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Justine Tunney 2020-06-15 07:18:57 -07:00
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libc/mem/vasprintf.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program is distributed in the hope that it will be useful, but │
│ WITHOUT ANY WARRANTY; without even the implied warranty of │
│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/assert.h"
#include "libc/fmt/fmt.h"
#include "libc/mem/mem.h"
/**
* Formats string w/ dynamic memory allocation.
*
* @param *strp is output-only and must be free'd, even on error; since
* that's the behavior that'll make your code most portable
* @return complete bytes written (excluding NUL) or -1 w/ errno
* @see xasprintf() for a better API
*/
int(vasprintf)(char **strp, const char *fmt, va_list va) {
/**
* This implementation guarantees the smallest possible allocation,
* using an optimistic approach w/o changing asymptotic complexity.
*/
size_t size = 32;
if ((*strp = malloc(size))) {
va_list va2;
va_copy(va2, va);
int wrote = (vsnprintf)(*strp, size, fmt, va);
if (wrote == -1) return -1;
if (wrote <= size - 1) {
return wrote;
} else {
size = wrote + 1;
char *buf2 = realloc(*strp, size);
if (buf2) {
*strp = buf2;
wrote = (vsnprintf)(*strp, size, fmt, va2);
assert(wrote == size - 1);
return wrote;
}
}
}
return -1;
}