When implementing an infinite loop, is there a difference in using while(1) vs for(;;) vs goto (in C)?

Question

When implementing an infinite loop, is there a difference in using while(1) vs for(;;) vs goto?

Thanks, Chenz

Answer 1

while(1) and for(;;) are exactly equivalent and both are well-understood idioms to code infinite loops.

I would avoid the use of goto: to break from an infinite loop or to proceed to the next iteration, use break and continue.

Answer 2

From what I recall of my "disassembling years", it won't make much a difference (compilers are smart enough). It is more about aesthetics IMO.

Answer 3

In C, true is implemented as follows (depending on compiler)

#define TRUE 1

or

#define TRUE (-1)

AND false is implemented as

#define FALSE 0

so while (1) is equivalent to while (true) since 0 is considered false.

the while (1) == for (; ;) as there are no stopping condition.

which is translated to assembler as

:loop
  ...
  ...
  ...
  goto loop

so if the assembler code doesn't have a ret or exit instruction, it's considered a infinite loop.

Answer 4

None. Use what is the most readable to you

Answer 5

I just compared the unoptimized assembler output of gcc:

# cat while.c 
int main() {
    while(1) {};
    return 0;
}

# cat forloop.c 
int main() {
    for (;;) { };
    return 0;
}

Make assembler output:

# gcc -S while.c 
# gcc -S forloop.c 

Compare assembler files:

# diff forloop.s while.s
1c1
<   .file   "forloop.c"
---
>   .file   "while.c"

As you can see there are no significant differences. Here is the output

# cat while.s 
    .file   "while.c"
    .text
.globl main
    .type   main, @function
main:
    pushl   %ebp
    movl    %esp, %ebp
.L2:
    jmp .L2                    # this is the loop in both cases
    .size   main, .-main
    .ident  "GCC: (GNU) 4.4.3"
    .section    .note.GNU-stack,"",@progbits

While this is not a technical proof that they are the same, I'd say it is in 99.9% of the cases.

Answer 6

There is hardly any difference in generated assembly. It's more of an stylistic issue:

Goto - just ooogly: jumps backward, no explicit infinite block

while(1) - better, requires "dummy" condition though and you'll be often warned by compiler(warning level 4) or static analysis tool

for(;;) might not be the prettiest, but imho fits best because this construct cannot have any other meaning (compared to while). But some other people prefer while(1) for the "same" reason...