Detecting semicolon after loop/if brackets

Question

Is there any flag in GCC (like -Wempty-body in clang), that could help me detect semicolons after the braces of while/for loops? Sometimes it is very hard for humans to find these simple mistakes.

int i = 0;
for (i = 0; i < 10; ++i);
{
    cout << i << endl;
}

I use GCC 4.7.3 and clang 3.2-1~exp9ubuntu1.

Edited: I also check if compilers could help me find these mistakes after "if-else statements".

if (i == 0)
{
    cout << i << endl;
}
else;
{
    cout << i << endl;
}

What is interesting gcc is more helpful than clang (with this flags (-Wall -pedantic -Wempty-body) by printing warning:

main.cpp:30:9: warning: suggest braces around empty body in an ‘else’ statement [-Wempty-body]

possible duplicate of [Can gcc accurately catch useless conditionals?](http://stackoverflow.com/questions/851162/can-gcc-accurately-catch-useless-conditionals) — Oliver Charlesworth, Jun 15 '13 at 19:18
On second thoughts, that's not a duplicate, apologies. However, isn't `-Wempty-body` also a GCC flag? — Oliver Charlesworth, Jun 15 '13 at 19:20
This seems to me a very good reason (i.e. other than style) to put starting `{` on the same line as the `if`/`for`/`while` etc. And to have one-liners on the same line as well. — Kninnug, Jun 15 '13 at 19:29
@OliCharlesworth The GCC flag doesn't cover empty for or while loop. From [here](http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html) `Warn if an empty body occurs in an ‘if’, ‘else’ or ‘do while’ statement. This warning is also enabled by -Wextra. ` — FDinoff, Jun 15 '13 at 19:30
I started writing an answer before I'd done full research, but it seems like the statement "like `-Wempty-body` in clang" is a bit misleading. Neither of my versions of g++ (4.6.3) or clang++ (2.9) gives a warning when using `-Wempty-body`. — Mats Petersson, Jun 15 '13 at 22:58
@BenVoigt: "Bastardizing" the for-statement to not have `++i`, but instead doing ` for (i = 0; i++ < 10;);` [yes, I know, it doesn't do the same thing any longer- but this was just to test if it "works"] still doesn't give any warning. — Mats Petersson, Jun 15 '13 at 23:07
Apparently there were too many false positives, and people started arguing how to make presence of a comment or macro (expanding to nothing) inhibit the warning, and at that point the whole idea was just scrapped. http://gcc.gnu.org/ml/gcc-patches/2008-11/msg00361.html — Ben Voigt, Jun 15 '13 at 23:12
@MatsPetersson I'm using `Ubuntu clang version 3.2-1~exp9ubuntu1 (tags/RELEASE_32/final) (based on LLVM 3.2)`. — NiegodziwyBeru, Jun 20 '13 at 19:55
@Kninnug Everything is good until you make simple mistake. There is flag in gcc `-Weffc++` that help you check style guidelines based on Scott Meyers Effective C++. I would be good if compilers similarly could help me with this `;` and suggest to use empty brackets. — NiegodziwyBeru, Jun 20 '13 at 20:26

score 2 · Answer 1 · answered Jun 15 '13 at 19:31

2

try

$gcc -Wempty-body foo.c

or

gcc -Wextra -c foo.c

answered Jun 15 '13 at 19:31

Abhas Tandon

1,859
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3

This doesn't work for gcc/g++ 4.7.2 (or at least on my computer it doesn't) – FDinoff Jun 15 '13 at 19:36

score 1 · Answer 2 · answered Jun 15 '13 at 22:56

The obvious answer here is "compile your code with clang++" (although my 2.9 version for x86-64 doesn't seem to catch this particular problem, just like gcc 4.6.3 doesn't catch it - so I'm not entirely convinced the original premise of the question is valid).

This particular code can avoid this problem by using the form, by giving an error for using i after the for-loop itself:

for(int i = ...)

instead of

int i;
for(i = ...)

Of course, that doesn't work in the case where you want i to have a value after the loop.

[And yes, it's a very annoying error - I've spent several hours staring at the screen to find this sort of bug at times - other times you spot it immediately!]

Detecting semicolon after loop/if brackets

2 Answers2