How do I validate an empty string?

To find out if an object of type std::stringis empty, you have several options at your disposal:

• length: This method returns the number of characters. If the object is empty the length will be zero:

  std::string test = /* ... */
  if( test.length() == 0 )
    std::cout << "Cadena vacia";
  

• size: This method is equivalent to length. The existence of sizeis justified so that std::stringit can be used with container functions ( std::vector, std::set, etc...)

• empty: This method returns a boolean indicating whether the object is empty or not... plain and simple it does exactly what you ask.

  if( test.empty() )
    std::cout << "Cadena vacia";
  

• Iterators: Okay, it's not the most orthodox way to do it, but for that matter, it's a different way of verifying that the string is empty:

  if( test.begin() == test.end() )
    std::cout << "Cadena vacia";
  

The easiest way to do it is Elnombredetustring.empty()by putting it ifin some example:

if(Elnombredetustring.empty())
{
  cout<<"Esta vacio"
}

And with your question why the way you try to do it doesn't work is because for it to work as you show:

while (nombre[0] !='\0'){
        cout<<nombre<<endl;
        cout<<"ingrese una palabra "; cin>>nombre;
    }

It means that the name has a value of 0, not that it is null, that is, you would have to match the string to the char of 0, but that does not mean that it is empty.

You can try with TextIsEmpty,

int main(){
    string nombre;
    cout<<"ingrese una palabra "; cin>>nombre;
    while (nombre.TextIsEmpty()){
        cout<<nombre<<endl;
        cout<<"ingrese una palabra "; cin>>nombre;
    }
}

or put it with a defined value that would be zero

   int main(){
        string nombre;
        cout<<"ingrese una palabra "; cin>>nombre;
        while (strlen(nombre) == 0){
            cout<<nombre<<endl;
            cout<<"ingrese una palabra "; cin>>nombre;
        }
    }

My problem is in the condition while (nombre[0] !='\0')that apparently does not read it for some reason.

You're in trouble if you rely on that condition.

If the std::stringis empty it will have no elements, no elements. So by accessing the first element of a std::stringvoid you are causing undefined behavior . So it could get stuck in a loop and never exit , or it could throw a runtime error, or daemons could be spawned out of your nostrils .

The value is read, but we described in the previous paragraph it will be an indeterminate value that is possibly almost never '\0'and therefore almost never exits the loop even though it std::stringis effectively empty.

Having described the problem you are facing, let's move on to the solutions. If we consult the documentationstd::string we see that it has several functions related to its capacity:

• empty: Check if the string is empty.
• size, length: Returns the number of characters stored.
• max_size: Returns the maximum number of characters the string can store without exceeding library or implementation limits.
• reserve: Reserve memory to store more characters.
• capacity: Returns the memory reserved for this string, whether it contains data or not.
• shrink_to_fit: Reduces the memory reserved by the chain so that it is equal to the memory that contains data.

sizeIn your case only the , lengthand functions are relevant empty, which you could use as follows:

while (nombre.size()){
    cout<<nombre<<endl;
    cout<<"ingrese una palabra "; cin>>nombre;
}

Integer values ​​are implicitly convertible to boolean condition being a value 0interpreted as falseand any other value interpreted as true; so: if it sizereturns a value other than 0, it will stay in the loop, exactly the same thing happens with:

while (nombre.length()){
    cout<<nombre<<endl;
    cout<<"ingrese una palabra "; cin>>nombre;
}

Finally, we can tell if it's empty with the function as well empty, but it requires us to reverse the check (since we want the loop to continue as long as it's not empty):

while (!nombre.empty()){
    cout<<nombre<<endl;
    cout<<"ingrese una palabra "; cin>>nombre;
}

You can try putting nombre.IsEmpty()in the if which returns true or false depending on whether the string is empty or not. You can also try using strlen(nombre) == 0, what strlen does is count the number of indices of the string (or the length of the string). I hope it helps you.