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The C++ language has many powerful features, but this power brings with it complexity, which in turn can make code more error-prone and harder to read and maintain. The goal of this guide is to help you manage this complexity by describing in detail the major dos and don'ts of writing C++ code for Cinema 4D plugins. We recommend you enforce consistency to keep your code base manageable. Creating common idioms and patterns makes code much easier to understand. In some cases there might be good arguments for changing certain style rules, but nonetheless it is best to preserve consistency as much as possible. A major benefit is it will allow us to better understand your code when asking for help on the Plugin Cafe forum or via direct support.
Another issue this guide addresses is that of C++ feature bloat. C++ is a huge language with many advanced features. In some cases we constrain, or even ban, the use of certain features. We do this to keep code simple and to avoid the various common errors and problems that these features can cause. This guide lists these features and explains why their use is restricted.
The following C++ 11 features are currently supported:
std::is_pod, std::is_scalar, std::is_base_of, std::is_function, std::is_polymorphic, std::is_convertible static_assert auto decltype nullptr Do not use "for" statements that use floating point values as an increment. Float increments can lead to infinite loops or unexpected behavior.
Don't use ANSI C routines in your code if there is a library replacement. E.g. memset, memcpy, printf, scanf etc. should never be touched.
Explicitly cast data with static_cast, const_cast, or reinterpret_cast. Use conversion constructors for fundamental types and avoid C-style casts due to their unsafe nature.
The goto statement should only be used if it is absolutely the best choice for an algorithm's implementation. Generally, your code should be structured so that it can return at any point and that it makes sure everything is cleaned up properly.
Do not use external libraries (e.g STL or BOOST) unless absolutely necessary.
Be aware of threading! It's recommended to stick to the following directions:
Static or global variables of class type (e.g. using something like String g_mySharedStringVariable) are forbidden due to the indeterminate order of construction and destruction. The same applies to AutoMem.
Only use the classes BaseArray, BlockArray, PointerArray or derived classes. Whenever you access arrays make sure that any access is within boundaries, otherwise you'll provoke a crash and undefined behaviour. You can only omit those checks for speed critical areas. In that case, you should document in the routine's header that a variable needs to be within a certain range.
When iterating, use references (unless specifically needed otherwise) so that no unnecessary data will be copied. Always use const if no modification is necessary. If it doesn't compile, fix your classes so they properly support constness. If you need additional functionality obtain an auto-iterator with ForEach::Get() or an erase-iterator with ForEach::EraseIterator.
Use constants instead of magic numbers wherever possible. The meaning of arbitrary numbers is often not clear to the reader. An explicit name helps readability.
Try adopting a defensive style - add additional checks, even if you are sure these conditions do not happen. At a later time, circumstances may change, making those particular conditions come true. Make sure your source code compiles free of warnings on all platforms and targets.
C++ exceptions and RTTI will not be used in any of our projects unless external libraries require it (also RTTI operators typeid and dynamic_cast cannot be used).
Every memory allocation must be checked. It is not sufficient to check and leave your scope though. You must make sure that a class is not in an uninitialized state and will still properly function according to specifications. It is highly recommended that you implement memory checks during development and not at the very end of a development cycle. Instead of using memory blocks always use arrays (e.g. BaseArray, BlockArray, PointerArray). They're much more flexible, safe (you get additional safety checks in debug builds), reduce code size and offer the same performance.
Any class allocation (except for system or library specific code) must be done using NewObj() and DeleteObj(). Any memory allocation must be done using NewMem() and DeleteMem(). Memory obtained with NewObj() and NewMem() is NOT initialized, so you must make sure that the class/struct constructors properly initialize all member variables. To obtain cleared memory, use NewMemClear(). For constructors, this is not available. As a side note, AutoMem is a convenient way to free memory when your scope is left in case of an error.
Circumventing Cinema 4D's memory management and using the standard libs allocators will result in lower speed and will keep you from utilizing Cinema 4D's leak detection utilities.
Any floating point division must be checked for 0.0 unless the algorithm specifically doesn't require this check. An example where it is not necessary is e.g. x /= (1.0 + vectorA * vectorA) where the divisor never can become 0.0. Otherwise, a test must be done. It cannot be stated often enough that floating point calculations are imprecise... (c - d below) can be different to 0.0 and then in the next code line be 0.0. This is not even uncommon with optimizing compilers. See the examples below that will always fail!
Any integer division must also be checked for 0, however the strict requirements aforementioned don't apply here.
Always be careful with type conversions as they are a frequent cause for crashes!
