Thursday, June 18, 2009

Some Refactoring Notes

Used to indent code:

find . \( -name "*.hpp" -or -name "*.cpp" \) | xargs astyle --indent=spaces=4 --brackets=block --indent-labels --pad=oper --one-line=keep-statements --convert-tabs --indent-preprocessor

Generating Code::Blocks Project using Cmake:

cmake -G "CodeBlocks - Unix Makefiles" ..

Regular Expressions used during refactoring using Code::Blocks:

search replace

utility::shared_ptr<([\w ]*)> \1\&

What Sucked

There is no machine learning in the editors. Therefore, every task has become repetitive.

Wednesday, June 17, 2009

Understanding boost::ptr_container

Pointer containers are exception-safe container of pointers. Using them can be slightly frustrating for the users of the standard library containers, because the interface of ptr_containers are slightly different from that of standard library containers.

For example, you would probably expect from a vector of pointers to return a pointer when you perform indirection:

std::vector v;
int* p = v[i]; // ok

But ptr_vector returns a reference:

std::vector v;
int* p = v[i] ; // error: does not compile
int& p = v[i]; // ok

But the interface of ptr_vector is suited to work with algorithms:

find(v.begin(), v.end(), 3); // works only with ptr_vector

Transform Iterators

The transform_iterator can used with maps to traverse over just the keys or just the values contained in the map. An adaptor can be written to convert a usual iterator of a map into an iterator that traverses only over the value. This adaptor would have to be rewritten for ptr_map and its relatives because of its different interface.

Erasing An Element Using auto_type

typedef boost::ptr_set S;
S s;
int* j = new int(3);
s.insert(new int(5));
s.insert(new int(7));
S::iterator it = s.find(3);
std::cout << *j << std::endl; // produces 0xfeeefeee using VS

If the second last line is changed to

S::auto_type r =s.release(it);

the correct value 3 is printed. r acts just like auto_ptr: it holds a reference to the object and thus prevents it from destruction. The user has the responsibility to destroy r when the object is no longer needed. r can also be dereferenced:

std::cout << *r << std::endl; // prints 3

and the pointer can be released using r.release().

Known Issues

Currently, you also cannot store a pointer to a const inside the ptr_container.

Comparison with std container of pointers


Comparison with std container of shared pointers



The different interface of ptr_containers can be frustrating for new users but hopefully not so much after reading this article. The newer interface makes clear that the ptr_container has exclusive ownership and thus reduces bugs when compared to using a standard container of pointers.

Wednesday, June 10, 2009

Latex Image

Useful converter of jpeg to eps (the converted eps can be used with graphicx package):

jpeg2ps -h -r 600 image.jpg > image.eps