CCS5.5 Compiler Warning (?!) not a fault : use of "=" where "==" may have been intended

Giorgos Vasilas

In my code i had the following typo fault.

if (xxx=1) {
   ...
}

Instead of having a fault i had a warning !?

Description Resource Path Location Type
#189-D use of "=" where "==" may have been intended main.c /doublesin_creator line 35 C/C++ Problem

The result was that, while i was debugging the code x changed its value to 1 !

A strange compiler beahavior.

Tried it on simpler projects e.g. putting the fault if in main or a function) I had an error as it should...

In my case the faulty if was in function that called a function.

I use CCS 5.5.

over 9 years ago

0 user347219 over 9 years ago

Expert 1240 points

I believe this is correct behavior according to the C language standard(s). I think you will find most compilers work this way.

int func()
{
  return 1;
}

int main()
{
  int x = 0;
  if(x = 1)  // legal: first sets x to 1 and then evaluates the value of x.  Compilers may emit a warning.
  {
  }
  if(func() = 1)  // error: can't assign to the return value of func
  {
  }
  if(x = func())  // legal: calls func, assigns the resulting value to x, and evaluates the value of x
  {
  }
  if(1 = x)  // error: can't assign to constant
  {
  }
  if(1 == x)  // legal: alternative form of if(x == 1) that some people prefer because it catches the case when they accidentally wrote if(1 = x)
  {
  }
  return 0;
}

0 George Mock over 9 years ago

TI__Guru**** 249260 points

Add the build option --display_error_number, and you'll see that the numeric ID for this diagnostic is 189.

$ armcl --display_error_number file.c
"file.c", line 5: warning #189-D: use of "=" where "==" may have been intended

Now that you know the ID, you can use --diag_error to elevate that diagnostic from a warning to an error ...

$ armcl --display_error_number --diag_error=189 file.c
"file.c", line 5: error #189-D: use of "=" where "==" may have been intended
1 error detected in the compilation of "file.c".

>> Compilation failure

More on this topic can be learned by watching the video below.

Thanks and regards,

-George

Code Composer Studio™︎

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CCS5.5 Compiler Warning (?!) not a fault : use of "=" where "==" may have been intended