win32: implement vsnprintf(2)

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

2 files changed, 25 insertions, 0 deletions

diff --git a/include/mingw.h b/include/mingw.h
index 2dc3ddfd7..f9c098917 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -134,6 +134,7 @@ int winansi_putchar(int c);
 int winansi_puts(const char *s);
 size_t winansi_fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);
 int winansi_fputs(const char *str, FILE *stream);
+int winansi_vsnprintf(char *buf, size_t size, const char *format, va_list list);
 int winansi_vfprintf(FILE *stream, const char *format, va_list list);
 int winansi_printf(const char *format, ...) __attribute__((format (printf, 1, 2)));
 int winansi_fprintf(FILE *stream, const char *format, ...) __attribute__((format (printf, 2, 3)));
@@ -144,6 +145,9 @@ int winansi_getc(FILE *stream);
 #define puts winansi_puts
 #define fwrite winansi_fwrite
 #define fputs winansi_fputs
+#if !defined(__USE_MINGW_ANSI_STDIO) || !__USE_MINGW_ANSI_STDIO
+#define vsnprintf(buf, size, ...) winansi_vsnprintf(buf, size,  __VA_ARGS__)
+#endif
 #define vfprintf(stream, ...) winansi_vfprintf(stream, __VA_ARGS__)
 #define vprintf(...) winansi_vfprintf(stdout, __VA_ARGS__)
 #define printf(...) winansi_printf(__VA_ARGS__)
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;