Re: [Boost-users] [boost] Create Graph in Function

Subject: Re: [Boost-users] [boost] Create Graph in Function
From: James (j.thunes_at_[hidden])
Date: 2009-10-28 22:26:38

Jeremiah Willcock wrote:
> On Wed, 28 Oct 2009, Sandeep Gupta wrote:
>
>>
>>
>> On Wed, Oct 28, 2009 at 6:12 PM, James Thunes <j.thunes_at_[hidden]> 
>> wrote:
>>       Perhaps an easy answer, but I am working on adding a boost 
>> graph to an existing code. I would like to create the graph in
>>       a function (not main) and then read/modify it in a separate 
>> function. I am unsure as to what I need to pass between the
>>       functions to allow this to work.
>>
>>       In other words, I am able to correctly create the graph in a 
>> function and modify as necessary. This function will be
>>       called many times as the code runs and it is inefficient to 
>> recreate the graph every time. I want to create the graph once
>>       when the code is run and pass the created graph to the function.
>>
>>       Due to the structure of the code (mostly Fortran), I can not 
>> define the graph in the main function of the code.
>>
>>       My graph is defined as:
>>       adjacency_list<vecS, vecS, bidirectionalS, no_property, 
>> EdgeProperty> Graph;
>>
>>       Thank you for any help you can give,
>>       James
>>
>>       Try shared_ptr. Something like.
>>
>>
>>   function(){
>>    typedef  adjacency_list<vecS, vecS, bidirectionalS, no_property, 
>> EdgeProperty>  Graph;
>>    shared_ptr< Graph > gptr( new Graph(n) );
>>    return gptr;
>>    }
>
> You could also just declare the graph in whichever scope will end up 
> storing it and then pass it by reference to the construction function:
>
> void function(Graph& g) {
>   // build g, or build a temporary and assign it to g
> }
>
> Graph the_graph;
> function(the_graph);
>
> Where are you going to be putting the final graph?  Will it be in a 
> variable in your main(), even if it is not constructed there?
>
> -- Jeremiah Willcock
Jeremiah,

I'm sorry if I was not clear in my first post.  The majority of the code 
(along with the main routine) is written in Fortran. I am using the 
graph to update a number of arrays which are needed for this Fortran 
code.  I will create the graph in a subroutine (or c++ function) and 
modify it in another c++ function. The graph is not called in the main 
routine, only in subroutines.

I need to know the way the graph is stored so I can pass it back to the 
main function (or perhaps define it as a public variable).

In reference to the code snippet above, am I correct in reading it as 
the creating routine will be defined as:
  void function(Graph& g) {
  // build g, or build a temporary and assign it to g
}
and then the function to modify it would be defined as:
  void modify_the_graph(Graph& g){
    \\ some graph manipulations here
  }

-James Thunes