send: format floating-point numbers with the POSIX locale

Avoid locale-specific number formats (e.g. the comma is used as
decimal separator in some locales).

Closes #142

Author: MaxKellermann

NEWS

@@ -6,6 +6,7 @@ libmpdclient 2.23 (not yet released)
   - new sticker find api
   - new subcommands for "tagtypes": "available", "reset"
 * Support open end for mpd_search_add_window
+* format floating-point numbers with the POSIX localew
 
 libmpdclient 2.22 (2023/12/22)
 * drop the unmaintained Vala bindings

meson.build

@@ -23,6 +23,7 @@ conf.set('DEFAULT_PORT', get_option('default_port'))
 
 conf.set('HAVE_STRNDUP', cc.has_function('strndup', prefix: '#define _GNU_SOURCE\n#include <string.h>'))
 conf.set('HAVE_SETLOCALE', cc.has_function('setlocale', prefix: '#include <locale.h>'))
+conf.set('HAVE_USELOCALE', cc.has_function('uselocale', prefix: '#define _GNU_SOURCE\n#include <locale.h>'))
 
 platform_deps = []
 if host_machine.system() == 'haiku'

src/player.c

@@ -7,10 +7,15 @@
 #include <mpd/response.h>
 #include "isend.h"
 #include "run.h"
+#include "config.h" // for HAVE_USELOCALE
 
 #include <limits.h>
 #include <stdio.h>
 
+#ifdef HAVE_USELOCALE
+#include <locale.h>
+#endif
+
 bool
 mpd_send_current_song(struct mpd_connection *connection)
 {
@@ -196,12 +201,23 @@ bool
 mpd_send_seek_current(struct mpd_connection *connection,
 		      float t, bool relative)
 {
+#ifdef HAVE_USELOCALE
+	// use the POSIX locale to format floating point numbers
+	const locale_t my_locale = newlocale(LC_NUMERIC_MASK, "C", NULL);
+	const locale_t old_locale = uselocale(my_locale);
+#endif
+
 	char ts[32];
 	if (relative)
 		snprintf(ts, sizeof(ts), "%+.3f", (double)t);
 	else
 		snprintf(ts, sizeof(ts), "%.3f", (double)t);
 
+#ifdef HAVE_USELOCALE
+	uselocale(old_locale);
+	freelocale(my_locale);
+#endif
+
 	return mpd_send_command(connection, "seekcur", ts, NULL);
 }
 

src/send.c

@@ -6,11 +6,16 @@
 #include "isend.h"
 #include "internal.h"
 #include "sync.h"
+#include "config.h" // for HAVE_USELOCALE
 
 #include <stdarg.h>
 #include <limits.h>
 #include <stdio.h>
 
+#ifdef HAVE_USELOCALE
+#include <locale.h>
+#endif
+
 /* (bits+1)/3 (plus the sign character) */
 enum {
 	INTLEN = (sizeof(int) * CHAR_BIT + 1) / 3 + 1,
@@ -31,11 +36,22 @@ format_range(char *buffer, size_t size, unsigned start, unsigned end)
 static void
 format_frange(char *buffer, size_t size, float start, float end)
 {
+#ifdef HAVE_USELOCALE
+	// use the POSIX locale to format floating point numbers
+	const locale_t my_locale = newlocale(LC_NUMERIC_MASK, "C", NULL);
+	const locale_t old_locale = uselocale(my_locale);
+#endif
+
 	/* the special value 0.0 means "open range" */
 	if (end >= 0)
 		snprintf(buffer, size, "%1.3f:%1.3f", (double)start, (double)end);
 	else
 		snprintf(buffer, size, "%1.3f:", (double)start);
+
+#ifdef HAVE_USELOCALE
+	uselocale(old_locale);
+	freelocale(my_locale);
+#endif
 }
 
 /**
@@ -153,9 +169,20 @@ bool
 mpd_send_float_command(struct mpd_connection *connection, const char *command,
 		       float arg)
 {
-	char arg_string[FLOATLEN];
+#ifdef HAVE_USELOCALE
+	// use the POSIX locale to format floating point numbers
+	const locale_t my_locale = newlocale(LC_NUMERIC_MASK, "C", NULL);
+	const locale_t old_locale = uselocale(my_locale);
+#endif
 
+	char arg_string[FLOATLEN];
 	snprintf(arg_string, sizeof(arg_string), "%f", (double)arg);
+
+#ifdef HAVE_USELOCALE
+	uselocale(old_locale);
+	freelocale(my_locale);
+#endif
+
 	return mpd_send_command(connection, command, arg_string, NULL);
 }
 
@@ -187,10 +214,22 @@ bool
 mpd_send_u_f_command(struct mpd_connection *connection, const char *command,
 		     unsigned arg1, float arg2)
 {
+#ifdef HAVE_USELOCALE
+	// use the POSIX locale to format floating point numbers
+	const locale_t my_locale = newlocale(LC_NUMERIC_MASK, "C", NULL);
+	const locale_t old_locale = uselocale(my_locale);
+#endif
+
 	char arg1_string[INTLEN], arg2_string[FLOATLEN];
 
 	snprintf(arg1_string, sizeof(arg1_string), "%u", arg1);
 	snprintf(arg2_string, sizeof(arg2_string), "%.3f", (double)arg2);
+
+#ifdef HAVE_USELOCALE
+	uselocale(old_locale);
+	freelocale(my_locale);
+#endif
+
 	return mpd_send_command(connection, command,
 				arg1_string, arg2_string, NULL);
 }