1998 vintage C code now fails to compile under gcc

Question

I have ~16k lines of 1998 vintage C code (~50 main progs) which built flawlessly under gcc at that time but now fails with many \"lvalue required as left operand of assignme

Answer 1

In addition to changing the code to take an address, cast the pointer, and dereference, it will likely also be necessary to employ the "no_strict_aliasing" option. C99 added some rules, with the intention of facilitating optimization, which negate C's model of the system state as being a bunch of unsigned char[]. The most infamous of these is the Strict Aliasing Rule. While code which casts pointers as a means of saying "interpret the thing pointed to by this pointer as a X" may compile, writing to a pointer using one type and reading using another will generally yield Undefined Behavior, and some compilers will interpret that as license to behave in rather strange and bizarre ways unconstrained by laws of time and causality.