switch-case a new way

This design pattern solves the problem of having to implement huge switch - case statements and makes dynamic switch - case not dependent on the number of cases.

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Overview

This design pattern solves the problem of having to implement huge switch - case statements and makes dynamic switch - case not dependent on the number of cases.

Problem Description

If we have a program used for interpreting and executing commands, as like a Linux shell, and if we assume that we have 300 commands that needs to interpreted and executed, we would need to make a switch - case statement containing 300 cases, and what if we have more than 300 commands? Then, we would need more than 300 cases to handle all those commands. Here, we make a Design Pattern to solve this problem.

Design Pattern Steps

Step 1

Create for every case, only one separate function to handle all the logic of the case.

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void  HandleCase1 (int caseNumber) {    printf(" The Handled Case Number Is = %d",caseNumber);}void  HandleCase2 (int caseNumber) {    printf(" The Handled Case Number Is = %d",caseNumber);}void  HandleCase3 (int caseNumber) {    printf(" The Handled Case Number Is = %d",caseNumber);}

Put all of above function into a separate file and name it as HandleCases.cpp.

Step 2

Compile the above file as a shared object (dynamic library) using the following commands:

1. g++ -c -fpic HandleCases.cpp

   The above command generates an object file HandleCases.o.

2. g++ -shared -lc -o HandleCases.so HandleCases.o

   Now, we have a dynamic library containing all the case implementations.

Step 3

Create your main application where we will use this library instead of switch-cases.

1. Define a handle to our dynamic library.
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   void* FunctionLib;

2. Define a pointer to the called function.
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   void  (*Function)(int);

3. Open the dynamic library using the dlopen function.
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   FunctionLib = dlopen("dynamic library path", RTLD_LAZY);

4. Get the desired function pointer using the dlsym function.
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   Function =(void(*)(int))dlsym( FunctionLib, "HandleCase1");

5. Call this function using the above function pointer.
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   (*Function)(1);

6. Finally, close the dynamic library.
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   dlclose(FunctionLib);

Complete Code of Step 3

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#include <stdlib.h>#include <stdio.h>#include <dlfcn.h> // int main(int argc,char*argv[]){    // handle to Dynamic Libary    void* FunctionLib;     // Pointer to called function    void  (*Function)(int);     // Pointer to read the error    char *error;     // Open Dynamic Loadable Libary with absolute path     FunctionLib = dlopen("HandleCases.so",RTLD_LAZY);        if ((error = dlerror()) != NULL)    {        printf ("%s /n", error);        exit(1);    }    // point to our function need to call    Function =(void(*)(int))dlsym( FunctionLib, "HandleCase1");     if ((error = dlerror()) != NULL)     {        printf ("%s/n", error);        exit(1);    }    // call our function    (*Function)(1);    // close Dynamic libary    dlclose(FunctionLib);     return (0);}

License

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