Refactor join function

src/clib/lib/job_queue/slurm_driver.cpp

@@ -161,26 +161,26 @@ static std::string load_stdout(const char *cmd,
 
 static std::vector<std::string> split_string(const std::string &string_value) {
     std::vector<std::string> strings;
+
     std::size_t offset = string_value.find_first_not_of(", ");
     while (offset != std::string::npos) {
         auto item_end = string_value.find_first_of(", ", offset);
         strings.push_back(string_value.substr(offset, item_end - offset));
         offset = string_value.find_first_not_of(", ", item_end);
     }
+
     return strings;
 }
 
 template <typename C> static std::string join_string(const C &strings) {
-    const std::string sep = ",";
-    std::string full_string;
-    bool first = true;
-    for (const auto &s : strings) {
-        if (!first)
-            full_string += sep;
-        full_string += s;
-        first = false;
+    std::string str;
+
+    for (const auto &key : strings) {
+        str.append(",");
+        str.append(key);
     }
-    return full_string;
+
+    return str.substr(str.find_first_not_of(','));
 }
 
 void *slurm_driver_alloc() {