1 files changed, 56 insertions, 0 deletions
diff --git a/vweprintf.c b/vweprintf.c
new file mode 100644
index 0000000..605f1c2
--- /dev/null
+++ b/vweprintf.c
@@ -0,0 +1,56 @@
+/* See LICENSE file for copyright and license details. */
+#include "libsimple.h"
+
+
+extern char *argv0;
+
+
+void
+vweprintf(const char *fmt, va_list ap)
+{
+	int saved_errno = errno, r;
+	const char *end = strchr(fmt, '\0');
+	const char *prefix1 = argv0;
+	const char *prefix2 = ": ";
+	const char *suffix1 = "";
+	const char *suffix2 = "";
+	const char *suffix3 = "";
+	char *message = NULL;
+	va_list ap1;
+	va_list ap2;
+
+	if (!argv0 || !strncmp(fmt, "usage: ", strlen("usage: ")))
+		prefix1 = prefix2 = "";
+
+	va_copy(ap1, ap);
+	va_copy(ap2, ap);
+	r = vsnprintf(NULL, 0, fmt, ap1);
+	if (0 <= r && (size_t)r < SIZE_MAX) {
+		message = alloca((size_t)r + 1);
+		vsprintf(message, fmt, ap2);
+	}
+	va_end(ap2);
+	va_end(ap1);
+
+	if (!*fmt) {
+		suffix1 = strerror(saved_errno);
+		suffix2 = "\n";
+	} else if (end[-1] == ':') {
+		suffix1 = " ";
+		suffix2 = strerror(saved_errno);
+		suffix3 = "\n";
+	} else if (end[-1] != '\n') {
+		suffix1 = "\n";
+	}
+
+	if (message) {
+		/* This is to avoid mangling when multiple processes are writting. */
+		fprintf(stderr, "%s%s%s%s%s%s", prefix1, prefix2, message, suffix1, suffix2, suffix3);
+	} else {
+		fprintf(stderr, "%s%s", prefix1, prefix2);
+		vfprintf(stderr, fmt, ap);
+		fprintf(stderr, "%s%s%s", suffix1, suffix2, suffix3);
+	}
+
+	errno = saved_errno;
+}