seg faulting on array declaration

[rpeters1]

i havent programmed in C in years, i need to however for a project.

anyway, i'm reading in a data file and parsing it using basic file pointers. i read in all the data fine. however, when i try to declare a simple array, say, int my_array[10];, it seg faults. if i remove the code that reads in the data and declare the same array, it works fine.

any ideas? i can post the code if needed. thanks!

 

[countdrak]

If the seg fault is showing on the array declaration, it could be very misleading. Your error could be somewhere before the declaration. Here are a few things I would try:

1. comment out the int my_array[10]; line and see if you still get seg fault. If you do, do #2, if not then post the code.

2. put a printf statement before array declaration. If the seg fault happens before the printf is executed, go up a few lines and try again. Until you find the exact line where the seg fault is happening.

If 1 & 2 fail, post the code.

 

[rpeters1]

here is the code. it actually now seems that i can have an array of size 1 and it wont seg fault. a value of 4 will seg fault at the end of the program (after data is printed). a value of 5 will not seg fault. a value of 20 will seg fault before the data is printed.

should i use malloc?



#include <stdio.h>



int main(int argc, char *argv[])
{
int my_array[1];
FILE *ifp;
char *data;
int num_places = 0, num_transitions = 0, init_marking;

ifp = fopen ("input.dat", "r");

if (ifp == NULL)
{
fprintf(stderr, "Can't open input file!\n");
return 0;
}
else
{

fscanf(ifp, " PN PLACES: ");
while (fscanf(ifp, "%s", data) != EOF && (strcmp(data, "PN") != 0))
{
printf("%s", data);
num_places++;
}

printf("\n");

fscanf(ifp, " TRANSITIONS:");
while (fscanf(ifp, "%s", data) != EOF && (strcmp(data, "PN") != 0))
{
printf("%s", data);
num_transitions++;
}

printf("\n");

int i;
for (i = 1; i <= num_transitions; i++)
{
fscanf(ifp, " PLACES FOR INPUT %s:", data);
while (fscanf(ifp, "%s", data) != EOF && (strcmp(data, "PN") != 0))
printf("%s", data);

printf("\n");
}

for (i = 1; i <= num_transitions; i++)
{
fscanf(ifp, " PLACES FOR OUTPUT %s:", data);
while (fscanf(ifp, "%s", data) != EOF && (strcmp(data, "PN") != 0))
printf("%s", data);

printf("\n");
}

fscanf(ifp, " INITIAL MARKING: %s", data);
printf("%s", data);

printf("\n");

fscanf(ifp, " PN MAX TRANSITIONS FIRING: %s", data);
printf("%s", data);
}

return 0;
}

 

[DaveSinkula]

Dangling pointer.

 char *data;

Point to writeable memory to avoid seg faulting. Or use an array.