I have a VC++ 6.0 project which I am now compiling using VS2008 . I have this piece of code that used to compile under VC++ 6 but throws an error under VS2008 :
int CIDStorage::Length()
{
CIDStorage* m_ptr = this;
for(int i = 0;m_ptr->m_ptrNext != NULL;i++)
m_ptr = m_ptr->m_ptrNext;
if(i == 0)
if(m_ID.IsEmpty())
return 0;
return i+1;
}
the error is 'i' : undeclared identifier
No probs with that I can see how that came about . So ... Do I change the source code . Or is there a compiler setting I could set that cures this ?
VC++ 6 (normally1) follows a pre-standard rule where a variable defined in a for loop remains defined for the rest of the scope in which that for loop resides. VC++ 2008 follows the standard rule where the for loop defines a new scope, and the variable is defined only within that scope.
The cure is pretty simple -- define the variable outside the loop:
int CIDStorage::Length()
{
CIDStorage* m_ptr = this;
int i;
for(i = 0; m_ptr->m_ptrNext != NULL; i++)
m_ptr = m_ptr->m_ptrNext;
if(i == 0)
if(m_ID.IsEmpty())
return 0;
return i+1;
}
1 The compiler in VC++ is actually capable of following the correct rules for scoping of variables defined in a for loop. Unfortunately, to follow the rule, you have to use the /Za flag, which tries to enforce all the rules it knows as strictly as possible. That turns out to be completely unusable because with that turned on, it rejects (virtually?) all of its own headers as containing errors!
Related
I have some issues with the CMonthCalCtrl control and modernizing my code. The first problem is related to the BOLDDAY macro.
This macro is used to adjust day states (making specific dates bold on the calendar) and the concept is described in detail here. As documented, you need to define a macro:
#define BOLDDAY(ds, iDay) if(iDay > 0 && iDay < 32) \
(ds) |= (0x00000001 << (iDay-1))
Here is my code that uses this macro so that you have some context:
void CMeetingScheduleAssistantDlg::InitDayStateArray(int iMonthCount, LPMONTHDAYSTATE pDayState, COleDateTime datStart)
{
int iMonth = 0;
COleDateTimeSpan spnDay;
CString strKey;
SPECIAL_EVENT_S *psEvent = nullptr;
if (pDayState == nullptr)
return;
memset(pDayState, 0, sizeof(MONTHDAYSTATE)*iMonthCount);
if (m_pMapSPtrEvents == nullptr && m_Reminders.Count() == 0)
{
return;
}
spnDay.SetDateTimeSpan(1, 0, 0, 0);
auto datDay = datStart;
const auto iStartMonth = datStart.GetMonth();
auto iThisMonth = iStartMonth;
auto iLastMonth = iThisMonth;
do
{
strKey = datDay.Format(_T("%Y-%m-%d"));
if (m_pMapSPtrEvents != nullptr)
{
psEvent = nullptr;
m_pMapSPtrEvents->Lookup(strKey, reinterpret_cast<void*&>(psEvent));
if (psEvent != nullptr)
{
BOLDDAY(pDayState[iMonth], datDay.GetDay());
}
}
if (m_Reminders.HasReminder(datDay))
{
BOLDDAY(pDayState[iMonth], datDay.GetDay());
}
datDay = datDay + spnDay;
iThisMonth = datDay.GetMonth();
if (iThisMonth != iLastMonth)
{
iLastMonth = iThisMonth;
iMonth++;
}
} while (iMonth < iMonthCount);
}
Everywhere I use this BOLDDAY macro I get a code analysis warning (C26481):
warning C26481: Don't use pointer arithmetic. Use span instead (bounds.1).
It is not clear to me if the problem is with the BOLDDAY macro or my own code?
Update
I still get the warning when I turn the macro into a function:
Update 2
If it helps, I currently call the InitDayStateArray function in the following ways:
Method 1:
void CMeetingScheduleAssistantDlg::SetDayStates(CMonthCalCtrl &rCalendar)
{
COleDateTime datFrom, datUntil;
const auto iMonthCount = rCalendar.GetMonthRange(datFrom, datUntil, GMR_DAYSTATE);
auto pDayState = new MONTHDAYSTATE[iMonthCount];
if (pDayState != nullptr)
{
InitDayStateArray(iMonthCount, pDayState, datFrom);
VERIFY(rCalendar.SetDayState(iMonthCount, pDayState));
delete[] pDayState;
}
}
Method 2
void CMeetingScheduleAssistantDlg::OnGetDayStateEnd(NMHDR* pNMHDR, LRESULT* pResult)
{
NMDAYSTATE* pDayState = reinterpret_cast<NMDAYSTATE*>(pNMHDR);
MONTHDAYSTATE mdState[3]{}; // 1 = prev 2 = curr 3 = next
const COleDateTime datStart(pDayState->stStart);
if (pDayState != nullptr)
{
InitDayStateArray(pDayState->cDayState, &mdState[0], datStart);
pDayState->prgDayState = &mdState[0];
}
if (pResult != nullptr)
*pResult = 0;
}
Perhaps if the container for the LPMONTHDAYSTATE information is tweaked somehow it would contribute to resolve this span issue?
