macOS Warning :suggest parentheses around assignment used as truth value

[roublesaha]

Hi
I am using this snippet of code

void * handle_;

if (handle_ =dlopen("/System/Library/Frameworks/DiskArbitration.Framework/Versions/A/DiskArbitration",RTLD_NOW))
{
printf("............");

}
else if (handle_ =dlopen("/System/Library/PrivateFrameworks/DiskArbitration.Framework/Versions/A/DiskArbitration",RTLD_NOW))
{
printf(".................");
}

But i am getting the warning :
"suggest parentheses around assignment used as truth value" for the first line i,e the for the "for" loop....can somebody help me to get rid of this warning..

 

[kpua]

First off, it's generally bad form to have side-effects in if() statements.

However, sometimes it's the simplest way to code what you mean (though I don't think it is in your example necessarily). When you do have an assignment in an if statement, GCC generally expects something like this:

if ( (foo = bar()) != NULL )

Notice the extra parentheses around the assignment. GCC suggests you use the parentheses to avoid the following error:

if ( foo = bar() != NULL )

which wouldn't check for the value assigned to foo being equal to NULL, but rather assign the boolean (bar() != NULL) to foo.

It's also customary and generally more clear to have the explicit boolean check in there, so that's why GCC expects this.

 

[Sander]

It is also because the statement

if (a = b) {...}

is correct C (assign b to a and check for non-zero), but most often people really meant

if (a == b) {...}

Since assignment inside the if() is the exception, GCC issues a warning about it. Also for future readers of your code, the extra parentheses indicate "yes, I really mean assignment here".