clang does catch this: clang -Weverything uninit.c uninit.c:3:6: warning: no previous prototype for function 'foo' [-Wmissing-prototypes] void foo(int b

clang does catch this: clang -Weverything uninit.c uninit.c:3:6: warning: no previous prototype for function 'foo' [-Wmissing-prototypes] void foo(int bar) { ^ uninit.c:10:6: warning: variable 'lol' may be uninitialized when used here [-Wconditional-uninitialized] if (lol == 7) { ^~~ uninit.c:4:9: note: initialize the variable 'lol' to silence this warning int lol; ^ = 0 uninit.c:37:3: warning: no newline at end of file [-pedantic,-Wnewline-eof] */ ^ 3 warnings generated.