86 lines
1.7 KiB
Text
86 lines
1.7 KiB
Text
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.TH ERRSTR 2
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.SH NAME
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errstr, rerrstr, werrstr \- description of last system call error
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.B
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int errstr(char *err, uint nerr)
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.PP
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.B
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void rerrstr(char *err, uint nerr)
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.PP
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.B
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void werrstr(char *fmt, ...)
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.SH DESCRIPTION
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When a system call fails it returns \-1 and
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records a null terminated string describing the error in a per-process buffer.
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.I Errstr
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swaps the contents of that buffer with the contents of the array
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.IR err .
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.I Errstr
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will write at most
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.I nerr
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bytes into
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.IR err ;
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if the per-process error string does not fit,
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it is silently truncated at a UTF character boundary.
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The returned string is NUL-terminated.
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Usually
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.I errstr
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will be called with an empty string,
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but the exchange property provides a mechanism for
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libraries to set the return value for the next call to
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.IR errstr .
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.PP
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The per-process buffer is
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.B ERRMAX
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bytes long. Any error string provided by the user will
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be truncated at
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.B ERRMAX-1
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bytes.
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.B ERRMAX
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is defined in
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.BR <libc.h> .
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.PP
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If no system call has generated an error since the last call to
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.I errstr
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with an empty string,
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the result is an empty string.
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.PP
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The verb
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.B r
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in
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.IR print (2)
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calls
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.I errstr
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and outputs the error string.
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.PP
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.I Rerrstr
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reads the error string but does not modify the per-process buffer, so
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a subsequent
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.I errstr
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will recover the same string.
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.PP
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.I Werrstr
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takes a
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.I print
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style format as its argument and uses it to format
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a string to pass to
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.IR errstr .
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The string returned from
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.I errstr
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is discarded.
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.SH SOURCE
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.B /sys/src/libc/9syscall
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.br
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.B /sys/src/libc/9sys/werrstr.c
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.SH DIAGNOSTICS
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.I Errstr
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always returns 0.
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.SH SEE ALSO
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.IR intro (2),
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.IR perror (2)
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