On 02/03/2018 15:38, Jonathan Wakely wrote:
> On 2 March 2018 at 14:27, Mason wrote:
>
>> I am confused by both of these warnings.
>> I am aware that adding two 60-char strings might overflow an 80-char buffer,
>> which is why I'm using snprintf.
>
> In which case the output would be truncated instead of overflowing,
> and that's what the warning says.
>
>> I'm not sure these warnings are very helpful. What am I missing?
>> (I may have oversimplified the testcase.)
>
> I think the point is that although you avoid undefined behaviour, you
> might still not get the output you expected.
To provide some context, I am using the following struct:
struct expr
{
int val;
char txt[60];
};
to store symbolic arithmetic expressions.
I start with simple symbolic constants "a", "b", "c", etc
and build up more complex expressions, such as "(a + b)" and "((a + b) * c)"
Actual code, for example,
struct expr bak = tab[i];
snprintf(tab[i].txt, 60, "(%s + %s)", bak.txt, tab[j].txt);
Is there a different way to write this code to avoid the warning(s) or should
I just disable Wformat-truncation?
(I hate disabling warnings, but this one looks irrelevant, in my situation.)
Regards.
