_r \- read a directory |
| .SH SYNOPSIS |
| .nf |
| .B #include <dirent.h> |
| .PP |
| .BI "int readdir_r(DIR *restrict " dirp ", struct dirent *restrict " entry , |
| .BI " struct dirent **restrict " result ); |
| .fi |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR readdir_r (): |
| .nf |
| _POSIX_C_SOURCE |
| || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .fi |
| .SH DESCRIPTION |
| This function is deprecated; use |
| .BR readdir (3) |
| instead. |
| .PP |
| The |
| .BR readdir_r () |
| function was invented as a reentrant version of |
| .BR readdir (3). |
| It reads the next directory entry from the directory stream |
| .IR dirp , |
| and returns it in the caller-allocated buffer pointed to by |
| .IR entry . |
| For details of the |
| .IR dirent |
| structure, see |
| .BR readdir (3). |
| .PP |
| A pointer to the returned buffer is placed in |
| .IR *result ; |
| if the end of the directory stream was encountered, |
| then NULL is instead returned in |
| .IR *result . |
| .PP |
| It is recommended that applications use |
| .BR readdir (3) |
| instead of |
| .BR readdir_r (). |
| Furthermore, since version 2.24, glibc deprecates |
| .BR readdir_r (). |
| The reasons are as follows: |
| .IP * 3 |
| On systems where |
| .BR NAME_MAX |
| is undefined, calling |
| .BR readdir_r () |
| may be unsafe because the interface does not allow the caller to specify |
| the length of the buffer used for the returned directory entry. |
| .IP * |
| On some systems, |
| .BR readdir_r () |
| can't read directory entries with very long names. |
| When the glibc implementation encounters such a name, |
| .BR readdir_r () |
| fails with the error |
| .B ENAMETOOLONG |
| .IR "after the final directory entry has been read" . |
| On some other systems, |
| .BR readdir_r () |
| may return a success status, but the returned |
| .IR d_name |
| field may not be null terminated or may be truncated. |
| .IP * |
| In the current POSIX.1 specification (POSIX.1-2008), |
| .BR readdir (3) |
| is not required to be thread-safe. |
| However, in modern implementations (including the glibc implementation), |
| concurrent calls to |
| .BR readdir (3) |
| that specify different directory streams are thread-safe. |
| Therefore, the use of |
| .BR readdir_r () |
| is generally unnecessary in multithreaded programs. |
| In cases where multiple threads must read from the same directory stream, |
| using |
| .BR readdir (3) |
| with external synchronization is still preferable to the use of |
| .BR readdir_r (), |
| for the reasons given in the points above. |
| .IP * |
| It is expected that a future version of POSIX.1 |
| .\" FIXME . |
| .\" http://www.austingroupbugs.net/view.php?id=696 |
| will make |
| .BR readdir_r () |
| obsolete, and require that |
| .BR readdir (3) |
| be thread-safe when concurrently employed on different directory streams. |
| .SH RETURN VALUE |
| The |
| .BR readdir_r () |
| function returns 0 on success. |
| On error, it returns a positive error number (listed under ERRORS). |
| If the end of the directory stream is reached, |
| .BR readdir_r () |
| returns 0, and returns NULL in |
| .IR *result . |
| .SH ERRORS |
| .TP |
| .B EBADF |
| Invalid directory stream descriptor \fIdirp\fP. |
| .TP |
| .B ENAMETOOLONG |
| A directory entry whose name was too long to be read was encountered. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR readdir_r () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| POSIX.1-2001, POSIX.1-2008. |
| .SH SEE ALSO |
| .BR readdir (3) |