PR#331: for Visual Studio, use a snprintf/vsnprintf wrapper that ensures the string is terminated.

snprintf_compat.h

@@ -0,0 +1,36 @@
+#ifndef __snprintf_compat_h
+#define __snprintf_compat_h
+
+/*
+ * Microsoft's _vsnprintf and _snprint don't always terminate
+ * the string, so use wrappers that ensure that.
+ */
+
+#include <stdarg.h>
+
+#if !defined(HAVE_SNPRINTF) && defined(_MSC_VER)
+static int json_c_vsnprintf(char *str, size_t size, const char *format, va_list ap)
+{
+	int ret;
+	ret = _vsnprintf(str, size, format, ap);
+	str[size - 1] = '\0';
+	return ret;
+}
+#define vsnprintf json_c_vsnprintf
+
+static int json_c_snprintf(char *str, size_t size, const char *format, ...)
+{
+	va_list ap;
+	int ret;
+	va_start(ap, format);
+	ret = json_c_vsnprintf(str, size, format, ap);
+	va_end(ap);
+	return ret;
+}
+#define snprintf json_c_snprintf
+
+#elif !defined(HAVE_SNPRINTF) /* !HAVE_SNPRINTF */
+# error Need vsnprintf!
+#endif /* !HAVE_SNPRINTF && defined(WIN32) */
+
+#endif /* __snprintf_compat_h */