Make sure there’s no dirty picture – Have a good big picture!

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Few years back I had worked with a Japanese customer for a health care imaging project at their site. I was relatively new to the domain. Most of the development team was there in India.

We had some solid requirements and prototyping on some new features. I had demonstrated one of the prototypes integrated to the product which essentially play back the images aligned to the ECG cycle acquired from the cardiac patient. The feature helps the sonographer to export the data as AVI. I simply tested the feature and quickly setup the demo as we’ve already crossed the deadline. Things were working just fine. This I had already seen in the prototype earlier. Fine. I demonstrated the feature successfully and was happy about it. I requested him to to try the new feature to get more feedback from him. He happily took over the system.

He simply registered a patient, then acquired the images along with ECG. He went on reviewing the acquired images, then he exported the cycles as AVI to the patient. He quit the application and opened the patient browser if appears under the current patient. Yea it’s there. I dint feel anything bad when he registered one more patient and start the application again. (Application won’t quit, it will be residing in memory always. They simply hide the window and release the resources and keeps on waiting for commands from parent application). He did the very same procedure again. It was working I was happy again. The progress bar has been displayed again and finished the export. Then he took the patient browser once more. Surprisingly the data wasn’t there under the current patient.

As I knew the code base well, I figured out within seconds what made it to disappear the data. I told him “I’m sorry, the new patient event not handled well. The code isn’t resetting/replacing the patient ID with new one. I can fix this. It’s just one line modification” and I was about to go back to my desk to modify the source.

He stopped me and smiled and explained, “Sarath-san, are you realizing that this is a serious security issue?” I could not fully understand what he really meant with security issue.

I did not reply. He continued “For programmers, it’s a one line code modification which takes to fix this issue. But think from a customer perspective. If you went a hospital with some small chest pain and the next patient is coming with some serious cardiac problem and what if his data being exported to your ID, then the doctor gives you the wrong treatment?”

The example was perfect. I could not think of a major heart surgery because of a system/sonographer’s mistake. That was kind of eye opener. Even after all these years I still remember the story.

Most of the time, programmers are either instructed to do some part of the code without having understanding of the impact. To make and maintain better software, it is also important to understand what is the big picture. What is the real impact. Always remember the issues being found during the development time is easy to fix, once it’s delivered to the customer site, the cost will be N times more, depends on the number of customers we’ve and the cost of deploying the patches. It starts from requirement capturing to implementation. It’s responsibility of the person who captures the requirements to test/inform the major uses cases, aspect and impact of the features. On the other hand, when we’re implementing something, it’s solely our responsibility to properly understand the requirement, big picture of this requirements and the impact area. It’s equally important to do regression testing to make sure that the existing functionalities aren’t broken.

When less competent people leads these activity there’s a high chance to have the information in pockets and do not explain the requirements properly to make sure that they’ve better control over the project (trust me, there are people). But that is actually making the product and themselves worse. Also it’s developers responsibility to bug the people enough to get maximum information and clarify the requirements.

C++: Erase-Remove Idiom

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Erase-remove idiom is a common technique to eliminate the elements from a C++ STL container which satisfies a particular condition.

We can do the hand written loop to remove the elements from the container. For e.g. if you want to remove an element vector you can do something as below. (note erasing element from a C++ container within a standard for or while loop with simple iterator++ will end up undefined result)

vector::iterator it = vec.begin();
while(it != vec.end())
     if( *it == 5 )
         it = vec.erase(it); // Remove and take the return of the erase function to safely reassign
     else
         ++it;

The above code is simple as it appears, it simply iterate through the elements and find if a match there for the value then remove it from the container. And it takes back the value returned form erase where it returns the iterator of the next element. If no more elements, it will vector::end

Now, the containers will have different implementations for the same function. A map::erase return void. So it’s difficult to give a single and easy strategy for each type of containers.

remove is a handy function defined in algorthm It’s easy to get confused to know what it does and distinguish between erase. remove remove (move) the elements from the given range. Mostly push it towards the end of the container. The function returns an iterator to the location where the moved elements located within the container. It essentially won’t remove the elements as such from the container. Here is the sample demo of using remove

// remove algorithm example
#include 
using namespace std;

int main ()
{
  int data[] = {10,20,30,30,20,10,10,20};      // 10 20 30 30 20 10 10 20

  // bounds of range:
  int* pbegin = data;                          // ^
  int* pend = data+sizeof(data)/sizeof(int);   // ^                       ^

  pend = remove (pbegin, pend, 20); // 10 30 30 10 10 ?  ?  ?
                                    // ^              ^

  return 0;
}

Now this handy function has an alternative version to give a comparator function which can accept the object of the type specified for the container. Inside the function, you can make decision to remove or not by specifying in the return value. In simple words, rather giving a comparison hard coded value, we’ll give a function to make decision for us. See the documentation and example here.

Erase-Remove tequenique is accomplished in following ways.
1. Move the elements to be removed to the end with the help of remove function
2. Take the return of remove and pass to the erase function as beginning and containers::end as end.
3. Finally the contianer will contains the elements which are not satisfying the comparator function/value.

#include  // the general-purpose vector container
#include  // remove and remove_if

bool is_odd(int i) { // unary predicate returning true if and only if the argument is odd
  return i % 2;
}
bool is_even(int i) { // unary predicate returning true if and only if the argument is even
  return !is_odd(i);
}

int main() {
  using namespace std;
  int elements[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
  // create a vector that holds the numbers from 0-9.
  vector v(elements, elements + 10); 

  // use the erase-remove idiom to remove all elements with the value 5
  v.erase(remove(v.begin(), v.end(), 5), v.end()); 

  // use the erase-remove idiom to remove all odd numbers
  v.erase( remove_if(v.begin(), v.end(), is_odd), v.end() );

  // use the erase-remove idiom to remove all even numbers
  v.erase( remove_if(v.begin(), v.end(), is_even), v.end() );
}

Reference:
Erase-remove idiom

Visual Studio 2011 IDE advancements

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New Visual Studio is around the corner. Microsoft Corporate Division VC, Somasegar has given a sneak peak to new IDE features in his blog.

I find this is promising. Especially, with Visual Studio 2010, we’ve found completely revamped architecture for extending Visual Studio. On the other hand, Whole Tomato is a company, which had shown what customers really wanted out of Visual Studio. Their Visual Assist X plugin is an excellent piece of art. There are other famous guys who sells similar softwares like DevExpress. But I personally prefer VA, because it’s light weight and not leaving much confusions with cluttered interfaces like others.

Visual Studio Power Tools is another awesome free option to improve your productivity. But I believe Microsoft can do well with their IDEs. Ever since Visual Studio 2003, we’ve not gained anything better out of Microsoft IDEs. Almost 8 years, though Microsoft has introduced a bunch of technologies and language improvements especially for C#, the IDE remains a substandard for the world’s biggest developer community.

Visual Studio 2011 is a positive improvement where the art of search with regular expression integrated well with to find information quickly.

Read the full scoop here in Soma’s blog