--- name: "explain_freopen" section: "3" platform: "linux" package: "libexplain-dev" version: "1.4.D001-16" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/explain_freopen" --- # explain\_freopen(3) explain freopen(3) errors ## NAME explain\_freopen - explain [freopen(3)](/freopen/3.md) errors ## SYNOPSIS \#include \\ const char \*explain\_freopen(const char \*pathname, const char \*flags, FILE \*fp);\ const char \*explain\_errno\_freopen(int errnum, const char \*pathname, const char \*flags, FILE \*fp);\ void explain\_message\_freopen(char \*message, int message\_size, const char \*pathname, const char \*flags, FILE \*fp);\ void explain\_message\_errno\_freopen(char \*message, int message\_size, int errnum, const char \*pathname, const char \*flags, FILE \*fp); ## DESCRIPTION These functions may be used to obtain explanations for [*freopen*(3)](/freopen/3.md) errors. ### explain\_freopen const char \*explain\_freopen(const char \*pathname, const char \*flags, FILE \*fp); The explain\_freopen function is used to obtain an explanation of an error returned by the [*freopen*(3)](/freopen/3.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 (!freopen(pathname, flags, fp)) { fprintf(stderr, '%s0, explain_freopen(pathname, flags, fp)); exit(EXIT_FAILURE); } ``` - *pathname* The original pathname, exactly as passed to the [*freopen*(3)](/freopen/3.md) system call. - *flags* The original flags, exactly as passed to the [*freopen*(3)](/freopen/3.md) system call. - *fp* The original fp, exactly as passed to the [*freopen*(3)](/freopen/3.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\_freopen const char \*explain\_errno\_freopen(int errnum, const char \*pathname, const char \*flags, FILE \*fp); The explain\_errno\_freopen function is used to obtain an explanation of an error returned by the [*freopen*(3)](/freopen/3.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 (freopen(pathname, flags, fp)) { int err = errno; fprintf(stderr, '%s0, explain_errno_freopen(err, pathname, flags, fp)); 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 [*freopen*(3)](/freopen/3.md) system call. - *flags* The original flags, exactly as passed to the [*freopen*(3)](/freopen/3.md) system call. - *fp* The original fp, exactly as passed to the [*freopen*(3)](/freopen/3.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\_freopen void explain\_message\_freopen(char \*message, int message\_size, const char \*pathname, const char \*flags, FILE \*fp); The explain\_message\_freopen function is used to obtain an explanation of an error returned by the [*freopen*(3)](/freopen/3.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 (!freopen(pathname, flags, fp)) { char message[3000]; explain_message_freopen(message, sizeof(message), pathname, flags, fp); 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 [*freopen*(3)](/freopen/3.md) system call. - *flags* The original flags, exactly as passed to the [*freopen*(3)](/freopen/3.md) system call. - *fp* The original fp, exactly as passed to the [*freopen*(3)](/freopen/3.md) system call. ### explain\_message\_errno\_freopen void explain\_message\_errno\_freopen(char \*message, int message\_size, int errnum, const char \*pathname, const char \*flags, FILE \*fp); The explain\_message\_errno\_freopen function is used to obtain an explanation of an error returned by the [*freopen*(3)](/freopen/3.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 (!freopen(pathname, flags, fp)) { int err = errno; char message[3000]; explain_message_errno_freopen(message, sizeof(message), err, pathname, flags, fp); 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 [*freopen*(3)](/freopen/3.md) system call. - *flags* The original flags, exactly as passed to the [*freopen*(3)](/freopen/3.md) system call. - *fp* The original fp, exactly as passed to the [*freopen*(3)](/freopen/3.md) system call. ## COPYRIGHT libexplain version 1.4\ Copyright (C) 2008 Peter Miller ## AUTHOR Written by Peter Miller \