null character inside string

Question

From Rules for C++ string literals escape character ,Eli's answer

std::string ("0\0" "0", 3)  // String concatenation

works because this version of the constructor takes a char array; if you try to just pass "0\0" "0" as a const char*, it will treat it as a C string and only copy everything up until the null character.

Does that mean space isn't alloted for entire string , ie the string after \0 is written on unalloted space ?

Moreover the above question is for c++ string, I observed same behaviour for c strings too . Are c and c++ strings same when I add null char in middle of string during declaration ?

What are you trying to do here: Why do you need to use strings instead of just character arrays? — hugomg, Jul 28 '13 at 08:34
There is a set of strings which could be represented as a array of pointers to char[] , but is represented as char[] with \0 separating strings and int[] to store offsets of strings — Zxcv Mnb, Jul 28 '13 at 08:41

Oswald · Answer 1 · 2013-07-28T08:41:26.767

2

The char array is copied into the new object. If you don't specify, how long the char array is, C++ will copy until the first null character. How much additional space is allocated is outside the scope of the specification. Like vectors, strings have a capacity that can exceed the amount required to store the string and allows to append characters without relocating the string.

edited Jul 28 '13 at 08:41

answered Jul 28 '13 at 08:34

Oswald

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so something like char w[]="qwe\0""0uqwe"; printf("%s\n%s",w,w+4); is wrong ? – Zxcv Mnb Jul 28 '13 at 08:36
`char w[]="qwe\0""0uqwe"` casts a `const char*` to `char[]`. That's wrong. – Oswald Jul 28 '13 at 08:39
1

The string capacity isn't *completely* outside the scope of the spec: you're guaranteed that capacity >= size. – Casey Jul 28 '13 at 08:41
"How much *additional* space is ...". Better? – Oswald Jul 28 '13 at 08:43
So is size here size of "qwe" or size of "qwe\0""0uqwe" ? – Zxcv Mnb Jul 28 '13 at 08:44
What does `sizeof("qwe\0""0uqwe")` tell you? What does `strlen("qwe\0""0uqwe")` tell you? – Oswald Jul 28 '13 at 08:49
strlen considers string only till \0 , while sizeof considers entire array – Zxcv Mnb Jul 28 '13 at 09:11

P0W · Answer 2 · 2013-07-28T08:55:51.157

std::string constructor that takes a const char* assumes the input is a C string. C strings are '\0' terminated and thus stops when it reaches the '\0' character.

If you really want to play you need to use the constructor that builds the string from a char array (not a C-String).

STL sequence containers exceed the amount required to store automatically

Example :

int main () {

string s="Elephant";

s[4] ='\0'; //C++ std::string is NOT '\0' terminated
cout<<s<<endl; //Elep ant

string   x("xy\0ab");   // C-String assumed.

cout<<x; //xy
  return 0;
}

null character inside string

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