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c++visual-studioc++11c++-cliwarnings

Getting Warning C6385 if try to use function

I get this warning if I try to use function geti() in the following code. 

Warning C6385   Reading invalid data from 'snapPts':  the readable size is '((geti()+1))*sizeof(DPoint3d)' bytes, but '48' bytes may be read.

But If I use integer like

int i

directly then I am not able to get the warning. I am unable to understand the scenario that what’s happening there, I googled it much but couldn’t find the solution. I am new to c++, please pardon me for spell mistake and please help me to understand this.

Note: I am building the code with "Microsoft Mixed(C++/CLR) Recommended Rules.

I am using the following code

#include <windows.h>  
#include <stdio.h>  
#include <malloc.h>
#include <corecrt_wstring.h>

int geti() {
return 2;
}
struct  DPoint3d
{
//! x coordinate
double x;
//! y coordinate
double y;
//! z coordinate
double z;
};

int main(array<System::String ^> ^args)
{

int i = 2;


if (i > 1) {

    DPoint3d*   snapPts = (DPoint3d *)_alloca((geti() + 1) * sizeof(DPoint3d));

    DPoint3d* snapPts2 = new DPoint3d();

    *snapPts2 = snapPts[1];


}

return 0;
}

A great answer is really appreciated.

Thanks

Solution

  • The message comes out of Visual Studio's static code analyzer, not the compiler. The analyzer is relatively new and does not work very well - it shows a lot of false positives. In your case, it simply did not notice that geti() always returns 2.

    The real problem in your code is that *snapPts2 = snapPts[1]; uses uninitialized memory. This is because _alloca allocates memory from the stack, but does not initialize it.