Gdcm coding style (and other religious/agnostic beliefs)
* Introduction:
The following coding style intends to ease the work of developpers
themselves but also of users who will study, maintain, fix, and extend
the code. Any bread crumbs that you can drop in the way of explanatory
names and comments will go a long way towards helping other readers and
developers.
Keep in mind that to a large extent the structure of code directly
expresses its implementation.
* Language:
- C++ (for the kernel) and Python (for the wrappers).
- all the names (variables, members, methods, functions) and comments
should be based on English. Documentation, guides, web site and other
informations should be in English.
Make sure you use correct (basic) English and complete, grammatically
correct sentences for comments and documentation.
* General layout:
- Each line of code should take no more than 79 characters. Break the code
across multiple lines as necessary.
- Methods and functions should keep a reasonable number of lines when
possible (a typical editor displays 50 lines). Avoid code duplication.
Always prefer creating a new method or function to duplication.
A high indentation level generally suggests the need for a new
method or function.
- All the code should be properly indented. The appropriate indentation
level is three spaces for each level of indentation. DO NOT USE TABS.
Set up your editor to insert spaces. Using tabs may look good in your
editor but will wreak havoc in others, or in external tools (e.g. side
by side diffs).
- The declaration of variables within classes, methods, and functions
should be one declaration per line. Provide them with default values
and don't rely on compilers for default initialization.
* Naming conventions:
- Generalities:
In general, names are constructed by using case change to indicate
separate words, as in ImageDataSize (standing for "image data size").
Underscores are not used. Variable names are choosen carefully with the
intention to convey the meaning behind the code. Names are generally
spelled out; use of abbreviations is discouraged.
[Note: abbreviation are allowable when in common use, and should be in
uppercase as in LUT or RGBA.]
While this does result in long names, it self-documents the code.
- Naming Files:
Files should have the same name as the class, with a "gdcm" prepended.
Header files are named .h, while implementation files are named either
.cxx or .txx, depending on whether they are implementations of templated
classes. For example, the class gdcm::Document is declared and defined
in the files gdcmDocument.h and gdcmDocument.cxx.
- Naming Class Data Members, Methods, and Functions:
Class data members are named beginning with a capital letter as in
GroupPixel.
Global functions and class methods, either static or class members, are
named beginning with a capital letter, as in GetImageDataSize().
- Naming Local Variables:
Local variables begin in lowercase. There is more flexibility in the
naming of local variables although they still should convey some
semantics.
- Naming function parameters:
Function parameters begin in lowercase. There is more flexibility in the
naming of function parameters although they still should convey some
semantics.
* Classes:
- Don't use the inline keyword when defining an inline function
within a class definition.
- As stated in the "Naming conventions" section, class data members
are named beginning with a capital letter as in GroupPixel.
But the parameter names of method should be named with a lowercase
letter (in order to distinguish at a glance data members, from parameters
and also to avoid potential collisions with data members):
void A::SetGroupPixel( int groupPixel )
{
GroupPixel = groupPixel;
}
- Don't use trailing ';' in inline function definition.
use :
void A::SetGroupPixel( int groupPixel ){GroupPixel = groupPixel;}
NOT
void A::SetGroupPixel( int groupPixel ){GroupPixel = groupPixel;};
- Do not repeat the virtual keyword when overriding virtual base methods
in declaration of subclasses:
class A
{
virtual void foo(...);
};
class B: public A
{
void foo(...); // and not: virtual void foo(...);
};
- The public, protected, private declarations should be at the
same indent level as the class. Use
class A
{
private:
void foo(...);
public:
void bar(...);
};
- Method and functions devoided of arguments should not use the void
notation. Use
SomeType Header::GetPixelData()
and not
SomeType Header::GetPixelData(void).
* Use of braces:
- Braces must be used to delimit the scope of an if, for, while, switch, or
other control structure. Braces are placed on a line by themselves, and
at the same indentation level as the control structure to which they
belong:
for (i=0; * i<3; i++)
{
...
}
or when using an if:
if ( condition )
{
...
}
else if ( other condition )
{
...
}
else
{
....
}
You can choose to use braces on a line with a code block when
the block consists of a single line:
if ( condition ) { foo=1; }
else if ( condition2 ) { foo=3; }
else { return; }
or
for (i=0; i<3; ++i) {x[i]=0.0;}
Methods and functions should follow the same usage of braces:
void File::ParsePixelData()
{
...
}
* Special layout:
- Avoid code mixed with comments on a single line. Instead, prepend the
logical blocks of code with the concerned comments.
