win32: implement vsnprintf(2)

The Microsoft C runtime may include a defective version of vsnprintf.
Implement a standards-compliant replacement.

1 files changed, 21 insertions, 0 deletions

diff --git a/win32/winansi.c b/win32/winansi.c
index 167b4b0b1..9e7d10a56 100644
--- a/win32/winansi.c
+++ b/win32/winansi.c
@@ -552,6 +552,27 @@ int winansi_fputs(const char *str, FILE *stream)
         return ansi_emulate(str, stream) == EOF ? EOF : 0;
 }
 
+#if !defined(__USE_MINGW_ANSI_STDIO) || !__USE_MINGW_ANSI_STDIO
+/*
+ * Prior to Windows 10 vsnprintf was incompatible with the C99 standard.
+ * Implement a replacement using _vsnprintf.
+ */
+int winansi_vsnprintf(char *buf, size_t size, const char *format, va_list list)
+{
+        size_t len;
+        va_list list2;
+
+        va_copy(list2, list);
+        len = _vsnprintf(NULL, 0, format, list2);
+        if (len < 0)
+                return -1;
+
+        _vsnprintf(buf, size, format, list);
+        buf[size-1] = '\0';
+        return len;
+}
+#endif
+
 int winansi_vfprintf(FILE *stream, const char *format, va_list list)
 {
         int len, rv;