Defining/dealing with a dynamical structure (C)

[jarino]

Hi,

I have a simulation program that I want to port from matlab to C. But my C has gone rusty..

I have a system (in the mathematical sense) which, at each iteration, gets in a new state. In order to determine this new state, I have to determine first what is theoretically possible, and choose among these possibilities. When the simulation starts, I have but a few possible outcomes. As the simulation progresses, the number of possible outcomes increases. From a mere dozen to several hundred thousand possibilities.. So I try to deal with these outcomes in a dynamical way.

I am trying to get all this done in a function that will return the event that took place. I define

typedef struct{
    CITY FromCity;
    CITY ToCity;
    int TypeEvent;
    double ProbaEvent;
    double Time;
} EVENT;
 

in my .h, then declare

    EVENT *possible_events; 

in my function. Now I run (within the function) a main loop on states, and do the following (this is the first instance of possible_events being calloc/malloc/realloc-ed in any way):

possible_events=(EVENT *) realloc(possible_events,(nb_event+1)*sizeof(EVENT));
if (possible_events == NULL)
{
    printf("Problem reallocating possible_events\n");
    exit(1);
}
possible_events[nb_event]->FromCity=i;
 

And get the dreaded (306 is line 7 above):
stochastic_simulation.c: In function ‘Determine_Event’:
stochastic_simulation.c:306: error: invalid type argument of ‘->’

Can anyone remind me what it is that I should/should not be doing..? Thanks.

(I should add that, being in doubt, I tried the dot dereferencing instead of the ->, and was sent packing with a different love message from gcc, something about incompatible types I believe).

[weaknessforcats]

possible_events=(EVENT *) realloc(possible_events,(nb_event+1)*sizeof(EVENT) );
if (possible_events == NULL)
{
printf("Problem reallocating possible_events\n");
exit(1);
}
possible_events[nb_event]->FromCity=i;

In this code possible_events is an EVENT*. That makes the array and array of EVENT. An EVENT is not a pointer so you can't use the -> with an array element.

You would have to allocate an array of EVENT** so that you could have an array of EVENT* and then possible_events[nb_event] would be an EVENT* and the -> operator would be OK. If course, you would have to populate the array with valid EVENT addresses before using possible_events[nb_event].

[jarino]

Got it, thanks a lot for the help!

(I am fine using it as an array and with the . instead of the ->, I had typecasting problems when using the .)