EMF In C++ Code Coventions

The project aims to be the most as it can close to the Java corresponding project. So the code convention of the project is based on the standard Java code convention.


Why Have Code Conventions

Code conventions are important to programmers for a number of reasons:

  • 80% of the lifetime cost of a piece of software goes to maintenance.
  • Hardly any software is maintained for its whole life by the original author.
  • Code conventions improve the readability of the software, allowing engineers to understand new code more quickly and thoroughly.
  • If you ship your source code as a product, you need to make sure it is as well packaged and clean as any other product you create.


This document reflects the Java language coding standards presented in the Java Language Specification, from Sun Microsystems. Major contributions are from Peter King, Patrick Naughton, Mike DeMoney, Jonni Kanerva, Kathy Walrath, and Scott Hommel.

For questions concerning adaptation, modification, or redistribution of this document, please read our copyright notice at http://java.sun.com/docs/codeconv/html/Copyright.doc.html .

Comments on this document should be submitted to our feedback form at http://java.sun.com/docs/forms/sendusmail.html .

File Names

This section lists commonly used file suffixes and names.

File Suffixes

We uses the following file suffixes:

File Type Suffix
C++ header .h
C++ impl .cpp
Java source .java

Common File Names

Frequently used file names include:

File Name Use
makefile The preferred name for makefiles.
We use make to build our software.
README The preferred name for the file that summarizes the
contents of a particular directory.

File Organization

A file consists of sections that should be separated by blank lines and an optional comment identifying each section.

Files longer than 2000 lines are cumbersome and should be avoided.

For an example of a Java program properly formatted, see "Source File Example".

C++ Source Files

Each Java source file contains a single public class or interface. When private classes and interfaces are associated with a public class, you can put them in the same source file as the public class. The public class should be the first class or interface in the file. Java source files have the following ordering:

  • Beginning comments (see “Beginning Comments” on page 4)
  • Package and Import statements; for example:
    import java.applet.Applet;
    import java.awt.*;
    import java.net.*;
  • Class and interface declarations (see “Class and Interface Declarations”)
Beginning Comments

All source files should begin with a c-style comment that lists the programmer(s), the date, a copyright notice, and also a brief description of the purpose of the program. For example:

 * Classname
 * Version info
 * Copyright notice
Package and Import Statements

The first non-comment line of most Java source files is a package statement. After that, import statements can follow. For example:

package java.awt;
import java.awt.peer.CanvasPeer;
Class and Interface Declarations

The following table describes the parts of a class or interface declaration, in the order that they should appear. See Source File Example for an example that includes comments.

Part of Class/Interface
1 Class/interface documentation
comment (/**...*/)
See “Documentation Comments” on page 9 for
information on what should be in this comment.
2 class or interface statement
3 Class/interface implementation
comment (/*...*/), if necessary
This comment should contain any class-wide or
interface-wide information that wasn’t
appropriate for the class/interface
documentation comment.
4 Class (static) variables First the public class variables, then the
protected , and then the private.
5 Instance variables First public, then protected, and then
private .
6 Constructors
7 Methods These methods should be grouped by functionality
rather than by scope or accessibility. For
example, a private class method can be in
between two public instance methods. The goal is
to make reading and understanding the code easier.


Four spaces should be used as the unit of indentation. The exact construction of the indentation (spaces vs. tabs) is unspecified. Tabs must be set exactly every 8 spaces (not 4).

Line Length

Avoid lines longer than 80 characters, since they’re not handled well by many terminals and tools.

Note : Examples for use in documentation should have a shorter line length—generally no more than 70 characters.

Wrapping Lines

When an expression will not fit on a single line, break it according to these general principles:

  • Break after a comma.
  • Break before an operator.
  • Prefer higher-level breaks to lower-level breaks.
  • Align the new line with the beginning of the expression at the same level on the previous line.
  • If the above rules lead to confusing code or to code that’s squished up against the right margin, just indent 8 spaces instead.

