CODEWITHSUNDEEP
cgccsyntax
Dervin Thunk
Dervin Thunk

Reputation: 20119

Evaluation on the right side of an assignment

This int c = (a==b) is exactly what I'd like to say in my C program, compiling with GCC. I can do it, obviously (it works just fine), but I don't know whether it may cause undefined behavior. My program will not be compiled with some other compiler or in other architectures. Is this legal ANSI C? Thanks.

Upvotes: 1

Views: 113

Answers (4)

ouah
ouah

Reputation: 145829

It is perfectly valid if c is declared at block scope.

When declared at file scope it is not valid because the initializer has to be a constant expression.

a == b is an expression and in that sense is not different that another expression like a + b or a & b.

Upvotes: 1

Luchian Grigore
Luchian Grigore

Reputation: 258568

Well, it depends on what the types of a and b are. If they are types that support equality check, then yes, it's perfectly legal.

Upvotes: 0

kennytm
kennytm

Reputation: 523254

int c = (a == b);

this is perfectly legal. Initialization is part of the C standard (C99 §6.7.8), the right hand side can just be any assignment-expression, including a == b (of course, assuming a and b are defined and have comparable type).

Upvotes: 1

asaelr
asaelr

Reputation: 5456

It's completely legal. if a is equal to b, then c will be 1. else, it will be 0.

Upvotes: 4

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