string replacement in C

Please Using free to free the memory after use it

/*
*Function:str_replace
*Parameter:char* search,char* replace,char* str
*Call:char *str_replace(char* search,char* replace,char* str);
*Return: string 
*Required:malloc.h
*Required:string.h
*Description: replace the string in the string
*/
char *str_replace(char* search,char* replace,char* str)
{
    int lstr,lse,lre;
    char* r,*p,*nptr;
    lse=strlen(search);
    lre=strlen(replace);
    lstr=strlen(str);
    if(lse>lstr)
    { 
        return NULL;
    }
    r=(char* )malloc(lstr+1);
    if(r==NULL)
    {
        printf("Failed to allocate memory");
        exit(-2);
    }
    strcpy(r,str);                    /*Copy the string to new memory*/
    p=strstr(r,search);
    while(p!=NULL)
    {
        if(lse==lre)
        {
            memcpy(p,replace,lre);  /*Just Copy the string*/
        }else if(lse>lre)            /*No allocation required*/
        {
            memset(p,' ',lse);        /*Clear it first*/
            memcpy(p,replace,lre);    /*Copy data*/
            memcpy(p+lre,p+lse,lstr-(p-r+lse)+1);/*Remove the blanks*/
        }else{
            nptr=realloc(r,lstr+(lre-lse));/*Expand the space first*/
            if(nptr==NULL)
            {
                printf("Failed to allocate memory");
                exit(-2);
            }
            r=nptr;
            memcpy(p+lre,p+lse,lstr-(p-r+lse)+1);/*Move data now*/
            memcpy(p,replace,lre);
        }
        p=strstr(p+lre,search);        /*To prevent the replace string contained the search string*/
    }
    return r;
}