Re: [PATCH] Use open_memstream(3) for more efficient asprintf

[Alex Brachet-Mialot <alexbrachetmialot@gmail.com>]

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That's strange, I looked on the archives and it looks like my
attachment was in a weird format, something my email client did
perhaps. Here it is copied I'll also try again with .txt extension so
my mail client is less confused hopefully. Sorry about that.

diff --git a/src/stdio/vasprintf.c b/src/stdio/vasprintf.c
index 08251bc2..d55fe32f 100644
--- a/src/stdio/vasprintf.c
+++ b/src/stdio/vasprintf.c
@@ -5,11 +5,16 @@

 int vasprintf(char **s, const char *fmt, va_list ap)
 {
-    va_list ap2;
-    va_copy(ap2, ap);
-    int l = vsnprintf(0, 0, fmt, ap2);
-    va_end(ap2);
+    size_t l;
+    *s = 0;
+    FILE *f = open_memstream(s, &l);
+    if (!f)
+        return -1;

-    if (l<0 || !(*s=malloc(l+1U))) return -1;
-    return vsnprintf(*s, l+1U, fmt, ap);
+    if ((l = vfprintf(f, fmt, ap)) == -1) {
+        free(*s);
+        *s = 0;
+    }
+    fclose(f);
+    return l;
 }


On Mon, Oct 14, 2019 at 2:48 AM Alex Brachet-Mialot
<alexbrachetmialot@gmail.com> wrote:
>
> Hi I wasn't able to search the lists from the online archive, so I'm not sure if it has been talked about yet, but the current vasprintf implementation could be made better if it didn't call vsnprintf twice. Let me know what you think!

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diff --git a/src/stdio/vasprintf.c b/src/stdio/vasprintf.c
index 08251bc2..d55fe32f 100644
--- a/src/stdio/vasprintf.c
+++ b/src/stdio/vasprintf.c
@@ -5,11 +5,16 @@
 
 int vasprintf(char **s, const char *fmt, va_list ap)
 {
-	va_list ap2;
-	va_copy(ap2, ap);
-	int l = vsnprintf(0, 0, fmt, ap2);
-	va_end(ap2);
+	size_t l;
+	*s = 0;
+	FILE *f = open_memstream(s, &l);
+	if (!f)
+		return -1;
 
-	if (l<0 || !(*s=malloc(l+1U))) return -1;
-	return vsnprintf(*s, l+1U, fmt, ap);
+	if ((l = vfprintf(f, fmt, ap)) == -1) {
+		free(*s);
+		*s = 0;
+	}
+	fclose(f);
+	return l;
 }