When I try to compile the piece of code below, I get this warning:
warning: suggest parentheses around assignment used as truth value
Why does this happen? This is a rather common idiom, I believe. I even use something like it earlier on my code.
struct PIDList* getRecordForPID(struct PIDList* list, pid_t pid) { while(list = list->next) if (list->pid == pid) return list; return NULL; } Be explicit - then the compiler won't warn that you perhaps made a mistake.
while ( (list = list->next) != NULL ) or
while ( (list = list->next) ) Some day you'll be glad the compiler told you, people do make that mistake ;)
if (0 == varName) in C, so that I could get an error message if I mistyped it.
While that particular idiom is common, even more common is for people to use = when they mean ==. The convention when you really mean the = is to use an extra layer of parentheses:
while ((list = list->next)) { // yes, it's an assignment It's just a 'safety' warning. It is a relatively common idiom, but also a relatively common error when you meant to have == in there. You can make the warning go away by adding another set of parentheses:
while ((list = list->next)) This error may also occur when
if(x = 10) // this is incorrect if(x == 10) // this is correct 
-Wno-parentheses(I believe that's the right one) to disable this specific warning. However, if you're that absent-minded, be careful not to write=instead of==...