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d4a1283797
Summary of changes:
* Make xvsnprintf() static
* restrict-qualify pointer arguments (as done by the libc equivalents)
* Make comments and spec references more thorough
* Remove pointless `n <= INT_MAX` assertion (see comment)
* Use FATAL_ERROR() instead of xassert() (since the assertion is inside
a shared util function but the caller is responsible for ensuring the
condition holds true)
* Change some callers to use size_t instead of int for the return value
(negative returns are impossible and all subsequent uses are size_t)
The updated comments and code were taken (and adapted) from:
49260bb154/src/util/xsnprintf.c (L6-50)
This work was entirely authored by me and I hereby license this
contribution under the MIT license (stated explicitly, so that
there's no ambiguity w.r.t. the original license).
55 lines
1.6 KiB
C
55 lines
1.6 KiB
C
#include "xsnprintf.h"
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#include <errno.h>
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#include <limits.h>
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#include <stdio.h>
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#include "debug.h"
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#include "macros.h"
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/*
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* ISO C doesn't require vsnprintf(3) to set errno on failure, but
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* POSIX does:
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*
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* "If an output error was encountered, these functions shall return
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* a negative value and set errno to indicate the error."
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*
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* The mandated errors of interest are:
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*
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* - EILSEQ: A wide-character code does not correspond to a valid character
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* - EOVERFLOW: The value of n is greater than INT_MAX
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* - EOVERFLOW: The value to be returned is greater than INT_MAX
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*
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* ISO C11 states:
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*
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* "The vsnprintf function returns the number of characters that would
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* have been written had n been sufficiently large, not counting the
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* terminating null character, or a negative value if an encoding error
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* occurred. Thus, the null-terminated output has been completely
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* written if and only if the returned value is nonnegative and less
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* than n."
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*
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* See also:
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*
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* - ISO C11 §7.21.6.12p3
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* - https://pubs.opengroup.org/onlinepubs/9699919799/functions/vsnprintf.html
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* - https://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html
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*/
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static size_t
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xvsnprintf(char *restrict buf, size_t n, const char *restrict format, va_list ap)
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{
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int len = vsnprintf(buf, n, format, ap);
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if (unlikely(len < 0 || len >= (int)n)) {
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FATAL_ERROR(__func__, (len < 0) ? errno : ENOBUFS);
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}
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return (size_t)len;
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}
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size_t
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xsnprintf(char *restrict buf, size_t n, const char *restrict format, ...)
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{
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va_list ap;
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va_start(ap, format);
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size_t len = xvsnprintf(buf, n, format, ap);
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va_end(ap);
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return len;
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}
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