std::getline(std::cin, nombreDelObjetoString);

std::vector<char> cData;
const char *lpbyData = "aisjiajisfj\0buenas";
size_t uNumCharacters = 19;
 
cData.reserve(uNumCharacters);
 
for(int i = 0; i < uNumCharacters; i++) {
    cData[i] = lpbyData[i];
}

int compare (const string& str) const noexcept;
int compare (size_t pos, size_t len, const string& str) const;
int compare (size_t pos, size_t len, const string& str, size_t subpos, size_t sublen) const;
int compare (const char* s) const;
int compare (size_t pos, size_t len, const char* s) const;
int compare (size_t pos, size_t len, const char* s, size_t n) const;

int compare (const char* s) const;
int compare (size_t pos, size_t len, const char* s) const;
int compare (size_t pos, size_t len, const char* s, size_t n) const;

str
Another string object, used entirely (or partially) as the comparing string.
pos
Position of the first character in the compared string.
If this is greater than the string length, it throws out_of_range.
Note: The first character is denoted by a value of 0 (not 1).
len
Length of compared string (if the string is shorter, as many characters as possible).
A value of string::npos indicates all characters until the end of the string.
subpos, sublen
Same as pos and len above, but for the comparing string.
s
Pointer to an array of characters.
If argument n is specified (4), the first n characters in the array are used as the comparing string.
Otherwise (3), a null-terminated sequence is expected: the length of the sequence with the characters to use as comparing string is determined by the first occurrence of a null character.
n
Number of characters to compare.

char *PalabraAdivinarChar = new char[PalabraAdivinar.size()];

PalabraAdivinarChar = PalabraAdivinar;

const char *PalabraAdivinarChar = PalabraAdivinar.c_str();

std::string cString;
char *lpbyData = "aisjiajisfj\0buenas";
size_t nNumCharacters = 19; // No contamos el carácter nulo del final
 
for(size_t i = 0; i < nNumCharacters; i++ {
    if(lpbyData[i] == '\0')
        lpbyData[i] = '~'; // Pon el carácter de tu elección
}
 
cString = lpbyData;

if(std::cin.fail()) {
    std::cin.clear(); 
    /*Comunicas que ya has verificado los errores. A partir de esta linea es como si no
    hubieran ocurrido, aunque en un futuro es posible que ocurran mas*/
 
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
 
    /*Si el parametro vale exactamente std::numeric_limits<std::streamsize>::max(),
    entonces se ignora todo hasta el caracter fin de línea*/
}

do {
    std::cout << "N\243mero de letras de la palabra: ";
 
    if(std::cin.fail()) { // Comprobamos si hay errores de entrada
        std::cin.clear();
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // Limpiamos el buffer manejado por la clase std::cin
    }
 
    std::cin >> nNumLetters;
} while(std::cin.fail());