How to write program to run Only one executable in Unix

<code><var style="font-style: normal; color: rgb(0, 0, 176);">The following program to make sure that we are running only one instance of a program in Unix :-) 

The concept is based on the named key Creation when creating any IPC mechanism. 


int</var> main()
{   
    sem_t *mysem;
    mysem = sem_open(<kbd style="font-style: normal; color: rgb(96, 0, 48);">"MyUniqueName"</kbd>, O_CREAT|O_EXCL);
    <var style="font-style: normal; color: rgb(0, 0, 176);">if</var> ( mysem == NULL )
    {      
        fprintf(stderr, <kbd style="font-style: normal; color: rgb(96, 0, 48);">"I am already running!\n"</kbd>);
        exit(1);
    }  
 
    <cite style="font-style: normal; color: rgb(0, 112, 0);">/* the app code here*/</cite>    

    <cite style="font-style: normal; color: rgb(0, 112, 0);">/* end of the app */</cite>   

    sem_unlink(<kbd style="font-style: normal; color: rgb(96, 0, 48);">"MyUniqueName"</kbd>); 
    sem_close(mysem);
}</code>