strbuf: add xstrfmt helper

You can use a strbuf to build up a string from parts, and
then detach it. In the general case, you might use multiple
strbuf_add* functions to do the building. However, in many
cases, a single strbuf_addf is sufficient, and we end up
with:

  struct strbuf buf = STRBUF_INIT;
  ...
  strbuf_addf(&buf, fmt, some, args);
  str = strbuf_detach(&buf, NULL);

We can make this much more readable (and avoid introducing
an extra variable, which can clutter the code) by
introducing a convenience function:

  str = xstrfmt(fmt, some, args);

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/strbuf.h b/strbuf.h
index e9ad03e..a594c24 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -187,4 +187,13 @@ extern int fprintf_ln(FILE *fp, const char *fmt, ...);
 
 char *xstrdup_tolower(const char *);
 
+/*
+ * Create a newly allocated string using printf format. You can do this easily
+ * with a strbuf, but this provides a shortcut to save a few lines.
+ */
+__attribute__((format (printf, 1, 0)))
+char *xstrvfmt(const char *fmt, va_list ap);
+__attribute__((format (printf, 1, 2)))
+char *xstrfmt(const char *fmt, ...);
+
 #endif /* STRBUF_H */