Question

I have few issues regarding when to use malloc or in this case strdup.
Below is the small function which I have stolen from internet.
I am trying to understand the code but stuck with few issues.
1. the code has assigned value to psrc and pdest. example

char* psrc = dups;  
char* pdest = s;  

Doubt: don’t we need to use malloc to allocate space for psrc and pdest.? If not then why.

1. pdest [0] = '\0';
   The above line allocates termination character at the starting of pdest string. then previously why we have assigned pdest to s . example char* pdest = s;?

Any help or criticism will be helpful to me.
Thanks and regards,
Sam

 char* deldupchars (char* s)    
 {      
   char* dups = strdup (s);      
   if (dups)     
   {      
    char* psrc = dups;      
    char* pdest = s;      
    char ch;      

    pdest [0] = '\0';      
    while ((ch = *psrc++) != '\0')    
    {            
     if (! strchr (pdest, ch))    
     {           
       *pdest++ = ch;           
     }             
    }       
    pdest [0] = '\0';      
    free (dups);       
   }      
   return s;       
 }       

Answer 1

char* psrc = dups;      

No need to allocate here since dups was allocated by strdup.

char* pdest = s;

No need to allocate here since s was allocated by the caller.

pdest[0] = '\0';

This writes into the contents of the string. The assignment pdest = s assigns pointers but not contents.