Avoiding Field Alignment Problems in C/C++ Structures

All fields defined in ILE C/C++ structures are aligned on their natural boundaries. For example, int fields are four bytes long and are stored on four-byte boundaries. If you create a file that is externally described, the system does not enforce boundary alignment of the externally described data. The structure may need to be packed because packed structures match the alignment of the externally described data.

If the fields defined in the DDS are aligned (for example, all are character fields), you can use the type definition that is generated without packing the structure.

To avoid an alignment problem, specify the _P option to generate a packed structure. For example, to include a packed type definition structure of input and key fields for the record format custrec from the file EXAMPLE/CUSTMSTL, the following statements must appear in your program in the order shown below:

   #pragma mapinc("custmf","EXAMPLE/CUSTMSTL(custrec)","input key","_P")
   ...
   #include "custmf"