- Use parentheses around conditions e.g. with an if statement:
if ( someLocalVariable == 2 ) { ... }
- Add spaces around parentheses, or braces. Use
if ( someLocalVariable == 2 ) { ClassMember += 1; }
and not
if (someLocalVariable == 2) {ClassMember += 1;}
- Add spaces around each side of the assignement operator, and
around binary operators used in boolean expression. Use
someLocalVariable = ClassMember * 2;
if ( someLocalVariable == 2 || ClassMember == 2 ) ...
and not
someLocalVariable=ClassMember*2;
if ( someLocalVariable==2||ClassMember==2 ) ...
* Miscelaneous:
- Don't use underscores. Don't use tabs. Don't use control characters
like ^M. Anyhow, cvs is configured to reject such commits.
- Comments should be in C++ style ("// ...", two slashes, per line). Don't
use C style comments ("/* ... */").
- The last line of a file should terminate with "\n".
- Returned arguments of methods and functions should not be wrapped with
parentheses. Use
return iter->second;
but do not use
return ( iter->second );
* Debugging and Verbose modes:
Never use std::cout. Instead use the gdcmDebug class through the
global instance dbg. Example:
#include "gdcmDebug.h"
...
{
dbg.Verbose(3, "Local function name: entering.");
...
}
will send the message to std::cout when dbg.Debug() is called
in your main.
* Documentation:
The Doxygen open-source system is used to generate on-line documentation.
Doxygen requires the embedding of simple comments in the code which is in
turn extracted and formatted into documentation. See
http://www.stack.nl/~dimitri/doxygen/
for more information about Doxygen.
- Documenting a class:
Classes should be documented using the class and brief doxygen commands,
followed by the detailed class description:
/**
* \class Header
* \brief Header acts as container of Dicom elements of an image.
*
* Detailed description of the class is provided here
* ...
*/
The key here is that the comment starts with /**, each subsequent line has
an aligned *, and the comment block terminates with a */.
- Documenting class members and inline methods:
All the members and the inline methods should be documented within
the class declaration as shown in the following example:
class Header
{
/// True when parsing was succesfull. False otherwise.
bool Readable = false;
/// \brief The number of lines of the image as interpreted from
/// the various elements encountered at header parsing.
int NumberOfLines = -1;
/// Predicate implemented as accessor around \ref Readable.
bool IsReadable() { return Readable; }
};
- Documenting a Method:
Methods should be documented using the following comment block style
as shown in the following example:
/**
* \brief Within the Dicom Elements (parsed with the public and private
* dictionaries), look for the element value representation of
* a given tag.
* @param group Group number of the searched tag.
* @param elem Element number of the searched tag.
* @return Corresponding element value representation when it exists,
* and the string "gdcm::Unfound" otherwise.
*/
std::string Document::GetEntryByNumber(guint16 group, guint16 elem)
{
...
}
* External includes and C style:
- Only the C++ standard library and the STL includes should be used.
When including don't use the .h extension (use #include
instead of #include ).
Note: include the stl header AFTER the gdcm ones (otherwise pragma
warnings won't work).
- Don't use the C standard library. Don't include stdio.h, ctype.h...
Don't use printf(), sprinf(), FILE*...
- Don't use the NULL notation (neither as macro, nor as const int NULL=0).
A pointer that doesn't refer to an object should simply be defined as
DataPointer* MyDataPointer = 0;
* Basic types:
- Assume T is a given type. When declaring or defining with the
"pointer to T" notation, the * character must be adjacent to
the variable and not the type. That is use
T *foo = 0;
and not
T* foo = 0;
nor
T * foo = 0;
- Assume T is a given type. When declaring or defining with the
"reference to T" notation, the & character must be adjacent to
the variable and not the type. That is use :
T &foo = 0;
and not
T& foo = 0;
(Doxygen will not have any longer to correct)
- Always define a typedef for a new type and be consistent in usage.
Use
typedef Header *HeaderPointer;
HeaderPointer MyHeaderPointer;
- One notorious counter example for non using C style inclusion concerns
exact-width integers (since there seem to be no equivalent for C++).
When using exact-width integers use the typedef names defined by
the Basic ISO C99: 7.18 Integer types i.e.
int8_t int16_t int32_t int64_t (signed integers)
and
uint8_t uint16_t uint32_t uint64_t (unsigned integers).
Conversion table is then:
unsigned char -> uint8_t;
unsigned short -> uint16_t;
unsigned int -> uint32_t;
unsigned long -> uint32_t;
unsigned long long -> uint64_t;
(signed) char -> int8_t;
short -> int16_t;
int -> int32_t;
long -> int32_t;
long long -> int64_t;
Hence do not use declarations like "unsigned int".
With g++, accessing those typedef is achieved by the following
#include < stdint.h >