MISRA-C：强制转换文字数字

Question

I read a source code, there is a statement like: uint32 XYZ; ... XYZ = (uint32)0x0000000U.

I wonder if the cast is necessary, is XYZ = 0U OK?

Thanks

Answer 1

The integer constant 0U can in theory be an unsigned int of 64 bits. If so, the cast is necessary since MISRA-C (2012 10.3) does not allow implicit conversion to a narrower type. However, the cast isn't necessary on 32 bit CPUs and smaller.

An alternative is to write uint32_t XYZ = UINT32_C(0); in which case the compiler picks the appropriate type for the integer constant automatically.