use operator+=(char)

src/bdecode.cpp

@@ -1012,23 +1012,23 @@ done:
 				if (!one_liner) ret += indent_str + 1;
 				for (int i = 0; i < e.list_size(); ++i)
 				{
-					if (i == 0 && one_liner) ret += " ";
+					if (i == 0 && one_liner) ret += ' ';
 					ret += print_entry(e.list_at(i), single_line, indent + 2);
 					if (i < e.list_size() - 1) ret += (one_liner ? ", " : indent_str);
 					else ret += (one_liner ? " " : indent_str + 1);
 				}
-				ret += "]";
+				ret += ']';
 				return ret;
 			}
 			case bdecode_node::dict_t:
 			{
-				ret += "{";
+				ret += '{';
 				bool one_liner = line_longer_than(e, 200) != -1 || single_line;
 
 				if (!one_liner) ret += indent_str + 1;
 				for (int i = 0; i < e.dict_size(); ++i)
 				{
-					if (i == 0 && one_liner) ret += " ";
+					if (i == 0 && one_liner) ret += ' ';
 					std::pair<string_view, bdecode_node> ent = e.dict_at(i);
 					print_string(ret, ent.first, true);
 					ret += ": ";
@@ -1036,7 +1036,7 @@ done:
 					if (i < e.dict_size() - 1) ret += (one_liner ? ", " : indent_str);
 					else ret += (one_liner ? " " : indent_str + 1);
 				}
-				ret += "}";
+				ret += '}';
 				return ret;
 			}
 		}

src/entry.cpp

@@ -644,12 +644,12 @@ namespace {
 	void entry::to_string_impl(std::string& out, int indent) const
 	{
 		TORRENT_ASSERT(indent >= 0);
-		for (int i = 0; i < indent; ++i) out += " ";
+		for (int i = 0; i < indent; ++i) out += ' ';
 		switch (type())
 		{
 		case int_t:
 			out += libtorrent::to_string(integer()).data();
-			out += "\n";
+			out += '\n';
 			break;
 		case string_t:
 			{
@@ -665,12 +665,12 @@ namespace {
 				if (binary_string)
 				{
 					out += aux::to_hex(string());
-					out += "\n";
+					out += '\n';
 				}
 				else
 				{
 					out += string();
-					out += "\n";
+					out += '\n';
 				}
 			} break;
 		case list_t:
@@ -695,16 +695,16 @@ namespace {
 							break;
 						}
 					}
-					for (int j = 0; j < indent + 1; ++j) out += " ";
-					out += "[";
+					for (int j = 0; j < indent + 1; ++j) out += ' ';
+					out += '[';
 					if (binary_string) out += aux::to_hex(i->first);
 					else out += i->first;
-					out += "]";
+					out += ']';
 
 					if (i->second.type() != entry::string_t
 						&& i->second.type() != entry::int_t)
-						out += "\n";
-					else out += " ";
+						out += '\n';
+					else out += ' ';
 					i->second.to_string_impl(out, indent + 2);
 				}
 			} break;

src/error_code.cpp

@@ -288,7 +288,7 @@ namespace libtorrent {
 		{
 			std::string ret;
 			ret += to_string(ev).data();
-			ret += " ";
+			ret += ' ';
 			switch (ev)
 			{
 				case errors::cont: ret += "Continue"; break;

src/lazy_bdecode.cpp

@@ -634,18 +634,18 @@ namespace {
 					if (i < e.list_size() - 1) ret += (one_liner?", ":indent_str);
 					else ret += (one_liner?" ":indent_str+1);
 				}
-				ret += "]";
+				ret += ']';
 				return ret;
 			}
 			case lazy_entry::dict_t:
 			{
-				ret += "{";
+				ret += '{';
 				bool one_liner = line_longer_than(e, 200) != -1 || single_line;
 
 				if (!one_liner) ret += indent_str+1;
 				for (int i = 0; i < e.dict_size(); ++i)
 				{
-					if (i == 0 && one_liner) ret += " ";
+					if (i == 0 && one_liner) ret += ' ';
 					std::pair<std::string, lazy_entry const*> ent = e.dict_at(i);
 					print_string(ret, ent.first.c_str(), int(ent.first.size()), true);
 					ret += ": ";

src/string_util.cpp

@@ -166,7 +166,7 @@ namespace libtorrent {
 		std::string ret;
 		for (auto const& i : in)
 		{
-			if (!ret.empty()) ret += ",";
+			if (!ret.empty()) ret += ',';
 
 #if TORRENT_USE_IPV6
 			error_code ec;
@@ -174,18 +174,18 @@ namespace libtorrent {
 			if (!ec)
 			{
 				// IPv6 addresses must be wrapped in square brackets
-				ret += "[";
+				ret += '[';
 				ret += i.device;
-				ret += "]";
+				ret += ']';
 			}
 			else
 #endif
 			{
 				ret += i.device;
 			}
-			ret += ":";
+			ret += ':';
 			ret += to_string(i.port).data();
-			if (i.ssl) ret += "s";
+			if (i.ssl) ret += 's';
 		}
 
 		return ret;