[Segmentation Fault] fopen("filename","w")

Hello everybody,

I've a strange problem in a small application I'm working at.
This program reads a file, elaborates some data then writes new data onto another file. The destination file is a fixed-name file, named "results": not a variable name.
Yesterday I tested the program with a file - input files have a very simple structure - and everything went fine. Today I written a slightly bigger input file and...
...and it causes my program crash (Seg.fault) while "fopening" the results file.

Here's the code in the writing function.

Code:

---

void processaDati(){
               
               
                printf("Processing dati...\n\n");
                FILE * file;
                file=fopen ("risultati.psm","w");
                int i;
                printf("Let's begin...\n");
                //Setup
                fprintf(file, "def rAtomo = 1;\n");
//Other fprintf instructions omitted...

---

Maybe this piece of code is not very interesting, but I do not know what to post.

The curious problem is that the parsing & calculating phase of the program works well (I mean, it produces no errors!) so I believe the problem is not the input-file structure. Any hints?
Thanks a lot!

If you're using malloc, and you've trashed the memory pool by overrunning something, then anything can happen.

fopen usually calls malloc to allocate a FILE (which it returns to you as a pointer).
If malloc fails because you trashed memory, then fopen will fail.

Thank you,
I dont know what you mean by "trashing".
In the program I never malloc'd. I just declared arrays and a char*.

Well you're doing something wrong.

Just declaring something as char* ?

This is wrong for example, it trashes memory
char *p;
scanf("%s",p);

If you've got stuff like that, reading data into bare pointers, then the code is broken

You mean that if I made some mistakes elsewhere, these mistakes could cause the Seg-fault at fopening time?

However, I'm posting more code:


GLOBAL DECLARATIONS

Code:

---

typedef struct {
int indice;
float xpos;
float ypos;

} Atomo;

typedef struct{
int a;
int b;
int tipo;

} Legame;


Atomo atomi[100];
Legame legami[100];
int totAtomi,totLegami;

---

The following code open the input-file (arg.#1) and parse it line by line.
Then it checks the first char of the line, parse the line and fill a struct in the "atomi" and "legami" arrays. (notice: I removed some printf for clarity)

FILE READING FUNCTION

Code:

---

void carica(char * nomefile){
        FILE * file;
        file=fopen (nomefile,"r");
        totAtomi = 0;
        totLegami =0;

        char * linea;
       
        float x,y;

        int ia,ib,tipo,ind;
       
        printf("APRO: %s \n",nomefile);

        if (file==NULL) printf ("Error reading file \n");
        else
        {
                do {
                        fgets(linea,100,file);

                        if (linea[0] == 'A'){
                                sscanf(linea,"A %d | %f %f",&ind,&x,&y);

                                atomi[totAtomi].indice = ind;
                                atomi[totAtomi].xpos = x;
                                atomi[totAtomi].ypos = y;
                                totAtomi++;
                               
                        }
                        if (linea[0] == 'L'){
                                sscanf(linea,"L %d %d | %d",&ia,&ib,&tipo);
                               
                                legami[totLegami].tipo = tipo;
                                legami[totLegami].a = ia;
                                legami[totLegami].b = ib;
                                totLegami++;
                               
                        }
                } while ((feof(file) != 1));
               
               
        }
}

---

> fgets(linea,100,file);
Yeah, EXACTLY my point.

char *linea;
Where is this pointing - answer, the middle of nowhere.
You write up to 100 bytes over someone else's memory.

Try
char linea[100];
this has 100 bytes for your own personal use.

One more thing, replace your do while loop (which is wrong) with

Code:

---

while ( fgets(linea,100,file) != NULL ) {
  if (linea[0] == 'A' && totAtomi < 100 )
    // your sscanf stuff here
}

---

Thanks a lot for your advice! It seems to work now, declaring the 100-char array.

And yes, that was a ridiculous mistake... the totAtomi <100 :P

Thank you very much, you saved me hours of wasted time.