Add helper function to extend C strings

This is trivial to do with Qt, but when we want to be able to do this in C
code it takes a little more work. This creates a simple pattern to extend
an existing C string.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

2 files changed, 31 insertions, 0 deletions

diff --git a/membuffer.c b/membuffer.c
index c8a06662f..c7d2bbdd2 100644
--- a/membuffer.c
+++ b/membuffer.c
@@ -228,3 +228,32 @@ void put_quoted(struct membuffer *b, const char *text, int is_attribute, int is_
 		text = p;
 	}
 }
+
+char *add_to_string_va(const char *old, const char *fmt, va_list args)
+{
+	char *res;
+	struct membuffer o = { 0 }, n = { 0 };
+	put_vformat(&n, fmt, args);
+	put_format(&o, "%s\n%s", old ?: "", mb_cstring(&n));
+	res = strdup(mb_cstring(&o));
+	free_buffer(&o);
+	free_buffer(&n);
+	free((void *)old);
+	return res;
+}
+
+/* this is a convenience function that cleverly adds text to a string, using our membuffer
+ * infrastructure.
+ * WARNING - this will free(old), the intended pattern is
+ * string = add_to_string(string, fmt, ...)
+ */
+char *add_to_string(const char *old, const char *fmt, ...)
+{
+	char *res;
+	va_list args;
+
+	va_start(args, fmt);
+	res = add_to_string_va(old, fmt, args);
+	va_end(args);
+	return res;
+}
diff --git a/membuffer.h b/membuffer.h
index 153815fd8..c0a4f6029 100644
--- a/membuffer.h
+++ b/membuffer.h
@@ -27,6 +27,8 @@ extern void strip_mb(struct membuffer *);
 extern const char *mb_cstring(struct membuffer *);
 extern __printf(2, 0) void put_vformat(struct membuffer *, const char *, va_list);
 extern __printf(2, 3) void put_format(struct membuffer *, const char *fmt, ...);
+extern __printf(2, 0) char *add_to_string_va(const char *old, const char *fmt, va_list args);
+extern __printf(2, 3) char *add_to_string(const char *old, const char *fmt, ...);
 
 /* Output one of our "milli" values with type and pre/post data */
 extern void put_milli(struct membuffer *, const char *, int, const char *);