Sample code provided by Microsoft used to be published as code that compiles both with a C and C++ compiler. That limits availability of language features, frequently producing code that particularly C++ clients shouldn't be using verbatim.
The case here being the BOLDDAY function-like macro, that's working around not having reference types in C. C++, on the other hand, does, and the macro can be replaced with a function instead:
void bold_day(DWORD& day_state, int const day) noexcept {
if (day > 0 && day < 32) {
day_state |= (0x00000001 << (day - 1));
}
}
Using this function in place of the BOLDDAY macro silences the C26481 diagnostic.
While that works, I'm at a complete loss to understand where the compiler is seeing pointer arithmetic in the macro version. Regardless, replacing a function-like macro with an actual function (or function template) where possible is always desirable.
Update
Things are starting to make sense now. While replacing the function-like macro with a function, as suggested above, is desirable, it will not resolve the issue. My test happened to have used pDayState[0] which still raises C26481 for the macro, but not for the function. Using pDayState[1] instead, the diagnostic is raised in either case.
Let's put the pieces of the puzzle together: Recall that the array subscript expression p[N] is exactly identical to the expression *(p + N) when p is a pointer type and N an integral type. That explains why the compiler is complaining about "pointer arithmetic" when it sees pDayState[iMonth].
Solving that is fairly straight forward. As suggested by the diagnostic, use a std::span (requires C++20). The following changes to InitDayStateArray() make the C26481 diagnostic go away:
void CMeetingScheduleAssistantDlg::InitDayStateArray(int iMonthCount,
LPMONTHDAYSTATE pDayState,
COleDateTime datStart)
{
std::span const day_month_state(pDayState, iMonthCount);
// ...
// memset(pDayState, 0, sizeof(MONTHDAYSTATE)*iMonthCount);
std::fill(begin(day_month_state), end(day_month_state), 0);
// ...
do
{
// ...
{
bold_day(day_month_state[iMonth], datDay.GetDay());
}
}
if (m_Reminders.HasReminder(datDay))
{
bold_day(day_month_state[iMonth], datDay.GetDay());
}
// ...
} while (iMonth < day_month_state.size());
}
A std::span "describes an object that can refer to a contiguous sequence of objects". It takes the decomposed pointer and size arguments that describe an array and reunites them into a single object, recovering the full fidelity of the array.
That sounds great. But remember, this is C++, and there's a caveat: Just like its evil C++17 ancestor std::string_view, a std::span is an unhesitating factory for dangling pointers. You can freely pass them around, and hang on to them far beyond the referenced data being alive. And this is guaranteed for every specialization, starting with C++23.
The other issue is, that addressing this one diagnostic now has several others pop out of nowhere, suggesting that std::span isn't good enough, and gsl::span should be used instead. Addressing those would probably warrant another Q&A altogether.
I am fairly new to C++. I was practicing some ds,algo.This code looks fine to me, but I am getting some error about function not taking 2 arguments. Though I get some error asked in stackoverflow none of the cases match my problem.
#include <iostream>
#include <algorithm>
int ropecutting(int n, int *cuts){
if (n == 0)
return 0;
if (n < 0)
return -1;
int res = std::max(ropecutting(n-cuts[0], cuts), ropecutting(n-cuts[1], cuts), ropecutting(n-cuts[2], cuts));
if(res == -1) return -1;
return res+1;
}
int main(){
int n, cuts[3];
std::cin >> n;
for(int i = 0; i < 3; i ++)
std::cin >> cuts[i];
std::cout << ropecutting(n, cuts);
}
The error I get is,
main.cpp
G:\software_installation\Visual Studio Community 2017\VC\Tools\MSVC\14.16.27023\include\xlocale(319): warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc
G:\software_installation\Visual Studio Community 2017\VC\Tools\MSVC\14.16.27023\include\algorithm(5368): error C2064: term does not evaluate to a function taking 2 arguments
G:\software_installation\Visual Studio Community 2017\VC\Tools\MSVC\14.16.27023\include\algorithm(5367): note: see reference to function template instantiation 'const _Ty &std::max<int,int>(const _Ty &,const _Ty &,_Pr) noexcept(<expr>)' being compiled
with
[
_Ty=int,
_Pr=int
]
G:\software_installation\Visual Studio Community 2017\VC\Tools\MSVC\14.16.27023\include\algorithm(5368): error C2056: illegal expression
Wishing someone would point me out in the right direction. Thank you.
Of the overloads of std::max, the only one which can be called with three arguments is
template < class T, class Compare >
constexpr const T& max( const T& a, const T& b, Compare comp );
So since it receives three int values, that function is attempting to use the third value as a functor to compare the other two, which of course doesn't work.
