# The warnings C4311 and C4312 generated by the compiler when using the /Wp64 switch

C4311 and C4312 are ones of the most frequent warnings generated by the compiler for 32\-bit code not adapted for migration to 64\-bit platforms\. They are generated only when you use the /Wp64 key \(detecting 64\-bit portability issues\) intended to prepare migration of applications to 64\-bit systems\.

Note that the /Wp64 parameter is announced deprecated beginning with Visual C\+\+ 9\.0 since the time "to prepare for 64\-bit code" [has passed](https://pvs-studio.com/en/blog/posts/cpp/a0021/)\.

The C4311 and C4312 warnings tell you about an attempt to put a pointer into a 32\-bit variable or vice versa\. In a 64\-bit system, these conversions are incorrect\. If the code is compiled on the 64\-bit platform, the pointer's value \(64 bits\) will be truncated if it is assigned to a variable of the int type \(32 bits\)\. This is an example of code that causes the C4311 and C4312 warnings:

```cpp
   int *p;
   int a = (int)p; //C4311
   p = (int *)a; //C4312
```

To correct the code you should use [memsize\-types](https://pvs-studio.com/en/blog/terms/0030/) that can store a pointer, for instance size\_t, ptrdiff\_t, intptr\_t, LONG\_PTR, etc\. This is an example of correct code:

```cpp
   int *p;
   INT_PTR b = (INT_PTR)p; //OK
```

See the "[Development of 64\-bit C/C\+\+ applications](https://pvs-studio.com/en/blog/lessons/)" course for detailed recommendations on creating safe 64\-bit code\.

If a program being developed has a short life\-cycle and you do not plan to port it to the 64\-bit platform, you may eliminate these warnings by disabling the /Wp64 option in the compiler settings\. 

Note that the /Wp64 switch carries out a rather superficial analysis and detects only crudest errors\. To perform a complete analysis of your code, we recommend you to use the specialized static code analyzer Viva64 included into the [PVS\-Studio](https://pvs-studio.com/en/pvs-studio/) package\. See the article "[Comparing capabilities of PVS\-Studio and Visual Studio 2010 in detecting defects in 64\-bit programs](https://pvs-studio.com/en/blog/posts/a0066/)" for comparison of diagnostic abilities of Visual C\+\+ and Viva64\.

## References

1. Andrey Karpov\. [64 bits, Wp64, Visual Studio 2008, Viva64 and all the rest\.\.\.](https://pvs-studio.com/en/blog/posts/cpp/a0021/)
1. MSDN Library\. [Compiler Warning \(level 1\) C4311](https://msdn.microsoft.com/en-us/library/4t91x2k5(VS.90).aspx)
1. MSDN Library\. [Compiler Warning \(level 1\) C4312](https://www.microsoft.com/en-us/download/details.aspx?id=55984)