I need to calculate the size need for formated wchar array.
Consider following code:
wchar_t* Format(const wchar_t* format, ...)
{
va_list args;
va_start(args, format);
wchar_t *w = NULL;
int len = _vsnwprintf(NULL, 0, format, args) + 1; // <------ Error
if (len > 0)
{
w = new wchar_t[len];
w[0] = 0;
_vsnwprintf_s(w, len, len, format, args);
}
va_end(args);
return w;
}
if _CRT_SECURE_NO_WARNINGS
is turned on, above code work, if not, the error say:
'_vsnwprintf': This function or variable may be unsafe. Consider using _vsnwprintf_s instead.
But I can not manage to use _vsnwprintf_s
to calculate the size needed for the wchar buffer.
Following is what I tried:
int len = _vsnwprintf_s(NULL, 0, 0, format, args); // return 1
// debug assertion failed: string != NULL && DstSizeInWords > 0
int len = _vsnwprintf_s(NULL, 0, INT_MAX, format, args);
// debug assertion failed: string != NULL && DstSizeInWords > 0
int len = _vsnwprintf_s(NULL, INT_MAX, 0, format, args);
// debug assertion failed: string != NULL && DstSizeInWords > 0
int len = _vsnwprintf_s(NULL, INT_MAX, INT_MAX, format, args);
Other function: _snwprintf
give _CRT_SECURE
error and _snwprintf_s
have same effect with _vsnwprintf_s
Although I pretty okay with _CRT_SECURE_NO_WARNINGS
turned on, I wonder how can I calculate the size needed for formated wchar array, CRT_SECURE
way? Note that it must accept va_list
as agrument.
You should be able to obtain required buffer size using _vscwprintf
:
_Check_return_ _Ret_z_ wchar_t *
Format(_Printf_format_string_ _In_z_ wchar_t const * const psz_format, ...)
{
size_t formatted_string_length;
va_list args;
{
va_start(args, psz_format);
int const result(::_vscwprintf(psz_format, args));
va_end(args);
if(-1 == result)
{
::abort();
}
assert(0 <= result);
formatted_string_length = static_cast< size_t >(result);
}
size_t const buffer_size(formatted_string_length + 1u);
wchar_t * const p_buffer(new wchar_t[buffer_size]);
{
va_start(args, psz_format);
int const result(::_vsnwprintf_s(p_buffer, buffer_size, formatted_string_length, psz_format, args));
va_end(args);
if(-1 == result)
{
::abort();
}
assert(0 <= result);
assert(static_cast< size_t >(result) == formatted_string_length);
assert(L'\0' == p_buffer[formatted_string_length]);
}
return p_buffer;
}