Global variables, re-entry code, and thread safety

Question

I am trying to decide whether to perform certain operations as macros or as functions.

Let's say, as an example, I have the following code in the header file:

extern int x_GLOB;
extern int y_GLOB;

#define min(x,y) ((x_GLOB = (x)) < (y_GLOB = (y))? x_GLOB : y_GLOB)

the goal is for each single argument to be evaluated only once ( min(x++,y++)it will not cause any problems here).

The question is: do two global variables have any problems in terms of re-entering code or thread safety?

I would say no, but I'm not sure.

What about:

#define min(x,y) ((x_GLOB = (x)), \
                  (y_GLOB = (y)), \
                  ((x_GLOB < y_GLOB) ? x_GLOB : y_GLOB)

will it be another case?

Please note that the question is not "generally", but because these global variables are used only inside this macro and to evaluate a single expression.

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Answer 1

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int a = min(min(1, 2), min(3, 4));

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• min (1, 2) x_GLOB ( ):
  • x_GLOB = 1
  • y_GLOB = 2
  • min, 1, x_GLOB ( )
• min (3, 4) y_GLOB ( ):
  • x_GLOB = 3 (uh-oh, 1 )
  • y_GLOB = 4
  • min, 3, y_GLOB ( )
• min (a, b), a - min (1, 2) b - min (3, 4)
  • min x_GLOB ( 3) y_GLOB ( 3)
  • 3

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Answer 2

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1:

#define MIN(x, y) ((x) < (y) ? (x) : (y))

2:

int min(int x, int y) { return x < y ? x : y; }

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3:

#define min(x, y) ({ \
    typeof(x) x__ = (x); \
    typeof(y) y__ = (y); \
    x__ < y__ ? x__ : y__; \
})

Answer 3

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Answer 4

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Answer 5

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x_GLOB 3, y_GLOB - 4.

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#define STATIC_INLINE static

STATIC_INLINE int min_func(int x, int y) { return x < y ? x : y; }

#define min(a,b) min_func((a),(b))

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Answer 6

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