c++nullstdstring

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


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?


Solution

  • 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.