    Here are some examples of breaking method calls:

       function(longExpression1, longExpression2, longExpression3,
                longExpression4, longExpression5);
       var = function1(longExpression1,

    Following are two examples of breaking an arithmetic expression. The first is preferred, since the break occurs outside the parenthesized expression, which is at a higher level.

    longName1 = longName2 * (longName3 + longName4 - longName5)
                + 4 * longname6; // PREFER
    longName1 = longName2 * (longName3 + longName4
                             - longName5) + 4 * longname6; // AVOID

    Following are two examples of indenting method declarations. The first is the conventional case. The second would shift the second and third lines to the far right if it used conventional indentation, so instead it indents only 8 spaces.

    someMethod(int anArg, Object anotherArg, String yetAnotherArg,
               Object andStillAnother) {
    private static synchronized horkingLongMethodName(int anArg,
            Object anotherArg, String yetAnotherArg,
            Object andStillAnother) {

    Line wrapping for if statements should generally use the 8-space rule, since conventional (4 space) indentation makes seeing the body difficult. For example:

    if ((condition1 && condition2)
        || (condition3 && condition4)
        ||!(condition5 && condition6)) { //BAD WRAPS
        doSomethingAboutIt(); //MAKE THIS LINE EASY TO MISS
    if ((condition1 && condition2)
            || (condition3 && condition4)
            ||!(condition5 && condition6)) {
    if ((condition1 && condition2) || (condition3 && condition4)
            ||!(condition5 && condition6)) {

    Here are three acceptable ways to format ternary expressions:

    alpha = (aLongBooleanExpression) ? beta : gamma;
    alpha = (aLongBooleanExpression) ? beta
                                     : gamma;
    alpha = (aLongBooleanExpression)
            ? beta
            : gamma;


Java programs can have two kinds of comments: implementation comments and documentation comments. Implementation comments are those found in C++, which are delimited by /*...*/, and //. Documentation comments (known as “doc comments”) are Java-only, and are delimited by /**...*/. Doc comments can be extracted to HTML files using the javadoc tool.

Implementation comments are mean for commenting out code or for comments about the particular implementation. Doc comments are meant to describe the specification of the code, from an implementation-free perspective. to be read by developers who might not necessarily have the source code at hand.

Comments should be used to give overviews of code and provide additional information that is not readily available in the code itself. Comments should contain only information that is relevant to reading and understanding the program. For example, information about how the corresponding package is built or in what directory it resides should not be included as a comment.

Discussion of nontrivial or nonobvious design decisions is appropriate, but avoid duplicating information that is present in (and clear from) the code. It is too easy for redundant comments to get out of date. In general, avoid any comments that are likely to get out of date as the code evolves.

Note : The frequency of comments sometimes reflects poor quality of code. When you feel compelled to add a comment, consider rewriting the code to make it clearer.

Comments should not be enclosed in large boxes drawn with asterisks or other characters.
Comments should never include special characters such as form-feed and backspace.

Implementation Comment Formats

Programs can have four styles of implementation comments: block, single-line, trailing and end-of-line.

Block Comments

Block comments are used to provide descriptions of files, methods, data structures and algorithms. Block comments should be used at the beginning of each file and before each method. They can also be used in other places, such as within methods. Block comments inside a function or method should be indented to the same level as the code they describe.

A block comment should be preceded by a blank line to set it apart from the rest of the code. Block comments have an asterisk “*” at the beginning of each line except the first.

 * Here is a block comment.

Block comments can start with /*-, which is recognized by indent(1) as the beginning of a block comment that should not reformatted. Example:

 * Here is a block comment with some very special
 * formatting that I want indent(1) to ignore.
 *     one
 *         two
 *             three

Note : If you don’t use indent(1), you don’t have to use /*- in your code or make any other concessions to the possibility that someone else might run indent(1) on your code.

See also “Documentation Comments” on page 9.

Single-Line Comments

Short comments can appear on a single line indented to the level of the code that follows. If a comment can’t be written in a single line, it should follow the block comment format (see section 5.1.1). A single-line comment should be preceded by a blank line. Here’s an example of a single-line comment in Java code (also see “Documentation Comments” on page 9):

if (condition) {
    /* Handle the condition. */
Trailing Comments

Very short comments can appear on the same line as the code they describe, but should be shifted far enough to separate them from the statements. If more than one short comment appears in a chunk of code, they should all be indented to the same tab setting. Avoid the assembly language style of commenting every line of executable code with a trailing comment.

Here’s an example of a trailing comment in Java code (also see “Documentation Comments” on page 9):

if (a == 2) {
    return TRUE; /* special case */
} else {
    return isprime(a); /* works only for odd a */
End-Of-Line Comments

The // comment delimiter begins a comment that continues to the newline. It can comment out a complete line or only a partial line. It shouldn’t be used on consecutive multiple lines for text comments; however, it can be used in consecutive multiple lines for commenting out sections of code. Examples of all three styles follow:

if (foo > 1) {
// Do a double-flip.
return false; // Explain why here.
//if (bar > 1) {
// // Do a triple-flip.
// ...
// return false;

Documentation Comments

Note : See “Java Source File Example” on page 19 for examples of the comment formats described here.

