defining operator + for double and string data types in cpp

Question

I am trying to define operator + for string and double using the following function

string operator + (const double& b,const string a){
    return to_string(b)+a;
}

When I am doing the following operation, it works well

double c = 100.256;
string d = "if only";
cout<<c+d<<"\n";

but when i pass const char instead of string , it throws compilation error(invalid operands of types ‘double’ and ‘const char [4]’ to binary ‘operator+’)

double c = 100.256;
string test = c+"sff";

Why is implicit conversion of const char[] "sff" to string not happening?

And you better accept your double by value, and string by a const reference — Alexey S. Larionov
– Alexey S. Larionov, Commented Aug 11, 2020 at 13:35
@pm100: there is an implicit convertion from const char * to std::string. The good answer would be why it cannot be used here. — Serge Ballesta
– Serge Ballesta, Commented Aug 11, 2020 at 13:38
Try std::string operator+(const double b, std::string_view a) { return std::to_string(b) + std::string(a); } std::string test = c + "sff"s; — user10063119
– user10063119, Commented Aug 11, 2020 at 13:42

Vlad from Moscow · Accepted Answer · 2020-08-11 13:55:20Z

10

According to the C++ 17 Standard (16.3.1.2 Operators in expressions)

1 If no operand of an operator in an expression has a type that is a class or an enumeration, the operator is assumed to be a built-in operator and interpreted according to Clause 8.

In this expression

c+"sff"

(where c is a scalar value of the type double) neither operand has a class or an enumeration type and a built-in operator + for types double and const char * is not defined. The pointer arithmetic is defined when a second operand has an integer type.

edited Aug 11, 2020 at 13:55

answered Aug 11, 2020 at 13:44

Vlad from Moscow

313k27 gold badges204 silver badges358 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user10063119 Over a year ago

Can using a struct also (In addition to class, enum) allow an addition. IOW, is my answer correct? Someone DVoted but didn't tell the reason.

ChrisMM Over a year ago

@anki, a class in the C++ standard usually refers to both struct and class

Collectives™ on Stack Overflow

defining operator + for double and string data types in cpp

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related