在 2026-6-24 15:35, Yonggang Luo 写道:
## ProblemAfter commit c85d64d8c ("crt: Add support for C95 (v)swprintf() functions when __USE_MINGW_ANSI_STDIO=1"), swprintf(buf, n, ...) returns -1 when the formatted output exactly fills n - 1 wide characters (plus the terminator), even though ISO C95+ requires -1 only when n or more data wide characters are needed.
diff --git a/mingw-w64-crt/testcases/t_swprintf_tmpl.h
b/mingw-w64-crt/testcases/t_swprintf_tmpl.h
index a12cba9a2..5fe332645 100644
--- a/mingw-w64-crt/testcases/t_swprintf_tmpl.h
+++ b/mingw-w64-crt/testcases/t_swprintf_tmpl.h
@@ -19,5 +19,23 @@ int main() {
fprintf(stderr, "\n");
return 1;
}
+
+ /* ISO C95+: output of 9 wide chars plus terminator must succeed when n=10.
+ * Regression for __mingw_vswprintf exact-fit check (retval == n-1). */
+ {
+ wchar_t exact[16] = L"XXXXXXXXXXXXXXXX";
While initializing an array without a null terminator this way is perfectly fine in standard C, GCC can warn about it:
warning: initializer-string for array of 'short unsigned int' truncates NUL terminator but destination lacks 'nonstring' attribute (34 chars into 32 available) [-Wunterminated-string-initialization]
12 | wchar_t exact[16] = L"XXXXXXXXXXXXXXXX";
| ^~~~~~~~~~~~~~~~~~~
So I have to delete one X from the initializer.
The other change looks good. Fixed and pushed now. Thanks.
--
Best regards,
LIU Hao
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