Assertion: Great Practice for Software Development

In this post, I will discuss recommended usage of assertion in programming. For both C/C++/Java, assert is a great way to alert a programmer that there is something against his expectation.

Let's do a quick example. Say you are implementing quick sort. In particular, you are trying to validate your partition method. You can insert an assertion to make sure that your partition method is functioning as expected, as below:

	#include <assert.h>
	#include <vector>
	using namespace std;
	// check if partitioned array[start:pivot] and array[pivot+1:end]
	bool isPartitioned(vector<int>& array, int start, int pivot, int end) {
	for (int i=start; i<pivot; i++)
	if (array[i] > array[pivot]) return false;
	for (int i=pivot+1; i<end; i++)
	if (array[i] <= array[pivot]) return false;
	return true;
	}
	// partition array[start:end]
	int partition(vector<int>& array, int start, int end) {
	int pivot = start;
	int i = start+1;
	int j = end - 1;
	while (true) {
	while (i < j && array[i] <= array[pivot]) i++;
	while (array[j] > array[pivot]) j--;
	if (i >= j) break;
	swap(array, i, j);
	}
	swap(array, j, start);
	assert(isPartitioned(array, start, j, end));
	return j;
	}

view raw partition.cpp hosted with ❤ by GitHub

Well, you must agree that assertion is a very great tool for debugging, as it tells you exactly where it could have gone wrong. Unfortunately, assertion will slow down the performance and is not needed for production code, so do we need to comment them out when releasing the code for production?

In fact, both C/C++ and Java has a nice way to disable and enable the entire assertion statements. For C/C++, you simply need to define a macro NDEBUG, which will disable all assertions. Otherwise, assertions are enabled by default, unless of course you define NDEBUG macro in your source files explicitly. Therefore, you need disable assertions at compile time for production binary:

$ g++ *.cpp -DNDEBUG

Here, -D is the option for implicit #define macro, so the option -DNDEBUG will define NDEBUG macro for all files.

For Java, there is -da and -ea options which will disable and enable assertions, respectively at the runtime. In fact, assertions are by default disabled in Java, so you need to enable with -ea option when debugging, as below:

$ java -ea SomeClass

For more info, please refer to this and this official documentations.

Happy coding!