add -Wwrite-strings to CFLAGS if it's available, and fix warnings.

configure.ac

@@ -259,6 +259,12 @@ XMP_TRY_COMPILE(whether compiler understands -Wall,
   int main(){}],
   CFLAGS="${CFLAGS} -Wall")
 
+XMP_TRY_COMPILE(whether compiler understands -Wwrite-strings,
+  ac_cv_c_flag_w_write_strings,
+  -Wwrite-strings,[
+  int main(){}],
+  CFLAGS="${CFLAGS} -Wwrite-strings")
+
 XMP_TRY_COMPILE(whether compiler understands -Wunused-result,
   ac_cv_c_flag_w_unused_result,
   -Wunused-result,[

src/common.h

@@ -19,8 +19,8 @@
 #define MAX_DRV_PARM 20
 
 struct player_mode {
-	char *name;
+	const char *name;
-	char *desc;
+	const char *desc;
 	int mode;
 };
 
@@ -53,8 +53,8 @@ struct options {
 	int show_comment;	/* show module comment text */
 	int player_mode;	/* force tracker emulation */
 	int amiga_mixer;	/* enable amiga mixer */
-	char *driver_id;	/* sound driver ID */
+	const char *driver_id;	/* sound driver ID */
-	char *out_file;		/* output file name */
+	const char *out_file;	/* output file name */
 	char *ins_path;		/* instrument path */
 	char *driver_parm[MAX_DRV_PARM]; /* driver parameters */
 	char mute[XMP_MAX_CHANNELS];
@@ -82,7 +82,7 @@ void delay_ms(int msec);
 /* option */
 void get_options(int, char **, struct options *);
 int read_config(struct options *);
-void read_modconf(struct options *, unsigned char *);
+void read_modconf(struct options *, const unsigned char *);
 
 /* terminal */
 int set_tty(void);

src/getopt_long.c

@@ -75,7 +75,7 @@ char   *optarg = NULL;		/* argument associated with option */
 #define	BADARG		((*options == ':') ? (int)':' : (int)'?')
 #define	INORDER 	(int)1
 
-#define	EMSG		""
+static char EMSG[] = {0,0,0,0}; /* #define EMSG "" */
 
 static int getopt_internal(int, char * const *, const char *,
 			   const struct option *, int *, int);

src/main.c

@@ -178,13 +178,13 @@ static void check_pause(xmp_context xc, struct control *ctl,
 
 static void get_mixer_type(int t, struct options *opt, char *buf, size_t size)
 {
-	char *fmt;
+	const char *fmt;
 
 	fmt = opt->format & XMP_FORMAT_MONO ? "mono" : "stereo";
 
 	switch (t) {
 	case XMP_MIXER_STANDARD: {
-		char *itp;
+		const char *itp;
 		switch (opt->interp) {
 		case XMP_INTERP_NEAREST:
 			itp = "non-interpolated";
@@ -211,9 +211,9 @@ static void get_mixer_type(int t, struct options *opt, char *buf, size_t size)
 	}
 }
 
-static void load_error(char *name, char *filename, int val)
+static void load_error(const char *name, const char *filename, int val)
 {
-	char *msg;
+	const char *msg;
 
 	val = -val;
 	switch (val) {

src/read_config.c

@@ -174,7 +174,7 @@ int read_config(struct options *o)
 }
 
 
-static int compare_md5(unsigned char *d, char *digest)
+static int compare_md5(const unsigned char *d, const char *digest)
 {
 	int i;
 
@@ -191,7 +191,7 @@ static int compare_md5(unsigned char *d, char *digest)
 	return 0;
 }
 
-static void parse_modconf(struct options *o, char *confname, unsigned char *md5)
+static void parse_modconf(struct options *o, const char *confname, const unsigned char *md5)
 {
 	FILE *rc;
 	char *hash, *var, *val, line[256];
@@ -281,7 +281,7 @@ static void parse_modconf(struct options *o, char *confname, unsigned char *md5)
 }
 
 
-void read_modconf(struct options *o, unsigned char *md5)
+void read_modconf(struct options *o, const unsigned char *md5)
 {
 #if defined(__OS2__) || defined(__EMX__)
 	char myrc[PATH_MAX];

src/sound.c

@@ -102,7 +102,7 @@ struct sound_driver *select_sound_driver(struct options *options)
 {
 	struct list_head *head;
 	struct sound_driver *sd;
-	char *pref = options->driver_id;
+	const char *pref = options->driver_id;
 
 	if (pref) {
 		list_for_each(head, &sound_driver_list) {

src/sound.h

@@ -8,7 +8,7 @@
 
 struct sound_driver {
 	const char *id;
-	char *description;
+	const char *description;
 	const char *const *help;
 	int (*init)(struct options *);
 	void (*deinit)(void);

src/sound_file.c

@@ -75,7 +75,7 @@ static void play(void *b, int len)
 
 static void deinit(void)
 {
-	free(sound_file.description);
+	free((void *)sound_file.description);
 }
 
 static void flush(void)
@@ -107,4 +107,3 @@ struct sound_driver sound_file = {
 	onpause,
 	onresume
 };
-

src/sound_wav.c

@@ -148,7 +148,7 @@ static void deinit(void)
 		close(fd);
 	}
 
-	free(sound_wav.description);
+	free((void *)sound_wav.description);
 }
 
 static void flush(void)
@@ -175,4 +175,3 @@ struct sound_driver sound_wav = {
 	onpause,
 	onresume
 };
-