How compiler translate postfix/prefix operators?

Question

In C++ programming language

int a=2;
a++=5;
++a=6;

From above expressions Only 2nd expression is valid . How compiler translate these expressions , so that it's able to find error: lvalue required as left operand of assignment .

I have tried following translation scheme for these expressions but it's wrong .

...
unary-expression:
    postfix-expression{
    $<info.place>$ = $<info.place>1;
}
|PLUSPLUS unary-expression{
    $<info.place>$ = $<info.place>2;
    char *temp =newTemp(); 
    genCode(temp,$<info.place>2,"+","1");
    genCode($<info.place>2,temp);
}
...
postfix-expression:
    primary-expression{
    $<info.place>$ = $<info.place>1;
}
|postfix-expression PLUSPLUS{
    $<info.place>$ = newTemp(); //Generate temporary var
    genCode($<info.place>$,$<info.place>1); //Assign temp with a 
    genCode($<info.place>1,$<info.place>$,"+","1");//Increment a by 1 
}
...

When i use a++=5 then it generates

0000 : T0   =   a
0001 : a    =   T0  +   1
0002 : T1   =   5
0003 : T0   =   T1

What are the changes have to be made in action so that it works like C++ .

`C` and `C++` are different languages and behave differently in this aspect. You should decide with which language you're working. See here for elaboration: http://stackoverflow.com/questions/21351799/postfix-prefix-increment-l-value-and-r-value-in-c-and-c — SomeWittyUsername, Mar 27 '15 at 05:34
@icepack Thanks for the information question content has been updated. — sonus21, Mar 27 '15 at 08:06

score 1 · Answer 1 · answered Mar 27 '15 at 05:39

How compiler translate these expressions, so that it's able to find error: lvalue required as left operand of assignment .

It doesn't translate the first expression. It gives a semantic error instead. Showing us what code you've generated and how you did it is futile. There isn't any correct generated code for this.

And in fact these productions themselves are irrelevant. You need to add a semantic check in the assignment production to ensure the LHS is an lvalue, and print an error if it isn't.

I can't see any relevant update. You're still showing code generation from the wrong productions. I'm wondering if you have understood one word of my answer. — user207421, Mar 27 '15 at 08:43

How compiler translate postfix/prefix operators?

1 Answers1