How do you construct a std::string with an embedded null?

c++ null stdstring
Bill picture Bill · Oct 2, 2008 · Viewed 44.3k times · Source

If I want to construct a std::string with a line like:

std::string my_string("a\0b");

Where i want to have three characters in the resulting string (a, null, b), I only get one. What is the proper syntax?

Answer

Martin York picture Martin York · Oct 2, 2008

Since C++14

we have been able to create literal std::string

#include <iostream>
#include <string>

int main()
{
    using namespace std::string_literals;

    std::string s = "pl-\0-op"s;    // <- Notice the "s" at the end
                                    // This is a std::string literal not
                                    // a C-String literal.
    std::cout << s << "\n";
}

Before C++14

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

To compensate for this, you need to use the constructor that builds the string from a char array (not a C-String). This takes two parameters - a pointer to the array and a length:

std::string   x("pq\0rs");   // Two characters because input assumed to be C-String
std::string   x("pq\0rs",5); // 5 Characters as the input is now a char array with 5 characters.

Note: C++ std::string is NOT \0-terminated (as suggested in other posts). However, you can extract a pointer to an internal buffer that contains a C-String with the method c_str().

Also check out Doug T's answer below about using a vector<char>.

Also check out RiaD for a C++14 solution.

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