E.g. if you want to calculate an index within a 2-dimensional array. Let's assume both dimensions are larger than 32767 units. In that case the index needs to be of type Int (64-bit), otherwise you'd get an overflow. What is often overseen though is that it is not enough to just change the index to Int:
If you take a look in the debugger you'll see the following:
The calculation is done with Int32 and then at the end the result is casted to Int (when it is too late).
So the only correct way to write this (in case you want to keep x, y and xRes as Int32) is:
or
but not
Another frequent conversion problem is if you go from Float to Int. In many places a 3D point is projected onto the screen, converted to Int and then clipped against the screen boundaries. This will always fail!
Let's take a look why:
In the debugger you will see:
So if you want to perform a proper clipping you have two possibilities:
a) Clip floating point values first (on a float basis) and then convert to Integer
b) Use SAFEINT(32) which makes sure that if a floating-point value exceeds the minimum/maximum integer number then the minimum/maximum will be set
For Asserts and Stops there is DebugAssert() / DebugStop() as well as CriticalAssert() / CriticalStop().
Generally, any of those functions should only be used if there is (or to check for) a severe problem in your code. E.g. a DebugAssert() could check if the sum of segments matches the total count, or if a pointer is != nullptr, as anything else shouldn't (or can't) be the case. A DebugAssert() shall not be set for any conditions that are relevant only to you (e.g. stop if the name of an object is 'default') or are not critical for the algorithm (e.g. stop if a file handler can't open a file).
DebugAssert() / DebugStop() are like their Critical counterparts, but will be removed during release builds for speed reasons. If the code is speed uncritical try to utilize the Critical versions.
When outputting a value you can choose from DiagnosticOutput(), WarningOutput() and CriticalOutput(). CriticalOutput() and WarningOutput() will by default be visible to the end-user, DiagnosticOutput() needs to be manually enabled. CriticalOutput() additionally enforces a CriticalStop() compared to WarningOutput(). CriticalOutput() and WarningOutput() print header information about source code file, line and current time.
To avoid trouble on case sensitive file systems or when compiling cross-platform, the names of any source files are lowercase and cannot contain any white spaces or special characters (ASCII characters >=128).
Every *.cpp file should have an associated *.h file (unless it is e.g. a main.cpp)
All header files must be protected by define guards containing the file name in upper cases with the dot replaced by an underscore and two underscores appended.
Keep the number of code lines within a file within reason. Long files might be better grouped into smaller ones and improve readability. If your file exceeds 5000 lines it should definitely be split into parts.
Only include header files when necessary, use forward declarations of classes if possible.
Always use C4D's datatypes Int, Int32, Int64, Float, Float32, Float64, Bool, Char, etc. unless system specific code requires otherwise. You should use nullptr instead of NULL or 0.
Use true and false for boolean variables (not TRUE or FALSE, etc.).
Only use size_t when it is explicitly necessary. Otherwise, Int is the better choice, as it is signed and allows for subtractions and comparisons. Use the macro SIZEOF instead of sizeof to automatically cast to the datatype Int.
Try to use the unsigned datatypes UInt, UInt32 and UInt64 only if there is a real benefit vs. Int, Int32 and Int64.
Any index or size should be of type Int. Do expect that memory can become bigger than 2 GB. If you need to be able to specifically handle more than 2GB data on 32 bit systems (e.g. for File I/O) you must use Int64 instead of Int, as Int is defined as 32-bit on a 32-bit system and 64-bit on a 64-bit system.
Code must be commented. It makes it easier for other developers to understand what your code does, and why, thus saving lots of time later. When writing code comments, try to describe why things are done, not what is done. It is easy to find out what is done by just reading the code. But it's hard to find out the reason why things are done. Therefore, always describe the purpose of the code in your comments.
Comments that just repeat the code below are counterproductive. Even worse, often the comment will be outdated and not reflect what is happening in the code anymore. For interfaces describe valid ranges for variables, return values, special conditions and anything that is non-obvious (e.g. if a function class has a certain performance or threading behaviour, if it interacts with another portion of the code or if it needs to be called within a certain context). If functions or members have to be called in a certain order this needs to be documented (unless it is obvious e.g. in the case of Init()). Every class definition should have an accompanying comment that describes what it is for and how it should be used.
Try to make your source more readable instead of adding lots of comments. Comments do not make up for bad code. A good way to add readability is to introduce constants and assign in-between calculations to clearly named variables.
Here there is no need for any comments. The code is clear and modifications to the code don't require modifications to the comments as well.
We use a tab width of 2. Furthermore, tabs are only used at the beginning of a line and to visually align elements. Tabs should not be used after an opening parenthesis or as a replacement for a single space.
Use spaces like in your natural language. Spaces should be set after a semicolon or comma and after comparisons or assignment operators. Arithmetic calculations should be separated by a space.