For further details, see “How to Write Doc Comments for Javadoc” which includes information on the doc comment tags (@return, @param, @see):


For further details about doc comments and javadoc, see the javadoc home page at:


Doc comments describe Java classes, interfaces, constructors, methods, and fields. Each doc comment is set inside the comment delimiters /**...*/, with one comment per API. This comment should appear just before the declaration:

 * The Example class provides ...
class Example { ...

Notice that classes and interfaces are not indented, while their members are. The first line of doc comment (/**) for classes and interfaces is not indented; subsequent doc comment lines each have 1 space of indentation (to vertically align the asterisks). Members, including constructors, have 4 spaces for the first doc comment line and 5 spaces thereafter.

If you need to give information about a class, interface, variable, or method that isn’t appropriate for documentation, use an implementation block comment (see section 5.1.1) or single-line (see section 5.1.2) comment immediately after the declaration. For example, details about the implementation of a class should go in in such an implementation block comment following the class statement, not in the class doc comment.

Doc comments should not be positioned inside a method or constructor definition block, because Java associates documentation comments with the first declaration after the comment.


Number Per Line

One declaration per line is recommended since it encourages commenting. In other words,

int level; // indentation level
int size; // size of table

is preferred over

int level, size;

In absolutely no case should variables and functions be declared on the same line. Example:

long dbaddr, getDbaddr(); // WRONG!

Do not put different types on the same line. Example:

int foo, fooarray[]; //WRONG!

Note : The examples above use one space between the type and the identifier. Another acceptable alternative is to use tabs, e.g.:

int level; // indentation level
int size; // size of table
Object currentEntry; // currently selected table entry


Put declarations only at the beginning of blocks. (A block is any code surrounded by curly braces “” and “ ”.) Don’t wait to declare variables until their first use; it can confuse the unwary programmer and hamper code portability within the scope.

void MyMethod() {
    int int1; // beginning of method block
    if (condition) {
        int int2; // beginning of "if" block

The one exception to the rule is indexes of for loops, which in Java can be declared in the for statement:

for (int i = 0; i < maxLoops; i++) { ...

Avoid local declarations that hide declarations at higher levels. For example, do not declare the same variable name in an inner block:

int count;
func() {
    if (condition) {
        int count; // AVOID!


Try to initialize local variables where they’re declared. The only reason not to initialize a variable where it’s declared is if the initial value depends on some computation occurring first.

Class and Interface Declarations

When coding Java classes and interfaces, the following formatting rules should be followed:

  • No space between a method name and the parenthesis “\(“ starting its parameter list
  • Open brace “{” appears at the end of the same line as the declaration statement
  • Closing brace “}” starts a line by itself indented to match its corresponding opening statement, except when it is a null statement the “}” should appear immediately after the “{“
    class Sample extends Object {
        int ivar1;
        int ivar2;
        Sample(int i, int j) {
            ivar1 = i;
            ivar2 = j;
        int emptyMethod() {}
  • Methods are separated by a blank line


Simple Statements

Each line should contain at most one statement. Example:

argv++; argc--; // AVOID!

Do not use the comma operator to group multiple statements unless it is for an obvious reason. Example:

if (err) {
    Format.print(System.out, “error”), exit(1); //VERY WRONG!

Compound Statements

Compound statements are statements that contain lists of statements enclosed in braces “ statements ”. See the following sections for examples.

  • The enclosed statements should be indented one more level than the compound statement.
  • The opening brace should be at the end of the line that begins the compound statement; the closing brace should begin a line and be indented to the beginning of the compound statement.
  • Braces are used around all statements, even singletons, when they are part of a control structure, such as a if-else or for statement. This makes it easier to add statements without accidentally introducing bugs due to forgetting to add braces.

return Statements

A return statement with a value should not use parentheses unless they make the return value more obvious in some way. Example:


return myDisk.size();

return (size ? size : defaultSize);

if, if-else, if-else-if-else Statements

The if-else class of statements should have the following form:

if (condition) {

if (condition) {
} else {

if (condition) {
} else if (condition) {
} else if (condition) {

Note : if statements always use braces . Avoid the following error-prone form:

if (condition) //AVOID! THIS OMITS THE BRACES {}!

for Statements

A for statement should have the following form:

for (initialization; condition; update) {

An empty for statement (one in which all the work is done in the initialization, condition, and update clauses) should have the following form:

for (initialization; condition; update);

When using the comma operator in the initialization or update clause of a for statement, avoid the complexity of using more than three variables. If needed, use separate statements before the for loop (for the initialization clause) or at the end of the loop (for the update clause).

while Statements

A while statement should have the following form:

while (condition) {

An empty while statement should have the following form:

while (condition);

do-while Statements

A do-while statement should have the following form:

do {
} while (condition);

switch Statements

A switch statement should have the following form:

switch (condition) {
    case ABC:
        /* falls through */
    case DEF:
    case XYZ:

Every time a case falls through (doesn’t include a break statement), add a comment where the break statement would normally be. This is shown in the preceding code example with the /* falls through */ comment.

