Good C-coding style for multiple lines if conditions

Question

I am programming a project in C and have a problem: I've got a lot of if conditions and it might get really hard for other people to read. I haven't yet found a similar question on the internet.

Do you have an idea or example how to make my code more readable?

Here is the C Code:

if( ((g_cycle_cnt == uartTxSecondaryMsg[3][msgPos[3]].sliceNo) ||   //correct slicenumber...
    (uartTxSecondaryMsg[3][msgPos[3]].sliceNo == -1) ||             // or as fast as possible...                                            

  ( (uartTxSecondaryMsg[3][msgPos[3]].sliceNo == -2) &&
   ((uartTxSecondaryMsg[3][msgPos[3]].timeFrameBegin>=g_uptime_cnt) && 
    (uartTxSecondaryMsg[3][msgPos[3]].timeFrameEnd<=g_uptime_cnt)))) &&

   ((dataProcessingFlag & SECONDARY_MSG_ANNOUNCED_CH4) == SECONDARY_MSG_ANNOUNCED_CH4) )

Answer 1

Create functions that have indicative names that check the requirements and represent their meaning e.g:

if( is_correct_slice_number(/*... params here ... */) || 
    is_asap(/*... params here ... */)  || 
    is_other_condition(/*... params here ... */))

Or as suggested macros that follow the same logic e.g:

if( IS_CORRECT_SLICE_NUMBER(/*... params here ... */) || 
    IS_ASAP(/*... params here ... */)  || 
    IS_OTHER_CONDITION(/*... params here ... */))

I think that this might make your intentions clearer.

Answer 2

If you want to stick with your existing code (as opposed to factor things out into inline functions), and just modify the indentation, I'm a big fan of using indent consistently. This means you can fix any source file.

With its default options it gives you GNU indentation, i.e.:

if (((g_cycle_cnt == uartTxSecondaryMsg[3][msgPos[3]].sliceNo) ||       //correct slicenumber...
     (uartTxSecondaryMsg[3][msgPos[3]].sliceNo == -1) ||        // or as fast as possible...
     ((uartTxSecondaryMsg[3][msgPos[3]].sliceNo == -2) &&
      ((uartTxSecondaryMsg[3][msgPos[3]].timeFrameBegin >= g_uptime_cnt) &&
       (uartTxSecondaryMsg[3][msgPos[3]].timeFrameEnd <= g_uptime_cnt)))) &&
    ((dataProcessingFlag & SECONDARY_MSG_ANNOUNCED_CH4) ==
     SECONDARY_MSG_ANNOUNCED_CH4))
  {
    /* do something */
  }

I'd say that the problem here is in fact that you are poking about illegibly in arrays. At the very least, factor out:

uartTxSecondaryMsg[3][msgPos[3]]

into a separate variable, e.g.:

whatever *foo = &uartTxSecondaryMsg[3][msgPos[3]];
if (((g_cycle_cnt == foo->sliceNo) ||   //correct slicenumber...
     (foo->sliceNo == -1) ||    // or as fast as possible...
     ((foo->sliceNo == -2) &&
      ((foo->timeFrameBegin >= g_uptime_cnt) &&
       (foo->timeFrameEnd <= g_uptime_cnt)))) &&
    ((dataProcessingFlag & SECONDARY_MSG_ANNOUNCED_CH4) ==
     SECONDARY_MSG_ANNOUNCED_CH4))
  {
    /* do something */
  }

Obviously choose an appropriate type and variable name for foo.

You could then separate out the limbs of the if statement into separate functions each taking foo as a parameter.

Answer 3

[this is very subjective]

• remove excessive parentheses; they are defensive and obscure the meaning
• properly align and order the conditions (possibly ignoring indentation rules)
• (maybe) rewrite into another construct, such as a switch, or using early returns, or even goto

---

First step (cleanup and alignment):

if (    (  uartTxSecondaryMsg[3][msgPos[3]].sliceNo == g_cycle_cnt //correct slicenumber...
        || uartTxSecondaryMsg[3][msgPos[3]].sliceNo == -1          // or as fast as possible...                                
        ||(uartTxSecondaryMsg[3][msgPos[3]].sliceNo == -2
             && uartTxSecondaryMsg[3][msgPos[3]].timeFrameBegin >= g_uptime_cnt
             && uartTxSecondaryMsg[3][msgPos[3]].timeFrameEnd <= g_uptime_cnt
             && (dataProcessingFlag & SECONDARY_MSG_ANNOUNCED_CH4) == SECONDARY_MSG_ANNOUNCED_CH4 ) ) 
                {
                // do something useful here
                }

---

Second step, using switch (and goto !) [this could be a bit too much for some readers ...]

switch (uartTxSecondaryMsg[3][msgPos[3]].sliceNo) {
default:
    if (uartTxSecondaryMsg[3][msgPos[3]].sliceNo == g_cycle_cnt) goto process;
    break;
case -2:
    if (uartTxSecondaryMsg[3][msgPos[3]].timeFrameBegin < g_uptime_cnt) break;
    if (uartTxSecondaryMsg[3][msgPos[3]].timeFrameEnd > g_uptime_cnt) break;
    if ((dataProcessingFlag & SECONDARY_MSG_ANNOUNCED_CH4) != SECONDARY_MSG_ANNOUNCED_CH4) break;
case -1:
process:

          // do something useful here
 }

---

The advantage of the switch() construct is that it immediately clear that uartTxSecondaryMsg[3][msgPos[3]].sliceNo is the master condition. Another advantage is that cases and conditions can be added without having to interfere with the other cases or to struggle with the parentheses.

Now I hope I got the parentheses-removal right...