Prefer small and focused functions and member routines, as this makes it easier for others to get a general idea of the algorithm and allows the compiler to create more efficient code. As a guideline routines should not get longer than two full screen pages - otherwise think how it can be split up into smaller tasks.
Opening/closing brackets should be aligned at the same X position or be within the same code line. However, be aware that placing the code in the same line makes debugging harder as you can't set a breakpoint for the execution part and won't see if the condition was met or not.
Don't introduce additional brackets if there is no need for it and if it doesn't improve readability.
Switch statements are formatted in the following way:
case statements are indented by one tab compared to the switch statement.case statements.break statement is indented by one tab compared to the case statements and is written before the closing bracket.case and break can go on the same line (but this should only be used if all cases follow the same formatting).case must stop with either MAXON_SWITCH_FALLTHROUGH, break, continue or return.If you specifically design a fallthrough for a switch statement MAXON_SWITCH_FALLTHROUGH must be used to document the code. Note that this only needs to be done if the fallthrough happens after some code was written, not for a list of multiple cases.
Don't use assignments in if statements.
Always start a new line after the if statement, as this makes debugging easier.
else statement it needs to be followed by a new line.if / else statements must use brackets.if - block has brackets, the else block must have brackets too and vice versa.if / else there always must be a new line.Do not put spaces around the period or arrow operators for pointers and classes. Pointer operators have no space after the * or the &. When declaring a pointer variable or argument, group the asterisk to the type, unless you are declaring many variables of the same type at once.
#if, #ifdef, #elif, #else, #endif statements should be aligned at horizontal position 0. If they are nested, indentation should be used. #undef should never be used unless absolutely necessary, and never goes into a header file.
Operator names need to be treated like regular function names.
Use exactly this formatting:
Use strongly typed enum constants instead of defines wherever possible. This vastly enhances source code readability. The convention is to type the enum in capital letters. List elements do not repeat the enum name.
Flags (unless they're bit arrays) must be defined as strongly typed enums. If you need a default element that equals the value 0 you should define the list element NONE. To test a flag set for a bit use CheckFlag(value, bit), e.g. CheckValue(myFlags, MOUSEDRAGFLAG::NOMOVE). Do not cast enums to integers for such tests.
Constants, Macros and enumerations only use upper-case letters. Words can, but don't have to be separated by an underscore. Use const for constants instead of define. If you use function macros, try to add the semicolon at the end so that it looks like a function call.
Member variables of classes, but not structs, should always be private or protected and get an underscore at the beginning. See also 9.9 Structs.
Type names (class members, functions and classes) start with a capital letter for each new word, with no underscores.
Global variables start with g_ and then continue with the standard naming conventions.
Template Parameters only use upper-case letters. Words don't have to be separated by an underscore. Use typename instead of class for template parameters. After the word template there is always a space.
For members, methods or variables that do the opposite thing use the correct name pairing, e.g.
Use the following order of declarations within a class: public before protected, protected before private, and methods before data members (variables). The keywords public, protected and private are aligned with the keyword class.
Class accessors should be named using the words 'Get' and 'Set'.
Class constructors should only set member variables to their initial values. Any complex initializations should go in an explicit Init() method. No memory must be allocated in the constructor, unless there is a specific reason for it. In general, we recommend brace-or-equal initializers for initialization (unless the initialization is performance-critical) which have the added benefit that you don't have to write repeat code for multiple constructors. If you use member-initializer lists, don't write each member on its own line. Instead leave them on one line, or split it into two lines with one tab indentation.
Class constructors should set initial values, unless otherwise required, due to performance reasons. Pointers must be initialized with nullptr. If there is a performance issue, the default initialization should be done as shown in the second example - do it exactly in the same order that the member variables were defined.
If class constructors support multiple data types, use the keyword explicit to avoid erroneous auto-conversion. Any constructor with a single argument should use explicit.
Use MAXON_DISALLOW_COPY_AND_ASSIGN in any class or struct by default, unless you need to copy your structure. The macro should go at the beginning of the declaration. Add a member CopyFrom instead, which provides safety (as it can return false). Classes that contain dynamic data by default should use MAXON_DISALLOW_COPY_AND_ASSIGN.
Use the keyword const whenever possible, especially for function input parameters and retrieval functions that don't modify a class.
Only overload (not override!) operators when there is an obvious benefit.
Generally classes should be preferred over structs. Use struct only for passive objects that carry data (and if necessary have an Init() function) and offer exclusively public members. If all members of a struct or class are public in the API, they do not need to, but can, carry the underscore. An example is the class Vector.
All input parameters passed by reference must be labelled const.
Class Members can, but don't have to be, aligned - usually alignment makes sense if the horizontal gaps are relatively small. If there are multiple pointers in one line, the members should be separated.