--- name: "explain_readdir" section: "3" platform: "linux" package: "libexplain-dev" version: "1.4.D001-16" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/explain_readdir" --- # explain\_readdir(3) explain readdir(2) errors ## NAME explain\_readdir - explain [readdir(2)](/readdir/2.md) errors ## SYNOPSIS \#include \ const char \*explain\_readdir(DIR \*dir);\ const char \*explain\_errno\_readdir(int errnum, DIR \*dir);\ void explain\_message\_readdir(char \*message, int message\_size, DIR \*dir);\ void explain\_message\_errno\_readdir(char \*message, int message\_size, int errnum, DIR \*dir); ## DESCRIPTION These functions may be used to obtain explanations for errors returned by the [*readdir*(2)](/readdir/2.md) system call. ### explain\_readdir const char \*explain\_readdir(DIR \*dir); The **explain\_readdir** function is used to obtain an explanation of an error returned by the [*readdir*(2)](/readdir/2.md) system call. The least the message will contain is the value of `strerror(errno)`, but usually it will do much better, and indicate the underlying cause in more detail. The *errno* global variable will be used to obtain the error value to be decoded. This function is intended to be used in a fashion similar to the following example: ``` errno = 0; struct dirent *dep = readdir(dir); if (!dep && errno != 0) { fprintf(stderr, "%s\n", explain_readdir(dir)); exit(EXIT_FAILURE); } ``` - *dir* The original dir, exactly as passed to the [*readdir*(2)](/readdir/2.md) system call. - Returns: The message explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads. **Note:** This function is **not** thread safe, because it shares a return buffer across all threads, and many other functions in this library. ### explain\_errno\_readdir const char \*explain\_errno\_readdir(int errnum, DIR \*dir); The **explain\_errno\_readdir** function is used to obtain an explanation of an error returned by the [*readdir*(2)](/readdir/2.md) system call. The least the message will contain is the value of `strerror(errnum)`, but usually it will do much better, and indicate the underlying cause in more detail. This function is intended to be used in a fashion similar to the following example: ``` errno = 0; struct dirent *dep = readdir(dir); int err = errno; if (!dep && errno != 0) { fprintf(stderr, "%s\n", explain_errno_readdir(err, dir)); exit(EXIT_FAILURE); } ``` - *errnum* The error value to be decoded, usually obtained from the *errno* global variable just before this function is called. This is necessary if you need to call **any** code between the system call to be explained and this function, because many libc functions will alter the value of *errno*. - *dir* The original dir, exactly as passed to the [*readdir*(2)](/readdir/2.md) system call. - Returns: The message explaining the error. This message buffer is shared by all libexplain functions which do not supply a buffer in their argument list. This will be overwritten by the next call to any libexplain function which shares this buffer, including other threads. **Note:** This function is **not** thread safe, because it shares a return buffer across all threads, and many other functions in this library. ### explain\_message\_readdir void explain\_message\_readdir(char \*message, int message\_size, DIR \*dir); The **explain\_message\_readdir** function may be used to obtain an explanation of an error returned by the [*readdir*(2)](/readdir/2.md) system call. The least the message will contain is the value of `strerror(errno)`, but usually it will do much better, and indicate the underlying cause in more detail. The *errno* global variable will be used to obtain the error value to be decoded. This function is intended to be used in a fashion similar to the following example: ``` errno = 0; struct dirent *dep = readdir(dir); if (!dep && errno != 0) { char message[3000]; explain_message_readdir(message, sizeof(message), dir); fprintf(stderr, "%s\n", message); exit(EXIT_FAILURE); } ``` - *message* The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe. - *message\_size* The size in bytes of the location in which to store the returned message. - *dir* The original dir, exactly as passed to the [*readdir*(2)](/readdir/2.md) system call. ### explain\_message\_errno\_readdir void explain\_message\_errno\_readdir(char \*message, int message\_size, int errnum, DIR \*dir); The **explain\_message\_errno\_readdir** function may be used to obtain an explanation of an error returned by the [*readdir*(2)](/readdir/2.md) system call. The least the message will contain is the value of `strerror(errnum)`, but usually it will do much better, and indicate the underlying cause in more detail. This function is intended to be used in a fashion similar to the following example: ``` errno = 0; struct dirent *dep = readdir(dir); int err = errno; if (!dep && errno != 0) { char message[3000]; explain_message_errno_readdir(message, sizeof(message), err, dir); fprintf(stderr, "%s\n", message); exit(EXIT_FAILURE); } ``` - *message* The location in which to store the returned message. If a suitable message return buffer is supplied, this function is thread safe. - *message\_size* The size in bytes of the location in which to store the returned message. - *errnum* The error value to be decoded, usually obtained from the *errno* global variable just before this function is called. This is necessary if you need to call **any** code between the system call to be explained and this function, because many libc functions will alter the value of *errno*. - *dir* The original dir, exactly as passed to the [*readdir*(2)](/readdir/2.md) system call. ## SEE ALSO - [*readdir*(2)](/readdir/2.md) read directory entry - [*explain\_readdir\_or\_die*(3)](/explain_readdir_or_die/3.md) read directory entry and report errors ## COPYRIGHT libexplain version 1.4\ Copyright (C) 2008 Peter Miller