1497 int os::log_vsnprintf(char* buf, size_t len, const char* fmt, va_list args) {

  1497 int os::vsnprintf(char* buf, size_t len, const char* fmt, va_list args) {

  1498   int ret = vsnprintf(buf, len, fmt, args);

  1498 #if _MSC_VER >= 1900

  1499   // Get the correct buffer size if buf is too small

  1499   // Starting with Visual Studio 2015, vsnprint is C99 compliant.

  1500   if (ret < 0) {

  1500   int result = ::vsnprintf(buf, len, fmt, args);

  1501     return _vscprintf(fmt, args);

  1501   // If an encoding error occurred (result < 0) then it's not clear

  1502   }

  1502   // whether the buffer is NUL terminated, so ensure it is.

  1503   return ret;

  1503   if ((result < 0) && (len > 0)) {

  1504     buf[len - 1] = '\0';

  1505   }

  1506   return result;

  1507 #else

  1508   // Before Visual Studio 2015, vsnprintf is not C99 compliant, so use

  1509   // _vsnprintf, whose behavior seems to be *mostly* consistent across

  1510   // versions.  However, when len == 0, avoid _vsnprintf too, and just

  1511   // go straight to _vscprintf.  The output is going to be truncated in

  1512   // that case, except in the unusual case of empty output.  More

  1513   // importantly, the documentation for various versions of Visual Studio

  1514   // are inconsistent about the behavior of _vsnprintf when len == 0,

  1515   // including it possibly being an error.

  1516   int result = -1;

  1517   if (len > 0) {

  1518     result = _vsnprintf(buf, len, fmt, args);

  1519     // If output (including NUL terminator) is truncated, the buffer

  1520     // won't be NUL terminated.  Add the trailing NUL specified by C99.

  1521     if ((result < 0) || (result >= len)) {

  1522       buf[len - 1] = '\0';

  1523     }

  1524   }

  1525   if (result < 0) {

  1526     result = _vscprintf(fmt, args);

  1527   }

  1528   return result;

  1529 #endif // _MSC_VER dispatch