How to write a "dummy" (do nothing) line in C

Question

Is there a dedicated way to write a dummy line in C? (kind of like pass in Python) If you are wondering why I don't just leave a blank line, I need something that I can attach an Xcode breakpoint to-- if there is nothing there the breakpoint will skip to the next line!! So far I've been using sleep(0) for this purpose. I was wondering if there was a better/more efficient/more official way to accomplish this.

Oh, and I'm using Objective-C, so if there is anything that was added in Obj-C that fits this purpose, feel free to include it.

Why do you need to make an Xcode breakpoint on an empty line, anyway? — Eliza Wilson, Mar 08 '14 at 02:46

Enrico Susatyo · Answer 1 · 2016-04-26T02:13:12.623

25

Put a semi colon. It works in C and Obj-C (and Java, and Swift, and many other languages).

edited Apr 26 '16 at 02:13

answered Mar 08 '14 at 02:43

Enrico Susatyo

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I thought this would work, but putting a breakpoint in this line causes XCode to stop at the next line. – Merlevede Mar 08 '14 at 03:02

score 8 · Answer 2 · answered Mar 08 '14 at 02:45

8

sleep(0) works, so does a null statement (just a semicolon ; on a single line) and the statement i+1;

Compiler optimization will usually result in no machine code being generated for these statements.

answered Mar 08 '14 at 02:45

ElGavilan

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`sleep(0)` requires an #include and that #include is OS-dependent, right? The `;` solution sounds better – WhyWhat Jun 12 '22 at 20:50

score 5 · Accepted Answer · answered Mar 08 '14 at 03:03

5

Add a trivial assignment

var = var;

answered Mar 08 '14 at 03:03

Merlevede

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10

This isn't completely trivial. – nhgrif Mar 11 '14 at 00:18
I am not understanding the keyword `var` in C. – WhyWhat Jun 12 '22 at 20:51
1

@WhyWhat they're just using it as an example, substitute any variable in your program – Patronics Oct 12 '22 at 04:12

score 5 · Answer 4 · edited Mar 19 '21 at 02:42

Most of the answers already posted will do what you want, but if you need a block, try a pair of braces:

{}

And, if you need an actual statement that actually does nothing, and yet will survive compilation, then a little inline assembly can do the trick:

asm("nop");

Technically this isn't portable; but the nop instruction exists in basically any instruction set you care to name. Also guaranteed* not to be compiled out!

score 2 · Answer 5 · answered Mar 08 '14 at 02:47

2

Just put the breakpoint on the first line you don't want executed. The breakpoint stops the execution before the code on that line is executed.

Without creating a "fake" line:

    someMethod();
    // empty line
BREAKPOINT
    someOtherMethod();

With creating a "fake" line:

    someMethod();
BREAKPOINT
    ;
    someOtherMethod();

Both of these result in the exact same result. The breakpoint stops at the same place.

answered Mar 08 '14 at 02:47

nhgrif

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That's the issue- the code sets a variable to a certain type so I can see it in the debugger, but on the next line it falls out of scope- as it should, I only have that in there for debugging. – PopKernel Mar 08 '14 at 02:48
@PopKernel Is that because you did not use braces for your if/loop? You can set the breakpoint on the closing brace. – Enrico Susatyo Mar 08 '14 at 02:49
Then move the breakpoint up a line. If you are stepping through, there will be a line after the variable is set and before it falls out of scope. – nhgrif Mar 08 '14 at 02:50

score 2 · Answer 6 · answered Jul 13 '22 at 18:55

2

The good old (void)0 should do it.

(void)0;

(void) tells the compiler to just ignore the following number 0.

answered Jul 13 '22 at 18:55

Piotr Siupa

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score 1 · Answer 7 · answered Mar 08 '14 at 06:23

1

just place this constant:

0xDEBAF;

answered Mar 08 '14 at 06:23

qulinxao

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Please explain your answer. Now it is not very helpful. – Stefan Apr 30 '21 at 06:53
1

Stefan it just expresion number in hex with view as normal english word like 0xdeadbeef https://en.wikipedia.org/wiki/Hexspeak – qulinxao May 01 '21 at 12:39

score 0 · Answer 8 · answered Mar 31 '23 at 01:08

My compiler optimizes away statements like

(void)0;
;
0xDEBAF;

so it's impossible to put a breakpoint on those statements.

What it doesn't optimize away is statements like:

volatile int g_break;
int myFunction(void) {
  // Break on this line
  (void)g_break;
}

and

int myFunction(void) {
  // Break on this line
  volatile int xyz = 0;
}

where you can put a breakpoint on the line of code inside the function.

score -1 · Answer 9 · answered Oct 16 '17 at 17:47

-1

What about "YES" This is what I use when I wan't to switch off logs

#define Log(s,...) YES

answered Oct 16 '17 at 17:47

Emmanuel Sellier

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How to write a "dummy" (do nothing) line in C

9 Answers9