On Wed, 28 Oct 2009, Sandeep Gupta wrote:

On Wed, Oct 28, 2009 at 6:12 PM, James Thunes 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 Graph;

Thank you for any help you can give, James

Try shared_ptr. Something like.

  function(){    typedef  adjacency_list  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

On Wed, 28 Oct 2009, James wrote:

Jeremiah Willcock wrote:

...

On Wed, 28 Oct 2009, Sandeep Gupta wrote:

...

On Wed, Oct 28, 2009 at 6:12 PM, James Thunes 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 Graph;

Thank you for any help you can give, James

Try shared_ptr. Something like.

function(){ typedef adjacency_list 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 }

Where is the variable holding the graph going to be? If it doesn't have a Fortran type the variable cannot be in Fortran code. Are you going to have a global variable (in C++) that contains the graph? Otherwise, you might need to use a raw (not shared) pointer to the graph, managing the memory yourself, and pass it between Fortran and C++ as either some kind of interoperability C pointer type (in newer Fortran versions), a large enough integer, or maybe a Cray pointer. -- Jeremiah Willcock

On Wed, 28 Oct 2009, James wrote:

Jeremiah Willcock wrote:

...

On Wed, 28 Oct 2009, James wrote:

...

Jeremiah Willcock wrote:

...

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 }

Where is the variable holding the graph going to be? If it doesn't have a Fortran type the variable cannot be in Fortran code. Are you going to have a global variable (in C++) that contains the graph? Otherwise, you might need to use a raw (not shared) pointer to the graph, managing the memory yourself, and pass it between Fortran and C++ as either some kind of interoperability C pointer type (in newer Fortran versions), a large enough integer, or maybe a Cray pointer.

-- Jeremiah Willcock

That is the issue. I agree that to manipulate the graph in the Fortran portion of the code would be difficult (due the lack of a comparable data type). Luckily, I don't need to modify the graph in the Fortran portion of the code, I just need to allow for a c++ function to access the graph. If I can define the graph as a global variable in c++ and negate the need to pass the graph from the create_graph function to the modify_graph function via the Fortran main routine: Create_Graph.cpp -> Main.f -> Modify_Graph.cpp would be great.

Would I accomplish this as: in create_graph.cpp Graph& g;

void create_graph(){ \\ create graph }

and in modify_graph.cpp extern Graph& g;

void modify_graph(){ \\... }

The storage for the graph needs to be somewhere; making the variables of type Graph rather than Graph& would solve that problem. -- Jeremiah Willcock