Every switch statement should include a default case. The break in the default case is redundant, but it prevents a fall-through error if later another case is added.

try-catch Statements

A try-catch statement should have the following format:

try {
} catch (ExceptionClass e) {

White Space

Blank Lines

Blank lines improve readability by setting off sections of code that are logically related. Two blank lines should always be used in the following circumstances:

  • Between sections of a source file
  • Between class and interface definitions

    One blank line should always be used in the following circumstances:

  • Between methods
  • Between the local variables in a method and its first statement
  • Before a block (see section 5.1.1) or single-line (see section 5.1.2) comment
  • Between logical sections inside a method to improve readability

Blank Spaces

Blank spaces should be used in the following circumstances:

  • A keyword followed by a parenthesis should be separated by a space. Example:
    while (true) {

    Note that a blank space should not be used between a method name and its opening parenthesis. This helps to distinguish keywords from method calls.

  • A blank space should appear after commas in argument lists.
  • All binary operators except . should be separated from their operands by spaces. Blank spaces should never separate unary operators such as unary minus, increment (“++”), and decrement (“--”) from their operands. Example:
    a += c + d;
    a = (a + b) / (c * d);
    while (d++ = s++) {
    prints("size is " + foo + "\n");
  • The expressions in a for statement should be separated by blank spaces. Example:
    for (expr1; expr2; expr3)
  • Casts should be followed by a blank. Examples:
    myMethod((byte) aNum, (Object) x);
    myFunc((int) (cp + 5), ((int) (i + 3))
                                 + 1);

Naming Conventions

Naming conventions make programs more understandable by making them easier to read. They can also give information about the function of the identifier—for example, whether it’s a constant, package, or class—which can be helpful in understanding the code.

The conventions given in this section are high level. Further conventions are given at (to be determined).

Identifier Type Rules for Naming Examples
Classes Class names should be nouns, in mixed case
with the first letter of each internal word capitalized.
Try to keep your class names simple
and descriptive. Use whole words—avoid
acronyms and abbreviations (unless the abbreviation
is much more widely used than the
long form, such as URL or HTML).
class Raster;
class ImageSprite;
Interfaces Interface names should be capitalized like
class names.
interface RasterDelegate;
Methods Methods should be verbs, in mixed case with
the first letter lowercase, with the first letter of
each internal word capitalized.
Variables Except for variables, all instance, class, and
class constants are in mixed case with a lowercase
first letter. Internal words start with capital letters.
Variable names should be short yet meaningful.
The choice of a variable name should be
mnemonic— that is, designed to indicate to the
casual observer the intent of its use. One-character
variable names should be avoided except
for temporary “throwaway” variables. Common
names for temporary variables are i, j, k,
m, and n for integers; c, d, and e for characters.
int i;
char *cp;
float myWidth;
Constants The names of variables declared class constants
and of ANSI constants should be all
uppercase with words separated by underscores
(“_”). (ANSI constants should be
avoided, for ease of debugging.)
int MIN_WIDTH = 4;
int MAX_WIDTH = 999;
int GET_THE_CPU = 1;

Code Examples

Java Source File Example

The following example shows how to format a Java source file containing a single public class. Interfaces are formatted similarly. For more information, see “Class and Interface Declarations” on page 4 and “Documentation Comments” on page 9

 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *   http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
package java.blah;
import java.blah.blahdy.BlahBlah;
 * Class description goes here.
 * @version 1.10 04 Oct 1996
 * @author Firstname Lastname
public class Blah extends SomeClass {
    /* A class implementation comment can go here. */
    /** classVar1 documentation comment */
    public static int classVar1;
     * classVar2 documentation comment that happens to be
     * more than one line long
    private static Object classVar2;
    /** instanceVar1 documentation comment */
    public Object instanceVar1;
    /** instanceVar2 documentation comment */
    protected int instanceVar2;
    /** instanceVar3 documentation comment */
    private Object[] instanceVar3;
     * ...method Blah documentation comment...
    public Blah() {
        // ...implementation goes here...
     * ...method doSomething documentation comment...
    public void doSomething() {
        // ...implementation goes here...
     * ...method doSomethingElse documentation comment...
     * @param someParam description
    public void doSomethingElse(Object someParam) {
        // ...implementation goes here...