Boolean expression evaluating to false, should be true.

Hello,

I am running into a very peculiar problem. Here's a code snippet:

Code:

---

for( int i = 0; ( ( mStageInstrCounter[WB_STAGE] <= mCodeList.size() ) || ( i < mCodeList.size() ) ); i++ )
{
//code here
}

---

mStageInstrCounter is a vector of 8 ints.
WB_STAGE is a constant equal to 7.
mCodeList.size() is equal to 3 (in my sample case).

Now, this part:

Code:

---

(mStageInstrCounter[WB_STAGE] <= mCodeList.size())

---

Keeps evaluating to false. I have run this thing through my debugger and mCodeList.size() is indeed 3. In addition mStageInstrCounter[WB_STAGE] is equal to -1 (it is what each of the values in the vector get initialized to. I am trying to figure out why this is the case.

It functions as expected if I create two new ints. Assign one the value of mStageInstrCounter[WB_STAGE] and another to hold mCodeList.size(). This seems like a hackish way of doing things here. Thanks for any explanation.

Your problem is that mCodeList.size() is an unsigned value. When an unsigned value is compared to a signed value, the comparison is done as if both values are unsigned. (Your compiler should issue a warning about signed/unsigned mismatches. Do not ignore compiler warnings.)

Basically, this means that -1 is being interpreted as 2^32-1, which is the unsigned interpretation of the same bit pattern (assuming a 32-bit integer size).

One solution would be to compare to static_cast<int>(mCodeList.size()).

Oh. Well, that makes sense. It was definitely peculiar going through this with the debugger and not realizing that. I think I am just going to define a new variable called mCodeSize and set it equal to mCodeList.size(). Will solve this problem. Thanks for the info.

Quote:

---

Originally Posted by Alterah

Oh. Well, that makes sense. It was definitely peculiar going through this with the debugger and not realizing that. I think I am just going to define a new variable called mCodeSize and set it equal to mCodeList.size(). Will solve this problem. Thanks for the info.

---

Didn't your compiler give a warning that you are using signed/unsigned variables in a potentially unsafe manner?

Regards,

Paul McKenzie

Quote:

---

Originally Posted by Paul McKenzie

Didn't your compiler give a warning that you are using signed/unsigned variables in a potentially unsafe manner?

Regards,

Paul McKenzie

---

After looking at the output it did. I was working on my laptop and in order to maximize my screen space I closed out the log section of my IDE. It's been a long day.

Quote:

---

Originally Posted by Alterah

Code:

---

for( int i = 0; ( ( mStageInstrCounter[WB_STAGE] <= mCodeList.size() ) || ( i < mCodeList.size() ) ); i++ )
{
//code here
}

---

---

What's with the superfluous parens?

This is all you need.

Code:

---

for( int i = 0;  mStageInstrCounter[WB_STAGE] <= mCodeList.size()  ||  i < mCodeList.size(); i++ )

---

To me, it's easier to read when you don't add stuff that doesn't need to be there.

Quote:

---

Originally Posted by GCDEF

To me, it's easier to read when you don't add stuff that doesn't need to be there.

---

Only to a certain extent. If you're relying on a complete knowledge of the order of operations beyond what the average coder might know by heart (which takes precedence----right-shift or bitwise and?), a pair of technically superfluous parens might still be helpful.

Quote:

---

Originally Posted by Lindley

Only to a certain extent. If you're relying on a complete knowledge of the order of operations beyond what the average coder might know by heart (which takes precedence----right-shift or bitwise and?), a pair of technically superfluous parens might still be helpful.

---

That's not the case here though. When I was looking at the code it just added clutter and confusion.

I've actually simplified it further:

Code:

---

for( int i = 0;  mStageInstrCounter[WB_STAGE] < mCodeSize; i++ )

---

It is ok for i to become larger than the code size (this is a Mips simulator). And, the <= was correct at one point, but after changes my vectors to be consistent, the < is correct now.