How have null value inside basic_string in c++

Question

Is there a way to have and process null value inside std::basic_string?

Sometimes the string sequence being passed has null values. For example below code outputs 1234,5678 instead of whole string.

#include <iostream>
#include <string>
#include <cstring>
int main ()
{
   int length;
   std::string str = "1234,5678\000,ABCD,EFG#";
   std::cout << "length"<<str.c_str();
}

I need to get the complete string.

@Manwal That would be the c_str() member function of the standard C++ string class. What does it look like? — Sebastian Redl
– Sebastian Redl, Commented Nov 19, 2014 at 12:41

Mike Seymour · Accepted Answer · 2014-11-19 14:05:32Z

6

First, you'll have to tell the string constructor the size; it can only determine the size if the input is null-terminated. Something like this would work:

std::string str("1234,5678\000,ABCD,EFG#", sizeof("1234,5678\000,ABCD,EFG#")-1);

There's no particularly nice way to avoid the duplication; you could declare a local array

char c_str[] = "1234,5678\000,ABCD,EFG#"; // In C++11, perhaps 'auto const & c_str = "...";'
std::string str(c_str, sizeof(c_str)-1);

which might have a run-time cost; or you could use a macro; or you could build the string in pieces

std::string str = "1234,5678";
str += '\0';
str += ",ABCD,EFG#";

Finally, stream the string itself (for which the size is known) rather than extracting a c-string pointer (for which the size will be determined by looking for a null terminator):

std::cout << "length" << str;

UPDATE: as pointed out in the comments, C++14 adds a suffix for basic_string literals:

std::string str = "1234,5678\000,ABCD,EFG#"s;
                                           ^

which, by my reading of the draft standard, should work even if there is an embedded null character.

edited Nov 19, 2014 at 14:05

answered Nov 19, 2014 at 12:47

Mike Seymour

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4 Comments

user657267 Over a year ago

There's also the basic_string literal suffix s in C++14, the latest libc++ and libstdc++ both support it.

Mike Seymour Over a year ago

@user657267: Thanks, I'm not yet familiar with C++14. Do you know whether it works if there's a null character in the literal string?

Mike Seymour Over a year ago

@user657267: I guess it does, since the operator is passed the length of the literal.

user657267 Over a year ago

I believe so, can't say I've actually used it yet and for some reason gcc 4.9.1 isn't finding it...should work in theory though.

Jonathan Mee · Accepted Answer · 2014-11-19 13:40:29Z

1

You can do this with std::string(std::initalizer_list<char> il) it's just a little bit of a pain in the neck:

string str{'1', '2', '3', '4', ',', '5', '6', '7', '8', '\0', '0', '0', ',', 'A', 'B', 'C', 'D', ',', 'E', 'F', 'G', '#'};
cout << "length: " << str.size() << ": " << str;

Outputs:

length: 22: 1234,567800,ABCD,EFG#

answered Nov 19, 2014 at 13:40

Jonathan Mee

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