error: pasting "operator" and "+" does not give a valid preprocessing token

Question

I'm writing a small Float class in order to compare floats more easily(as we know, because of the float's precision). So I need to reload almost all operators that double has. I find there is too much repeats, such as operator+, operator-, operator* and operator/. They are similar. So I used a macro to reduce the code length. But when I complie it, it doesn't work. The error is: ``` happy.cc:24:1: error: pasting "operator" and "+" does not give a valid preprocessing token happy.cc:25:1: error: pasting "operator" and "-" does not give a valid preprocessing token happy.cc:26:1: error: pasting "operator" and "*" does not give a valid preprocessing token happy.cc:27:1: error: pasting "operator" and "/" does not give a valid preprocessing token ``` Here is my code: ``` struct Float { typedef double size_type; static const size_type EPS = 1e-8; private: size_type x; public: Float(const size_type value = .0): x(value) { } Float& operator+=(const Float& rhs) { x += rhs.x; return *this; } Floa…

Accepted Answer

`##` concatenates tokens to produce a single token; the result must be a valid single token. You don't need to do this for `operator`, as e.g. `operator+` is not actually a single token.

```
#define ADD_ARITHMETIC_OPERATOR(x) \
inline const Float operator x(const Float& lhs, const Float& rhs)\
{\
  Float result(lhs);\
  return result x##= rhs;\
}
```

Strictly speaking, you are producing a single token for the later one.

Preprocessors that are actually textual preprocessors instead of operating during tokenization, such as the one in GCC, are often lenient about this.

error: pasting "operator" and "+" does not give a valid preprocessing token

Solution

Problem