Structure of structures + linked list

Hi. I'm using a structure of structures, inside of which is a linked list, to pass information through a program. Unfortunately, occasionally it will have a segmentation fault.

Though more specific to Linux (I wrote the program on cygwin - which worked ok, moved onto Linux, compiled fine and then broke.. badly). I've been using Valgrind to try and narrow down the errors, and there's quite a few; of which I'm struggling to understand where the error is.

This is the structure declaration in a globals.h header file

Code:

---

typedef struct envSettings {
    struct {
        double answer;
        char problem[20];
    } problem;

    struct {
        unsigned int envID;           
        unsigned int currentPopLevel; 
        unsigned long runningTime;
        double fittestValue;
        double fittestScore;
        short mutateOn;
        unsigned long generationNo;
        unsigned long noOfChildren;
    }env;

    entity solution;
} envSettings;

typedef envSettings *environment;

---

The entity typedef would be:

Code:

---

typedef struct data{
    double fitnessScore;
    unsigned int charSolID;
    unsigned int parent1SolID;
    unsigned int parent2SolID;
    double value;
    char **character;
    short noOfChildren;
    struct data *next;
} data;

typedef data *entity;

---

In main (main.c) I'm doing the following:

Code:

---

environment instance = NULL;
    if( (instance = (environment)malloc(sizeof(envSettings))) == NULL ) {
        MALLOCERR;
    }
    instance->solution = NULL;   
   
    /* Initialise all variables */
    instance = (environment)initVars(instance);
    if( (instance = (environment)loadSettings(instance,"defaults.ini")) == NULL ) {
        free(instance);
        exit(1);
    }

---

With the call to initVars() doing the things such as:

Code:

---

environment initVars( environment instance ) {
  (void)strcpy(instance->problem.problem,"Sqrt");
    instance->problem.answer = 0;

    instance->env.envID = 0;
    instance->env.currentPopLevel = 0;
    instance->env.startTime = time(0);
    instance->env.endTime = 0;

  ...
  return instance;
}

---

The errors I'm seeing in valgrind all revolve around (though the size differs sometimes):

Quote:

---

Invalid write of size 4
...
Address 0xnnnnnnn is not stack'd, malloc'd or (recently free'd)

---

Would anyone kind enough please point out how I'm misusing structures of structures. TIA.

Are those objects (in red) part of the struct env?

Code:

---

typedef struct envSettings {
    struct {
        double answer;
        char problem[20];
    } problem;

    struct {
        unsigned int envID;           
        unsigned int currentPopLevel; 
        unsigned long runningTime;
        double fittestValue;
        double fittestScore;
        short mutateOn;
        unsigned long generationNo;
        unsigned long noOfChildren;
    }env;

    entity solution;
} envSettings;

typedef envSettings *environment;
.
.
.
typedef struct data{
    double fitnessScore;
    unsigned int charSolID;
    unsigned int parent1SolID;
    unsigned int parent2SolID;
    double value;
    char **character;
    short noOfChildren;
    struct data *next;
} data;

typedef data *entity;
.
.
.
environment initVars( environment instance ) {
  (void)strcpy(instance->problem.problem,"Sqrt");
    instance->problem.answer = 0;

    instance->env.envID = 0;
    instance->env.currentPopLevel = 0;
    instance->env.startTime = time(0); /* is startTime part of the env struct */
    instance->env.endTime = 0;        /* is endTime part of the env struct */

  ...
  return instance;
}

---

Code:

---

(instance = (environment)loadSettings(instance,"defaults.ini")) == NULL

---

I guess loadSettings() returns null when it fails, in which case you loose the reference to instance and the following call free(instance) is in fact a free(0) which, despite allowed, does nothing. Valgrind errors probably come from the fact you're using an invalid reference to instance, besides the case I pointed out, you probably loose the reference somewhere else in your code. I don't think this is a good idea to re-assign this variable each time you call a function modifying it.

Hi, thanks for the replies. Finally found some time to go through the program in more detail. As it turns out, although the convention I was using to allocate memory to the 2-dimensional arrays wasn't wrong, I found what I believe to be a more appropriate method to allocate the memory - so that all the data were in contiguous memory (found in the C-Faq (http://c-faq.com/aryptr/dynmuldimary.html - I won't be losing this link any time soon..).

The issue in the program was with when i was choosing to delete structures from the linked list. The logic being, if a new child entity were to be created, it would need space, and every so often a happy-go-lucky parent would be deleted just before a variable in its structure was accessed..

Anyway, thank you both for the replies, and apologies on the ambiguous initial post.