# V124. Function 'Foo' writes/reads 'N' bytes. The alignment rules and type sizes have been changed. Consider reviewing this value.

The analyzer detected a potential error: the size of data being written or read is defined by a constant.

When the code is compiled in the 64-bit mode, the sizes of some data and their alignment boundaries will change. The sizes of base types and their alignment boundaries are shown in the picture:

The analyzer examines code fragments where the size of data being written or read is defined explicitly. The programmer must review these fragments. Here is a code sample:

    size_t n = fread(buf, 1, 40, f_in);

Constant 40 may be an incorrect value from the viewpoint of the 64-bit system. Perhaps you should write it so:

    size_t n = fread(buf, 1, 10 * sizeof(size_t), f_in);