add watch shows undefined identifier visual studio 2012, cpp

Question

I encounter the strangest behavior in VS 2012 (I'm writing in cpp).

I click "add watch" on a variable and it says "identifier is undefined".

Here's an example of the code:

for (int j=0;j<32;j++)
        {
            unsigned char curValue=desc1.at<unsigned char>(0,j);
            printf("%s\n",curValue);    
        }

I had to use printf to show the value of curValue. lol.

Has anyone encountered such behavior?

Edit: more strange this occur. When debugging the following code:

    int b1[8];

    for (int k=0;k<7;k++)
        b1[k]=0;

    char q=curValue; 
    int t=0;
    while (q!=0){
        b1[t++]=q%2;
        q=q/2;
    }

The debugger just skips the loop with b1[k]=0;

Please note curValue is undefined even inside the loop.

Thanks!

Answer 1

As Joachim said: curValue is defined inside the loop. If watch window in visual studio see it as undefined value then you should turn off Compiler optimization.

Compiler optimization default is /O2 optimize for speed. To turn it off :

• Go to project, right click and choose properties
• Configuration Properties->C/C++->Optimization
• select optimization , and change it from Maximize Speed (/O2) to Disabled (/Od)