April 17, 2018
I’ve built a fun little tool to help understand the way a C or C++ compiler will
layout members in a struct or class. Behold, Struct
Layout. This tool uses the
Layout utility behind the scenes. Layout
parses C and C++ code using libclang. It generates C code with proper
offsetof operators to output a table including the size of each type, the size,
offset, and padding for each field.
This information can be useful, as it may be surprising how a compiler lays out a given type in memory. The compiler may need to deal with platform-specific alignment requirements for certain types. If you are writing cross-platform code, it can be useful to understand how compilers behave on all of your target platforms.
If you are thinking about data-oriented design, data layout can be rather important. Knowing the number of object which fit into a cache line can inform your decisions about how algorithms can best make use of processor and memory resources.
I’ve already found this tool useful for day-to-day work, I hope that you do as well!