Now getting this error when compiling this macro:
Undefined symbols for architecture x86_64:
"_main", referenced from:
implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
code:
Code:Code:#include <stdio.h> #define swap(t,x,y) \ ( t type = x; x = y; y = type; ) int main() { int x, y; x = 2, y = 10; swap(int, x, y); printf("%d %d\n", x, y); return 0; }
If you have a function-style macro spanning multiple lines like this, enclose it within a do while(0) loop, e.g.,
I have taken the liberty of um, swapping t and type.Code:#define swap(type, x, y) do {\ type t = x;\ x = y;\ y = t;\ } while (0)
You really need to indent your code properly.
Look up a C++ Reference and learn How To Ask Questions The Smart WayOriginally Posted by Bjarne Stroustrup (2000-10-14)
I think that's matter of style. Also, I would prefer variables begin with underscore so that they won't clash with function or variable definitions in header files.If you have a function-style macro spanning multiple lines like this, enclose it within a do while(0) loop
Code:#include <stdio.h> #define SWAP(t,x,y) \ { \ t_type = __x; __x = _y; _y = _type; \ } int main() { int x, y; x = 2, y = 10; SWAP(int, x, y); printf("%d %d\n", x, y); return 0; }
1. The do...while(0) macro trick is not a matter of style, it's to allow the macro to be used in places where a statement normally would be.
2. The underscore trick is only needed for variables you create inside your function-like macro:
Code:#include <stdio.h> #define swap(type, x, y) do {\ type _t = x; /* Naming this t will cause problems */\ /* in the below code. */\ x = y;\ y = _t;\ } while(0) int main(void) { int x = 100; int t = 200; int y = 300; printf("Swap x/t or t/y? [1/2]: "); char resp = getchar(); if (resp == '1') swap(int,x,t); /* This will fail unless swap is wrapped with do {...} while(0) */ else swap(int,t,y); printf("%d %d %d\n", x, t, y); return 0; }
