Difference between macros with and without using do ... while

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?

Note: `FREE1` contains a terminating semicolon that it shouldn't. — Daniel Fischer, Dec 21 '12 at 15:44

score 4 · Answer 1 · answered Dec 21 '12 at 15:43

4

It might be more satisfying to figure this one out yourself.

Hint:

if(y) FREE2(x);

answered Dec 21 '12 at 15:43

geocar

score 4 · Accepted Answer · answered Dec 21 '12 at 15:44

4

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

answered Dec 21 '12 at 15:44

simonc

2 Answers2