(6.7)--6.7Lifecycleandscopeofglobalvari.pdf

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1、Life Cycle and Scope of Global VariablesLife Cycle and Scope of Global Variables6.7The storage types of variables can be divided into global variables,local variables,static global variables and static local variables according to the different positions and ways of variable definition.The storage t

2、ype of a variable determines the scope and life cycle of the variable.Life Cycle and Scope of Global Variables6.7means the scope of avariable,that is,wherethevariablecanbeused,and describes thespatial attribute of thevariable.Scopemeans a variables lifespan,that is,the time period in which the varia

3、ble exists during the entire program,and describes the time attribute of the variable.Life cycleLife Cycle and Scope of Global Variables6.7Global variables are variables defined outside of all functions.If global variables are not initialized when they are defined,they are automatically initialized

4、to 0.Global Variables The scope of a global variable is global,that is,it can be accessed anywhere in the program.The lifetime of a global variable is the whole program,which is generated when the program starts and disappears when the program ends.Life Cycle and Scope of Global Variables6.7In a pro

5、gram with multi-file structure,the global variable defined in a source file must be added with an external declaration before being used in other source files.The syntax isextern ;Life Cycle and Scope of Global Variables6.7/globalVar.cpp#includeusing namespace std;int g_fac;void Fac(int);int main()i

6、nt n=5;Fac(n);cout“The factorial of nis g_facendl;return 0;Life Cycle and Scope of Global Variables6.7Tip：void Fac(int n)int i;g_fac=1;for(i=2;i=n;i+)g_fac*=i;Global variables will reduce the independence between functions,and minimize the use of global variables when writing programs.Life Cycle and

7、 Scope of Global Variables6.7A global variable,which is added a keyword static on the left of its definition,is called a static global variable.If the static global variable is not initialized when it is defined,it is automatically initialized to 0.The definition syntax of static global variables isStatic Global Variablesstatic ;Static global variables,which have the same life cycle as global variables,only have the file scope,that is,in a multi-file structure program,static local variables defined in a source file can only be used in the source file.