--- name: "explain_access" section: "3" platform: "linux" package: "libexplain-dev" version: "1.4.D001-16" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/explain_access" --- # explain\_access(3) explain access(2) errors ## NAME explain\_access - explain [access(2)](/access/2.md) errors ## SYNOPSIS \#include \\ const char \*explain\_access(const char \*pathname, int mode);\ const char \*explain\_errno\_access(int errnum, const char \*pathname, int mode);\ void explain\_message\_access(char \*message, int message\_size, const char \*pathname, int mode);\ void explain\_message\_errno\_access(char \*message, int message\_size, int errnum, const char \*pathname, int mode); ## DESCRIPTION These functions may be used to obtain explanations for [*access*(2)](/access/2.md) errors. ### explain\_access const char \*explain\_access(const char \*pathname, int mode); The explain\_access function is used to obtain an explanation of an error returned by the [*access*(2)](/access/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: ``` int fd = access(pathname, mode); if (fd < 0) { fprintf(stderr, "%s0, explain_access(pathname, mode)); exit(EXIT_FAILURE); } ``` - *pathname* The original pathname, exactly as passed to the [*access*(2)](/access/2.md) system call. - *mode* The original mode, exactly as passed to the [*access*(2)](/access/2.md) system call. TP 8n 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\_access const char \*explain\_errno\_access(int errnum, const char \*pathname, int mode); The explain\_errno\_access function is used to obtain an explanation of an error returned by the [*access*(2)](/access/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: ``` int fd = access(pathname, mode); if (fd < 0) { int err = errno; fprintf(stderr, "%s0, explain_errno_access(err, pathname, mode)); 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*. - *pathname* The original pathname, exactly as passed to the [*access*(2)](/access/2.md) system call. - *mode* The original mode, exactly as passed to the [*access*(2)](/access/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\_access void explain\_message\_access(char \*message, int message\_size, const char \*pathname, int mode); The explain\_message\_access function is used to obtain an explanation of an error returned by the [*access*(2)](/access/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: ``` int fd = access(pathname, mode); if (fd < 0) { char message[3000]; explain_message_access(message, sizeof(message), pathname, mode); fprintf(stderr, "%s0, message); exit(EXIT_FAILURE); } ``` - *message* The location in which to store the returned message. Because a message return buffer has been supplied, this function is thread safe. - *message\_size* The size in bytes of the location in which to store the returned message. - *pathname* The original pathname, exactly as passed to the [*access*(2)](/access/2.md) system call. - *mode* The original mode, exactly as passed to the [*access*(2)](/access/2.md) system call. ### explain\_message\_errno\_access void explain\_message\_errno\_access(char \*message, int message\_size, int errnum, const char \*pathname, int mode); The explain\_message\_errno\_access function is used to obtain an explanation of an error returned by the [*access*(2)](/access/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 exameple: ``` int fd = access(pathname, mode); if (fd < 0) { int err = errno; char message[3000]; explain_message_errno_access(message, sizeof(message), err, pathname, mode); fprintf(stderr, "%s0, message); exit(EXIT_FAILURE); } ``` - *message* The location in which to store the returned message. Because a message return buffer has been 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*. - *pathname* The original pathname, exactly as passed to the [*access*(2)](/access/2.md) system call. - *mode* The original mode, exactly as passed to the [*access*(2)](/access/2.md) system call. ## COPYRIGHT libexplain version 1.4\ Copyright (C) 2008 Peter Miller ## AUTHOR Written by Peter Miller \