--- name: "explain_setsockopt" section: "3" platform: "linux" package: "libexplain-dev" version: "1.4.D001-16" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/explain_setsockopt" --- # explain\_setsockopt(3) explain setsockopt(2) errors ## NAME explain\_setsockopt - explain [setsockopt(2)](/setsockopt/2.md) errors ## SYNOPSIS \#include \ const char \*explain\_setsockopt(int fildes, int level, int name, void \*data, socklen\_t data\_size);\ const char \*explain\_errno\_setsockopt(int errnum, int fildes, int level, int name, void \*data, socklen\_t data\_size);\ void explain\_message\_setsockopt(char \*message, int message\_size, int fildes, int level, int name, void \*data, socklen\_t data\_size);\ void explain\_message\_errno\_setsockopt(char \*message, int message\_size, int errnum, int fildes, int level, int name, void \*data, socklen\_t data\_size); ## DESCRIPTION These functions may be used to obtain explanations for errors returned by the [*setsockopt*(2)](/setsockopt/2.md) system call. ### explain\_setsockopt const char \*explain\_setsockopt(int fildes, int level, int name, void \*data, socklen\_t data\_size); The **explain\_setsockopt** function is used to obtain an explanation of an error returned by the [*setsockopt*(2)](/setsockopt/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: ``` if (setsockopt(fildes, level, name, data, data_size) < 0) { fprintf(stderr, "%s\n", explain_setsockopt(fildes, level, name, data, data_size)); exit(EXIT_FAILURE); } ``` The above code example is available pre‐packaged as the [*explain\_setsockopt\_or\_die*(3)](/explain_setsockopt_or_die/3.md) function. - *fildes* The original fildes, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *level* The original level, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *name* The original name, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *data* The original data, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *data\_size* The original data\_size, exactly as passed to the [*setsockopt*(2)](/setsockopt/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\_setsockopt const char \*explain\_errno\_setsockopt(int errnum, int fildes, int level, int name, void \*data, socklen\_t data\_size); The **explain\_errno\_setsockopt** function is used to obtain an explanation of an error returned by the [*setsockopt*(2)](/setsockopt/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: ``` if (setsockopt(fildes, level, name, data, data_size) < 0) { int err = errno; fprintf(stderr, "%s\n", explain_errno_setsockopt(err, fildes, level, name, data, data_size)); exit(EXIT_FAILURE); } ``` The above code example is available pre‐packaged as the [*explain\_setsockopt\_or\_die*(3)](/explain_setsockopt_or_die/3.md) function. - *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*. - *fildes* The original fildes, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *level* The original level, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *name* The original name, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *data* The original data, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *data\_size* The original data\_size, exactly as passed to the [*setsockopt*(2)](/setsockopt/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\_setsockopt void explain\_message\_setsockopt(char \*message, int message\_size, int fildes, int level, int name, void \*data, socklen\_t data\_size); The **explain\_message\_setsockopt** function may be used to obtain an explanation of an error returned by the [*setsockopt*(2)](/setsockopt/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: ``` if (setsockopt(fildes, level, name, data, data_size) < 0) { char message[3000]; explain_message_setsockopt(message, sizeof(message), fildes, level, name, data, data_size); fprintf(stderr, "%s\n", message); exit(EXIT_FAILURE); } ``` The above code example is available pre‐packaged as the [*explain\_setsockopt\_or\_die*(3)](/explain_setsockopt_or_die/3.md) function. - *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. - *fildes* The original fildes, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *level* The original level, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *name* The original name, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *data* The original data, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *data\_size* The original data\_size, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. ### explain\_message\_errno\_setsockopt void explain\_message\_errno\_setsockopt(char \*message, int message\_size, int errnum, int fildes, int level, int name, void \*data, socklen\_t data\_size); The **explain\_message\_errno\_setsockopt** function may be used to obtain an explanation of an error returned by the [*setsockopt*(2)](/setsockopt/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: ``` if (setsockopt(fildes, level, name, data, data_size) < 0) { int err = errno; char message[3000]; explain_message_errno_setsockopt(message, sizeof(message), err, fildes, level, name, data, data_size); fprintf(stderr, "%s\n", message); exit(EXIT_FAILURE); } ``` The above code example is available pre‐packaged as the [*explain\_setsockopt\_or\_die*(3)](/explain_setsockopt_or_die/3.md) function. - *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*. - *fildes* The original fildes, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *level* The original level, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *name* The original name, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *data* The original data, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. - *data\_size* The original data\_size, exactly as passed to the [*setsockopt*(2)](/setsockopt/2.md) system call. ## SEE ALSO - [*setsockopt*(2)](/setsockopt/2.md) get and set options on sockets - [*explain\_setsockopt\_or\_die*(3)](/explain_setsockopt_or_die/3.md) get and set options on sockets and report errors ## COPYRIGHT libexplain version 1.4\ Copyright (C) 2009 Peter Miller