CODEWITHSUNDEEP
coperatorsc-preprocessoroperator-keyword
Brian Tracy
Brian Tracy

Reputation: 6831

Redefinition of Assignment Operator

It is in my understanding that several languages use := as the assignment operator. This is implemented to possibly avoid any confusion with the == operator. This seemed like a very valid point to me, so I was thinking of how to implement it in a language like C. Here is what I was thinking.

#define := =
// ... later on

int x := 4;

Although this would work (if the preprocessor supported that syntax), it would still allow me to get away with using the = operator. So my question is, Is there a way to "flag" a symbol or operator / Is there a way to prevent the use of some defined operator or symbol? Again, here is what I was thinking, but I don't know about the syntactical / semantical legality of this.

#undef =

Upvotes: 1

Views: 146

Answers (3)

Keith Thompson
Keith Thompson

Reputation: 263657

#define := =

A macro name can only be an identifier. I'd be quite surprised if any C compiler accepted that definition. In principle, a compiler could accept it as a language extension, but gcc, for example, does not. Any conforming C compiler must at least issue a diagnostic.

You say it works; I'm frankly skeptical. What compiler are you using?

#undef =

Same problem.

I can see (and even agree with) your point that using := rather than = for the assignment operator would have been a better idea. But using the preprocessor to alter the language like this, even in cases where it works, is rarely a good idea.

C programmers know that = means assignment. Anyone reading your code can probably guess that := is meant to be assignment, but it would just make your code that much harder to read.

Upvotes: 1

YaleCheung
YaleCheung

Reputation: 630

Good question, but don't do that. Your method results in bad readability.

Upvotes: 1

Mahonri Moriancumer
Mahonri Moriancumer

Reputation: 6013

Standard C does not allow the '=' assignment operator to be undefined, or changed. However, the source code to several C compilers is available; and you are welcome to make your own modifications to your build of a C compiler. Including changing '=' to ':='. Good luck!

Upvotes: 1

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