SIMPLE SOLUTIONS

EXPLAIN_FSEEK(3) - man page online | library functions

Explain fseek(3) errors.

Chapter
explain_fseek(3)                     Library Functions Manual                    explain_fseek(3)

NAME explain_fseek - explain fseek(3) errors
SYNOPSIS #include <libexplain/fseek.h> const char *explain_fseek(FILE *fp, long offset, int whence); const char *explain_errno_fseek(int errnum, FILE *fp, long offset, int whence); void explain_message_fseek(char *message, int message_size, FILE *fp, long offset, int whence); void explain_message_errno_fseek(char *message, int message_size, int errnum, FILE *fp, long offset, int whence);
DESCRIPTION These functions may be used to obtain explanations for errors returned by the fseek(3) system call. explain_fseek const char *explain_fseek(FILE *fp, long offset, int whence); The explain_fseek function is used to obtain an explanation of an error returned by the fseek(3) 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. fp The original fp, exactly as passed to the fseek(3) system call. offset The original offset, exactly as passed to the fseek(3) system call. whence The original whence, exactly as passed to the fseek(3) 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 over‐ written 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. Example: This function is intended to be used in a fashion similar to the following exam‐ ple: if (fseek(fp, offset, whence) < 0) { fprintf(stderr, "%s\n", explain_fseek(fp, offset, whence)); exit(EXIT_FAILURE); } The above code example is available pre‐packaged as the explain_fseek_or_die(3) function. explain_errno_fseek const char *explain_errno_fseek(int errnum, FILE *fp, long offset, int whence); The explain_errno_fseek function is used to obtain an explanation of an error returned by the fseek(3) system call. The least the message will contain is the value of str‐ error(errno), but usually it will do much better, and indicate the underlying cause in more detail. 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. fp The original fp, exactly as passed to the fseek(3) system call. offset The original offset, exactly as passed to the fseek(3) system call. whence The original whence, exactly as passed to the fseek(3) 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 over‐ written 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. Example: This function is intended to be used in a fashion similar to the following exam‐ ple: if (fseek(fp, offset, whence) < 0) { int err = errno; fprintf(stderr, "%s\n", explain_errno_fseek(err, fp, offset, whence)); exit(EXIT_FAILURE); } The above code example is available pre‐packaged as the explain_fseek_or_die(3) function. explain_message_fseek void explain_message_fseek(char *message, int message_size, FILE *fp, long offset, int whence); The explain_message_fseek function is used to obtain an explanation of an error returned by the fseek(3) system call. The least the message will contain is the value of str‐ error(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. 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. fp The original fp, exactly as passed to the fseek(3) system call. offset The original offset, exactly as passed to the fseek(3) system call. whence The original whence, exactly as passed to the fseek(3) system call. Example: This function is intended to be used in a fashion similar to the following exam‐ ple: if (fseek(fp, offset, whence) < 0) { char message[3000]; explain_message_fseek(message, sizeof(message), fp, offset, whence); fprintf(stderr, "%s\n", message); exit(EXIT_FAILURE); } The above code example is available pre‐packaged as the explain_fseek_or_die(3) function. explain_message_errno_fseek void explain_message_errno_fseek(char *message, int message_size, int errnum, FILE *fp, long offset, int whence); The explain_message_errno_fseek function is used to obtain an explanation of an error returned by the fseek(3) 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. 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. fp The original fp, exactly as passed to the fseek(3) system call. offset The original offset, exactly as passed to the fseek(3) system call. whence The original whence, exactly as passed to the fseek(3) system call. Example: This function is intended to be used in a fashion similar to the following exam‐ ple: if (fseek(fp, offset, whence) < 0) { int err = errno; char message[3000]; explain_message_errno_fseek(message, sizeof(message), err, fp, offset, whence); fprintf(stderr, "%s\n", message); exit(EXIT_FAILURE); } The above code example is available pre‐packaged as the explain_fseek_or_die(3) function.
SEE ALSO fseek(3) reposition a stream explain_fseek_or_die(3) reposition a stream and report errors
explain_fseek(3)
This manual Reference Other manuals
explain_fseek(3) referred by explain(3) | explain_fseek_or_die(3)
refer to explain_fseek_or_die(3) | fseek(3)