When preparing an error message in a strbuf, it can be convenient
to add a formatted string to the beginning:
if (transaction_commit(&t, err)) {
strbuf_prefixf(err, "cannot fetch '%s': ", remotename);
return -1;
}
The new strbuf_prefixf is like strbuf_addf, except it writes its
result to the beginning of a strbuf instead of the end.
The current implementation uses strlen(strfmt(fmt, ...)) extra bytes
at the end of the strbuf as temporary scratch space for convenience
and simplicity. A later patch can optimize if needed.
Signed-off-by: Jonathan Nieder <jrnieder@xxxxxxxxx>
---
strbuf.c | 16 ++++++++++++++++
strbuf.h | 4 ++++
2 files changed, 20 insertions(+)
diff --git a/strbuf.c b/strbuf.c
index 0346e74..3f4aaa3 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -219,6 +219,22 @@ void strbuf_addf(struct strbuf *sb, const char *fmt, ...)
va_end(ap);
}
+void strbuf_prefixf(struct strbuf *sb, const char *fmt, ...)
+{
+ va_list ap;
+ size_t pos, len;
+
+ pos = sb->len;
+
+ va_start(ap, fmt);
+ strbuf_vaddf(sb, fmt, ap);
+ va_end(ap);
+
+ len = sb->len - pos;
+ strbuf_insert(sb, 0, sb->buf + pos, len);
+ strbuf_remove(sb, pos + len, len);
+}
+
static void add_lines(struct strbuf *out,
const char *prefix1,
const char *prefix2,
diff --git a/strbuf.h b/strbuf.h
index 652b6c4..5dae48e 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -158,6 +158,10 @@ extern void strbuf_vaddf(struct strbuf *sb, const char *fmt, va_list ap);
extern void strbuf_add_lines(struct strbuf *sb, const char *prefix, const char *buf, size_t size);
+/* Like strbuf_addf but insert at the front of sb instead of appending. */
+__attribute__((format (printf,2,3)))
+extern void strbuf_prefixf(struct strbuf *sb, const char *fmt, ...);
+
/*
* Append s to sb, with the characters '<', '>', '&' and '"' converted
* into XML entities.
--
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