Use a C-style string as a String object reference parameter

• The string class defines a char*-to-string conversion function, which allows a C-style string to be used to initialize a string object.
• One of the parameters of a parameter of type const reference indicates that: Assuming that the argument type of the argument does not match the reference parameter, but can be converted to a reference type, the program creates a temporary variable of the correct type, initializes it with the converted argument value, and passes a reference to the temporary variable.
  
  From the above two properties we know: If the formal parameter type is const string &, when the function is called, the argument used can be a string object or a C-style string, such as a string literal enclosed in quotation marks, a char array ending with a null character, or a pointer variable pointing to char.
• The above refers to a property where the const reference is a formal parameter, that is, if the referenced parameter is const, the compiler generates temporary variables in some cases, such as the following two cases:
  1, the argument type is incorrect, but can be converted to the correct type.
  2, the argument type is correct, but not an lvalue.

• Let's look at the code example.
  

  1#include <iostream>2#include <string>3  4  using namespacestd;5  6  stringVersionstring&a,Const string&b);7  8  intMainvoid)9  {Ten      stringinput ="I Love you.";  Onecout <<"Input Address:"<< &input <<Endl; A      Const Char* B ="***"; -cout <<"I b Address:"<< &b <<Endl; -   the version (input, b); -   -      return 0; -  } +   -  stringVersionstring&a,Const string&b) +  { A      using namespacestd; atcout <<"a address:"<< &a <<Endl; -cout <<"Address B:"<< &b <<Endl; -      returnA//without this, a memory error is generated. Returns a reference.  -  } -  /************************************ - * Input address:0x7ffe09a647f0 in * I b address:0x7ffe09a647e8 - * a address:0x7ffe09a647f0 to * b address:0x7ffe09a64840 +   * **********************************/

  where input is a string object, the string class is applied to define a char*-to-string conversion function that converts the string literal to a string object. B is the char* type, and as an argument the function creates a temporary variable. Looking at the code, the address of B in main is:I b address:0x7ffe09a647e8 , and the address in version is:b address:0x7ffe09a64840 . They are different, stating that the function is not a reference to passing a char *b, but a temporary variable. Also see the string class input, in main and in version address is the same. The description is a reference that passed input.
  

Use a C-style string as a String object reference parameter