We can merge these two functions in one using default value for the second argument and define 3 possible values for each funcion call: { 0: original, 1: left , 2: right}.

void top_view(node * root, int src=0)
{
    i f(root == NULL)
        return;

    if(src==0){        
        top_view(root->left, 1);        
        printf("%d ",root->data);
        top_view(root->right,2);        
    }    
    if(src==1){        
        top_view(root->left, 1);            
        printf("%d ",root->data);
    }
    if(src==2){
        printf("%d ",root->data);
        top_view(root->right,2);
    }    
}