From mboxrd@z Thu Jan  1 00:00:00 1970
From: Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH/RFC 02/11] strbuf: add non-variadic function
 strbuf_vaddf()
Date: Wed, 25 Nov 2009 16:59:24 -0800
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Cc: msysgit@googlegroups.com, git@vger.kernel.org,
	dotzenlabs@gmail.com, Erik Faye-Lund <kusmabite@gmail.com>
To: Erik Faye-Lund <kusmabite@googlemail.com>
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In-Reply-To: <1259196260-3064-3-git-send-email-kusmabite@gmail.com> (Erik
 Faye-Lund's message of "Thu\, 26 Nov 2009 00\:44\:11 +0000")
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Erik Faye-Lund <kusmabite@googlemail.com> writes:

> +void strbuf_vaddf(struct strbuf *sb, const char *fmt, va_list ap)
>  {
>  	int len;
>  
>  	if (!strbuf_avail(sb))
>  		strbuf_grow(sb, 64);
>  	len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);
>  	if (len < 0)
>  		die("your vsnprintf is broken");
>  	if (len > strbuf_avail(sb)) {
>  		strbuf_grow(sb, len);
>  		len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);
>  		if (len > strbuf_avail(sb)) {
>  			die("this should not happen, your snprintf is broken");
>  		}

Hmm, I would have expected to see va_copy() somewhere in the patch text.
Is it safe to reuse ap like this in two separate invocations of
vsnprintf()?