Add usage()

3 files changed, 31 insertions, 1 deletions

diff --git a/README b/README
index 51585b3..0df0068 100644
--- a/README
+++ b/README
@@ -77,6 +77,7 @@ FEATURES:
         • Functions for getting and setting the program name
         • Functions for printing diagnostics and optionally crashing with
           strerror() support
+        • Generate usage strings
     • macros.h
         • MIN()/MAX()/CLAMP()
         • Better assertion macro
@@ -112,7 +113,7 @@ FEATURES:
 
 PLANNED FEATURES:
 
-    • String Case Conversions         (unicode/string.h)
+    • Titlecase Conversions           (unicode/string.h)
     • Unicode Normalization           (unicode/string.h)
     • Line- and Sentence Segmentation (unicode/string.h)
 
diff --git a/include/errors.h b/include/errors.h
index 961ecf1..c8576f0 100644
--- a/include/errors.h
+++ b/include/errors.h
@@ -5,6 +5,9 @@
 
 #include "_attrs.h"
 
+void usage(const char *, ...);
+#define usage(...) usage(__VA_ARGS__, nullptr)
+
 [[gnu::format(printf, 1, 2)]] void warn(const char *, ...);
 void vwarn(const char *, va_list);
 
diff --git a/lib/errors/usage.c b/lib/errors/usage.c
new file mode 100644
index 0000000..50ca04f
--- /dev/null
+++ b/lib/errors/usage.c
@@ -0,0 +1,26 @@
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "errors.h"
+#include "macros.h"
+
+void
+(usage)(const char *s, ...)
+{
+	ASSUME(s != nullptr);
+	ASSUME(mlib_progname() != nullptr);
+
+	va_list ap;
+	va_start(ap, s);
+
+	fprintf(stderr, "Usage: %s %s\n", mlib_progname(), s);
+
+	while ((s = va_arg(ap, char *)) != nullptr) {
+		for (size_t i = 0; i < lengthof("Usage: ") - 1; i++)
+			fputc(' ', stderr);
+		fprintf(stderr, "%s %s\n", mlib_progname(), s);
+	}
+
+	va_end(ap);
+}