Whats meaning of this rsAssert macro?

Question

i found this code from here

#if 1
#define rsAssert(v) do {if(!(v)) LOGE("rsAssert failed: %s, in %s at %i", #v, __FILE__, __LINE__);} while(0)
#else
#define rsAssert(v) while(0)
#endif

Question 1:

Here i am not getting why do and while is used here? Is there any special reason for using this?

Question 2:

What is the purpose of doing this all in macro. Why just one dont use assert() ?

i think perhaps there is a valid reason for this..

score 3 · Answer 1 · edited May 23 '17 at 10:34

3

Your first question about why there's a do/while "loop" is covered here: What's the use of do while(0) when we define a macro?

The answer to the second question could be better answered by the code's author, but I guess they wanted to use their own logging system when an assert failed rather than the default one.

edited May 23 '17 at 10:34

Community

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answered Feb 20 '12 at 17:23

John Zwinck

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score 2 · Accepted Answer · answered Feb 20 '12 at 17:26

The do/while is a well-known trick for turning a block of statements into something that syntactically acts like a single statement. It allows use in places like:

if (whatever)
    rsAssert(whatever);
else
    // ...

whereas, most alternatives would produce a syntax error in this case.

As for why using it at all: because it writes output with LOGE instead of printing to stderr, and (unless LOGE does so) this doesn't seem to abort the program like assert will.

score 0 · Answer 3 · answered Feb 20 '12 at 17:25

As asked many times before, the reason a do-while loop is use is for syntactic sugar:

// this line would be valid if a simple if was used:
rsAssert(myAssert)

// with a do-while, however, this is now invalid:
rsAssert(myAssert)

// so, that means you have to add the ';' to make it look like a function call:
rsAssert(myAssert);

Whats meaning of this rsAssert macro?

3 Answers3