Static keywords are used in C to change the life cycle or access scope of a variable or function, depending on the context. ① The static variables in the function have a global life cycle, but are only visible within the function, and initialization is only performed once; ② The static members in the class belong to the entire class rather than the object, and all instances share the same data; ③ The static function can only access static members and can be called without creating an object; ④ The static in the global scope restricts the scope of the variable or function to the current file, encapsulation; ⑤ When using it, it is necessary to note that the static members in the class must be defined outside the class, thread safety of local static variables, and avoid abuse. Mastering static can improve code efficiency and structural clarity, but it also needs to be used with caution.
Static keyword in C is a keyword that is easy to use but not easy to understand thoroughly. It has different functions in different contexts, including static variables, static functions, static members, etc. Mastering its use can help you write more efficient and clearer code.
What are static variables?
Static variables are most commonly used inside functions and in classes.
Static variables in the function:
When you declare a static variable in a function, the life cycle of this variable will run throughout the program, but it will only be initialized once the first time it is executed to the declaration.
void count() {
static int counter = 0;
std::cout << counter << std::endl;
} Each time the count() function is called, counter value is incremented, rather than resetting to 0 each time. This is because the static variable is not destroyed as the function call ends.
Static member variables in the class:
The static member in the class belongs to the entire class, not an object of the class. That is, no matter how many objects are created, there is only one copy of the static member.
For example:
class MyClass {
public:
static int count;
MyClass() { count ; }
};
int MyClass::count = 0; // Must be defined outside the class In this way, count will be added when each object is constructed to count how many objects have been created.
What's special about the static function?
The static function in the class can only access static member variables and other static functions. Because it does not have this pointer, it cannot be bound to a specific object.
For example:
class Utility {
public:
static void printVersion() {
std::cout << "Version: " << version << std::endl;
}
private:
static std::string version;
};
std::string Utility::version = "1.0"; In this example, printVersion is a static function that can only access static member version . If you try to access non-static members, the compiler will report an error.
The advantage of static functions is that they can be called directly without creating objects, such as tool classes or helper functions that are very commonly used in this way.
What does static do in global scope?
Using the static keyword in a global scope (i.e. not in a class or function) affects the linkability of a variable or function.
- static global variable: Its scope is limited to the current file and other files cannot be accessed through extern.
- static function: It can also be used only in the files that define it to prevent naming conflicts.
for example:
// file1.cpp
static int secret = 42;
void showSecret() {
std::cout << secret << std::endl;
} Other source files cannot access secret , even if they know the name, it is useless. This is useful for package implementation details.
Several things to note when using static
- The static members in the class must be defined separately outside the class, otherwise an error occurs when linking.
- Static local variables can cause problems in multithreaded environments unless the initialization is thread-safe (C 11 The default thread-safe initialization of local static variables).
- Don't abuse static, especially in class designs, overuse can make the code difficult to maintain and test.
Basically that's it.
The key to understanding static is to remember that it changes the life cycle or access scope of a variable or function, and the specific behavior depends on the context used.
The above is the detailed content of C tutorial explaining the static keyword. For more information, please follow other related articles on the PHP Chinese website!
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