Why does the order of a function definition change the output binary?
c
Solution
There is no requirement for the compiler/linker toolchain to produce executables with identical checksums for equivalent programs. In fact, some compilers on certain platforms would produce different executables when the same program is rebuilt twice.
See, for example, exe checksum different after each recompile
You'd have to profile to executable to see if there's any performance difference (in your example, there will almost certainly be none).
Problem
Given these two C programs Function prototype and declaration after.c ``` #include<stdio.h> void hi(); int main(){ hi(); return 0; } void hi(){ puts("hello world"); } ``` Function definition only before.c ``` #include<stdio.h> void hi(){ puts("hello world"); } int main(){ hi(); return 0; } ``` compiled with: cc -oafter after.c cc -obefore before.c md5sum * efac7a08389095a718b7fc9e163719ca after 41e81298acdf96091b4a9326a4557b0c after.c d5b87a14479e764f1c8a8669182773a1 before 924ec57ea6ef7ee306edfd0ec7f5fd54 before.c As you can see, it will produce different binaries. Why is this so? What's so different about before and after? Is there a speed difference?