*: add explicit

src/output/plugins/AoOutputPlugin.cxx

@@ -52,7 +52,7 @@ class AoOutput final : AudioOutput, SafeSingleton<AoInit> {
 
 	size_t frame_size;
 
-	AoOutput(const ConfigBlock &block);
+	explicit AoOutput(const ConfigBlock &block);
 	~AoOutput() override;
 
 public:

src/output/plugins/FifoOutputPlugin.cxx

@@ -42,7 +42,7 @@ class FifoOutput final : AudioOutput {
 	Timer *timer;
 
 public:
-	FifoOutput(const ConfigBlock &block);
+	explicit FifoOutput(const ConfigBlock &block);
 
 	~FifoOutput() override {
 		CloseFifo();

src/output/plugins/NullOutputPlugin.cxx

@@ -27,7 +27,7 @@ class NullOutput final  : AudioOutput {
 	Timer *timer;
 
 public:
-	NullOutput(const ConfigBlock &block)
+	explicit NullOutput(const ConfigBlock &block)
 		:AudioOutput(0),
 		 sync(block.GetBlockValue("sync", true)) {}
 

src/output/plugins/OpenALOutputPlugin.cxx

@@ -44,7 +44,7 @@ class OpenALOutput final : AudioOutput {
 	ALenum format;
 	ALuint frequency;
 
-	OpenALOutput(const ConfigBlock &block);
+	explicit OpenALOutput(const ConfigBlock &block);
 
 public:
 	static AudioOutput *Create(EventLoop &,

src/output/plugins/PipeOutputPlugin.cxx

@@ -30,7 +30,7 @@ class PipeOutput final : AudioOutput {
 	const std::string cmd;
 	FILE *fh;
 
-	PipeOutput(const ConfigBlock &block);
+	explicit PipeOutput(const ConfigBlock &block);
 
 public:
 	static AudioOutput *Create(EventLoop &,

src/output/plugins/RecorderOutputPlugin.cxx

@@ -67,7 +67,7 @@ class RecorderOutput final : AudioOutput {
 	 */
 	FileOutputStream *file;
 
-	RecorderOutput(const ConfigBlock &block);
+	explicit RecorderOutput(const ConfigBlock &block);
 
 public:
 	static AudioOutput *Create(EventLoop &, const ConfigBlock &block) {