fixing lvalue quired as increment operand

Hi,

Compiler complained about the second line: error: lvalue required as increment operand

Code:

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        for (; n > 0; n--) {
            target = *((int *)lines)++;
            new_line(target);
        }

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I changed it to:

Code:

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        int *temp = (int*) lines;
        for (; n > 0; n--) {
            target = *temp;
            temp = temp+1;
            new_line(target);
        }

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Am I interpreting the sequence of operations of "target = *((int *)lines)++;" correctly?

Thanks a lot for your help!

The result of a cast in C is an r-value, but the increment must work on an l-value.

Some compilers (in some circumstances) relax this rule a little bit.
L-Value and R-Value Expressions (C)

My guess is your cast changed the size/alignment (I'm guessing lines isn't an int pointer/array).

If lines is a char array for example, then you've got other issues to deal with, namely alignment.
For example, if your char array begins at an odd address, and your machine can only access an int on an even address, then the result of your code will be an alignment exception.

Read the for loop syntax first from here

Quote:

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Originally Posted by Mr.777

Read the for loop syntax first from here

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There's nothing wrong with the loop syntax. You can omit any of the pieces of the for loop you wish to. They are all optional.


Quzah.

So what's the initial value of n then???

That's what i meant to recommend him/her to see syntax as initialization of variable is must with some value....

Quote:

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So what's the initial value of n then???

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It's whatever the previous value. ;)

Quote:

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That's what i meant to recommend him/her to see syntax as initialization of variable is must with some value....

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Not necessarily.

say if i have

Code:

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n = 0;
while( ... ) {
  n = ...
}
if( something ) {  // continue use n
  for(; n > 0 ;n-- ) {
}
}

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Huh......
Okay, think that, n is only declared but not initialized, then what?
Do you really think, his program will work fine?
And rather fighting with each other, concentrate to solve his/her problem....:-)
Peace out..

Quote:

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Okay, think that, n is only declared but not initialized, then what?
Do you really think, his program will work fine?

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We don't know whether it's init or not.
Anyway OP question has nothing to do with it.

Well the OP was asking about cast expressions and l-values, not the finer points on the use of a for loop.

If you're still stuck on for loops, perhaps start your own thread.

sorry to cause confusion. I didn't show the complete code. n is predefined. lines is void*.

yes, I want to make sure that I am interpreting the lvalue rvalue stuff correctly. The loop is irrelevant to the discussion. Thanks.

Quote:

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Originally Posted by Salem

Well the OP was asking about cast expressions and l-values, not the finer points on the use of a for loop.

If you're still stuck on for loops, perhaps start your own thread.

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