Question

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Do-While and if-else statements in C/C++ macros

I have the following macros :

#define FREE1(x) do { free(x); x = NULL; } while (0)
#define FREE2(x) free(x); x = NULL

What is the difference between these macros?

Answer 1

Consider the following example

if (some_test) FREE2(x);

expands to

if (some_test)
    free(x);
x = NULL; // happens regardless of value of some_test