Improve argv_to_string_alloc()

1. Fix bug in argv_to_string_alloc(),
   which did not increase buffer size to account for number of separators.

2. Improve coding
   a. Initialize buffer size to one to account for terminator,
      which avoids the need to later increment by one.
   b. Call concat_argv() directly, instead of calling argv_to_string(),
      which is a wrapper.

3. Add similar function argv_to_string_alloc_prefix(),
   which preloads string buffer with a prefix string.

include/tig/argv.h

@@ -24,6 +24,7 @@
 #define DIFF_ARGS "%(diffargs)"
 
 bool argv_to_string(const char *argv[], char *buf, size_t buflen, const char *sep);
+char *argv_to_string_alloc_prefix(const char *argv[], const char *sep, const char *prefix);
 char *argv_to_string_alloc(const char *argv[], const char *sep);
 bool argv_to_string_quoted(const char *argv[SIZEOF_ARG], char *buf, size_t buflen, const char *sep);
 bool argv_from_string_no_quotes(const char *argv[SIZEOF_ARG], int *argc, char *cmd);

src/argv.c

@@ -56,16 +56,43 @@ concat_argv(const char *argv[], char *buf, size_t buflen, const char *sep, bool
 }
 
 char *
-argv_to_string_alloc(const char *argv[], const char *sep)
+argv_to_string_alloc_prefix(const char *argv[], const char *sep, const char *prefix)
 {
-	size_t i, size = 0;
-	char *buf;
+	size_t i, size = 1;
+	for (i = 0; argv[i]; i++)
+		size += strlen(argv[i]);
+
+	/* Increase buffer size by separator size and number of separators */
+	if (sep) if (i) size += strlen(sep) * (i - 1);
+
+	/* Increase buffer size by prefix size */
+	if (prefix) size += strlen(prefix);
+
+	char *buf = malloc(size);
+	if (buf) {
+
+		/* Preload buffer with prefix */
+		for (i = 0; prefix[i]; i++) buf[i] = prefix[i];
+
+		/* Load buffer after prefix with concatenated version of argv */
+		if (concat_argv(argv, buf + i, size, sep, false)) return buf;
+	}
+	free(buf);
+	return NULL;
+}
 
+char *
+argv_to_string_alloc(const char *argv[], const char *sep)
+{
+	size_t i, size = 1;
 	for (i = 0; argv[i]; i++)
 		size += strlen(argv[i]);
 
-	buf = malloc(size + 1);
-	if (buf && argv_to_string(argv, buf, size + 1, sep))
+	/* Increase buffer size by separator size and number of separators */
+	if (sep) if (i) size += strlen(sep) * (i - 1);
+
+	char *buf = malloc(size);
+	if (buf && concat_argv(argv, buf, size, sep, false))
 		return buf;
 	free(buf);
 	return NULL;