In the final binary, it would not be stored at all. The idea is that if you have can use the location as a template parameter, you can generate an unique symbol

In the final binary, it would not be stored at all. The idea is that if you have can use the location as a template parameter, you can generate an unique symbol for it (say, a function) and log that address instead, stripping the actual function name from the binary. When reading the log you can map the function address to the function name and recover the source_location from that (but I'm not familiar with the actual process). The key is that the mapping need not be stored in the binary. As shown else thread, you can easily compute the size of std::source_location::current().file_name() at compile time. The only limitation is that neither source_location nor the std::source_location::current().file_name() pointer themselves can be used directly as non-type template parameters. But there are ways around that. And yes, you can do the same with __FILE__ and __LINE__, but you need to wrap them in a macro for usability. The question is whether there is a solution that doesn't use macros at all (I posted one elsethread).