C++ Optimizations

[REinvestigator]

اقتباس من الموضوع الأصلي لـ GamingMasteR

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السلام عليكم
وجدت صفحة مكتوب بها هذا الموضوع عن تحسين طريقة كتابة كود السي :

[b]-----------------------------------------------
Use Initialization Lists
Always use initialization lists in constructors. For example, use
[/b]
كود PHP:

   TMyClass::TMyClass(const TData &data) : m_Data(data)
    {
    }  
 

rather than

كود PHP:

 TMyClass::TMyClass(const TData &data)
    {
         m_Data = data;
    }  
 

Without initialization lists, the variable's default constructor is invoked behind-the-scenes prior to the class's constructor, then its assignment operator is invoked. With initialization lists, only the copy constructor is invoked.
[b]-----------------------------------------------
Optimize For Loops
Wherever possible, count down to zero rather than up to n. For example, use
[/b]
كود PHP:

    for (i = n-1; i >= 0; --i)  
 

rather than

كود PHP:

    for (i = 0; i < n; ++i)  
 

The test is done every iteration and it's faster to test against zero than anything else. Note also that

كود PHP:

    ++i  
 

is faster than

كود PHP:

    i++  
 

when it appears in the third part of the for loop statement.
[b]-----------------------------------------------
Use 'int'
Always use the int data type instead of char or short wherever possible. int is always the native type for the machine.
-----------------------------------------------
Make Local Functions Static
Always declare local functions as static, e.g.,
[/b]
كود PHP:

    static void foo()  
 

This means they will not be visible to functions outside the .cpp file, and some C++ compilers can take advantage of this in their optimizations.
[b]-----------------------------------------------
Optimize If Statements
Factor out jumps. For example, use
[/b]
كود PHP:

    bar();
    if (condition)
    {
         undoBar();
         foo();
    }  
 

rather than

كود PHP:

    if (condition)
    {
         foo();
    }
    else
    {
         bar();
    }  
 

Use a profiler and good judgement to decide if undoing the bar() operation is faster than jumping.
[b]-----------------------------------------------
Optimize Switch Statements
Put the most common cases first.
-----------------------------------------------
Avoid Expensive Operations
Addition is cheaper than multiplication and multiplication is cheaper than division. Factor out expensive operations wherever possible.
-----------------------------------------------
Initialize on Declaration
Wherever possible, initialize variables at the time they're declared. For example,
[/b]
كود PHP:

    TMyClass x = data;  
 

is faster than

كود PHP:

    TMyClass x;
    x = data;  
 

Declaration then initialization invokes the object's default constructor then its assignment operator. Initializing in the declaration invokes only its copy constructor.
[b]-----------------------------------------------
Pass By Reference
Always try to pass classes by reference rather than by value. For example, use
[/b]
كود PHP:

    void foo(TMyClass &x)  
 

rather than

كود PHP:

    void foo(TMyClass x)  
 

[b]-----------------------------------------------
Delay Variable Declarations
Leave variable declarations right until the point when they're needed. Remember that when a variable is declared its constructor is called. This is wasteful if the variable is not used in the current scope.
-----------------------------------------------
Use 'op='
Wherever possible, use 'op=' in favour of 'op'. For example, use
[/b]
كود PHP:

    x += value;  
 

rather than

كود PHP:

    x = x + value;  
 

The first version is better than the second because it avoids creating a temporary object.
[b]-----------------------------------------------
Inline Small Functions
Small, performance critical functions should be inlined using the inline keyword, e.g.,
[/b]
كود PHP:

    inline void foo()  
 

This causes the compiler to duplicate the body of the function in the place it was called from. Inlining large functions can cause cache misses resulting in slower execution times.
[b]-----------------------------------------------
Use Nameless Objects
Wherever possible, use nameless objects. For example,
[/b]
كود PHP:

    foo(TMyClass("abc"));  
 

is faster than

كود PHP:

    TMyClass x("abc");
    foo(x);  
 

because, in the first case, the parameter and the object share memory