# V122. Memsize type is used in the struct/class.

Sometimes you might need to find all the fields in the structures that have a memsize-type. You can find such fields using the V122 diagnostic rule.

The necessity to view all the memsize-fields might appear when you port a program that has structure serialization, for example, into a file. Consider an example:

    struct Header
    {
      unsigned m_version;
      size_t m_bodyLen;
    };
    ...
    size_t size = fwrite(&header, 1, sizeof(header), file);
    ...

This code writes a different number of bytes into the file depending on the mode it is compiled in - either Win32 or Win64. This might violate compatibility of files' formats or cause other errors.

The task of automating the detection of such errors is almost impossible to solve. However, if there are some reasons to suppose that the code might contain such errors, developers can once check all the structures that participate in serialization. It is for this purpose that you may need a check with the V122 rule. By default it is disabled since it generates false warnings in more than 99% of cases.

In the example above, the V122 message will be produced on the line "size_t m_bodyLen;". To correct this code, you may use types of fixed size:

    struct Header
    {
      My_UInt32 m_version;
      My_UInt32 m_bodyLen;
    };
    ...
    size_t size = fwrite(&header, 1, sizeof(header), file);
    ...

Let's consider other examples where the V122 message will be generated:

    class X
    {
      int i;
      DWORD_PTR a; //V122
      DWORD_PTR b[3]; //V122
      float c[3][4];
      float *ptr; //V122
    };

V117 is a related diagnostic message.

Note. If you are sure that structures containing pointers will never serialize, you may use this comment:

    //-V122_NOPTR

It will suppress all warnings related to pointers.

This comment should be added into the header file included into all the other files. For example, such is the "stdafx.h" file. If you add this comment into a "*.cpp" file, it will affect only this particular file.