error: Implement the error function

This follows the exceptionally-detailed functional description in the
manual page.

Signed-off-by: Samuel Holland <samuel@sholland.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/libgcompat/error.c b/libgcompat/error.c
new file mode 100644
index 0000000..c759b19
--- /dev/null
+++ b/libgcompat/error.c
@@ -0,0 +1,27 @@
+#define _GNU_SOURCE /* program_invocation_name */
+#include <errno.h>  /* program_invocation_name */
+#include <stdarg.h> /* va_list, va_start, va_end */
+#include <stdio.h>  /* fflush, fputc, fputs, stderr, stdout, vfprintf */
+#include <string.h> /* strerror */
+
+/**
+ * Print an error message.
+ *
+ * LSB 5.0: LSB-Core-generic/baselib-error-n.html
+ */
+void error(int status, int errnum, const char *format, ...)
+{
+	va_list ap;
+
+	fflush(stdout);
+	fputs(program_invocation_name, stderr);
+	fputs(": ", stderr);
+	va_start(ap, format);
+	vfprintf(stderr, format, ap);
+	va_end(ap);
+	if (errnum != 0) {
+		fputs(": ", stderr);
+		fputs(strerror(errnum), stderr);
+		fputc('\n', stderr);
+	}
+}