Probably the simplest way to get the maximum of three numbers is using the overload taking a std::initializer_list<T>. And a std::initializer_list can be automatically created from a braced list:
int res = std::max({ropecutting(n-cuts[0], cuts),
ropecutting(n-cuts[1], cuts),
ropecutting(n-cuts[2], cuts)});
Following code in MSVC generates warning about assignment in conditional expression.
https://godbolt.org/z/i_rwY9
int main()
{
int a;
if ((a = 5)) {
return 1;
}
return a;
}
Note that I tried to use the double () around if since that makes the warning go away with g++, but I do not know how to make it go away in msvc without extracting the assignment from condition.
Is there a way to nudge msvc to figure out that this assignment is intentional?
I know I can use pragmas to disable this warning, but pattern is very common so I would like to get a solution without pragmas if one exists.
The MSVC compiler will give this warning unless you can convince it that you really do know what you're doing. Adding at least one 'real' logical test will achieve this:
int main()
{
int a;
if ((a = 5) != 0) {
return 1;
}
return a;
}
Note that the constant 5 can readily be replaced with any variable or valid expression: adding the explicit != 0 test does nothing to actually change the outcome of the code (and it is unlikely to change the generated assembly).
We have a heap-allocated array of custom structures that is pointed to by a local pointer. The pointer to the array is checked for nullptr. However, during my loop, VC++ complains that the first attempt to use an indexed entry in the array is "Dereferencing NULL pointer 'ppi'".
I'm having a dumb moment here I think, but there doesn't seem to be any way to satisfy the 6011 warning... how do I correct this scenario?
I have included some snippets of code to briefly illustrate the code in question.
// Previously, SystemInfoObject.PeripheralPortInfo is heap-alloc'd to contain
// multiple PeripheralInfo structures, and
// SystemInfoObject.PeripheralPortInfoCount is adjusted to the number
// of elements.
PeripheralInfo *ppi = nullptr;
ppi = SystemInfoObject.PeripheralPortInfo; // Set our local pointer
if (ppi != nullptr)
{
for (int i = 0; i < SystemInfoObject.PeripheralPortInfoCount; i++)
{
if (_tcsncmp(ppi[i].PortName, _T("\\\\"), 2) == 0) // C6011
{
// Some code
}
}
}
Visual Studio strikes again, I didn't see the loop condition that required certain code later on to change the pointer ppi and the null condition was never re-checked on subsequent loop iterations.
Wish I could delete my question! All set!
I'm creating my first program on Winform with C++. I have a function and a string input. However, when I run the program, I get the following error with text.size(): "Error C2228 left of '.size' must have class/struct/union"
Relevant code:
private: System::Void bntGet_Click(System::Object^ sender, System::EventArgs^ e) {
in_itext = txtText->Text;
itext = Convert::ToString(in_itext);
for (Int32 index = 1; index <= itext.size(); index++)
{
if (itext[index] == '#')
{
while (itext[index - 1] != ' ')
{
index--;
}
while (itext[index] != ' ')
{
next_email += itext[index];
index++;
if (itext[index] == '\0')
break;
}
break;
}
}
txtEmail->Text = next_email;
}
Any suggestions? Thanks everyone!
Standard warning: While it's certainly possible to write the main body of your application in C++/CLI, or even write the GUI in C++/CLI using WinForms, it is not recommended. C++/CLI is intended for interop scenarios: where C# or other .Net code needs to interface with unmanaged C++, C++/CLI can provide the translation between the two. For primary development, it is recommended to use C# with either WinForms or WPF if you want managed code, or C++ with MFC if you want unmanaged.
That said:
for (Int32 index = 1; index <= itext.size(); index++)
and
"Error C2039 'length': is not a member of 'System::String'"
Size is not how you get the length of a System::String in .Net. For that, you want the Length property. You were close on your second attempt, but you need a capital "L". (size() is how std::string does it, but std::string is a completely different beast from System::String.)
Other issues:
in_itext = txtText->Text;
itext = Convert::ToString(in_itext);
It's already a string, you don't need to convert it.
while (itext[index - 1] != ' ')
{
index--;
}
You can easily run off the beginning of the string if you do this. (You'll get an exception when index is equal to zero.) Add a check against zero.
while (itext[index] != ' ')
{
next_email += itext[index];
index++;
if (itext[index] == '\0')
break;
}
Strings in .Net are not null-terminated, you need to check against the Length.
If we take a step back, what problem are you actually trying to solve here? My best guess is that you've got some text with an email address somewhere in the middle, and you just want to extract the email address. If that's the case, then I'd probably try using a regular expression to extract the email address. You've got the full power of the .Net Library available to you, use it! See Using a regular expression to validate an email address for the regex to use, and read up on regular expressions with the introduction page and class reference.