Unexpected C string definition behaviour

Question

As far as I know the below code should not work. Yet, somehow this is OK on my compiler. Please could someone explain.

int main()
{
    char *string;
    string = "Goo";
}

**Why** did you expect it not to "work"??? This is the most important part of the question that you somehow omitted. — AnT stands with Russia, Jun 22 '15 at 19:25
Code should be `const char *string;`. When `const` was introduced, that "should be" was not specified as it was expected to break too much prior code. — chux - Reinstate Monica, Jun 22 '15 at 19:48

Sourav Ghosh · Accepted Answer · 2015-06-22T19:13:38.253

3

As far as I know the below code should not work

I'm afraid, your information is wrong.

char *string;
string = "Goo";

is perfectly valid. This is basically,

Define a char pointer string.
Put the base address of the string literal "Goo" into string.

However, instead of being a char pointer, if string would have been an array, then this would not have been possible as array's cannot be assigned (except definition time though brace enclosed list).

edited Jun 22 '15 at 19:13

answered Jun 22 '15 at 19:10

Sourav Ghosh

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2

Plus for legacy reasons, "Goo" is not `const` unless your compiler is gcc and you explicitly tell it to make them const. – Medinoc Jun 22 '15 at 19:12
1

@Medinoc ....(just for completeness), but, (attempt to) modifying them is anyway [undefined behaviour](https://en.wikipedia.org/wiki/Undefined_behavior). – Sourav Ghosh Jun 22 '15 at 19:20
1

`-Wwrite-strings` is what changes string literals to have `const char *` – o11c Jun 22 '15 at 19:28
1

@o11c Nice one, but that's maybe again `gcc` specific, IMHO, not standard `C`. Hope I'm not misunderstood. :-) – Sourav Ghosh Jun 22 '15 at 19:30
Mostly I was extending @Medinoc 's comment. But IMHO since the only standard-compliant compilers implement a significant subset of GCC extensions, GCC-specific extensions are reasonably allowed. – o11c Jun 22 '15 at 19:33
3

@o11c: It changes them to `const char[N]`, not to `const char *`. However, this is a violation of C language spec. In C string literals are not const-qualified. – AnT stands with Russia Jun 22 '15 at 19:34
"... if string would have been an array, then this would not ...". How about a _compound literal_? – too honest for this site Jun 22 '15 at 21:17
@Olaf Good Morning Sir !! Yeah, you're right, but by saying "this" , I only meant this particular assignment, in current form. :-) – Sourav Ghosh Jun 23 '15 at 06:24
Thanks for the input Sourav + others. I realise that I was confusing char* with char x[]! – user3902889 Jun 23 '15 at 08:38
@user3902889 You're welcome . :-) BTW, you can consider [accepting](http://meta.stackexchange.com/q/5234) an answer that helped you. – Sourav Ghosh Jun 23 '15 at 09:03
(Good day to you, too Sir) Ok, I think I got your point. Yes a simple assignment is not possible, you would need `memcpy()` then. – too honest for this site Jun 23 '15 at 10:20
@AnT: You are right, this is non-standard. That is a gcc-specific warning/modifier (it should not start with `-W` actually. It is not included in `-Wall` for that reason. However, as for embedded systems one very likely wants to pack string literals into Flash, this is a very welcome feature. It also warns if breaking const-correctness by assigning such a literal to a non-`const char *. – too honest for this site Jun 23 '15 at 10:27
@SouravGhosh, done! I'm still getting used to this whole stackexchange thing. Thanks for your help! – user3902889 Jun 24 '15 at 04:48

Unexpected C string definition behaviour

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