Segmention Fault while in the middle of nested for loop - c

Question

I've written a code that needs to read in a series of values from a user specified data file (This could be up to 10,000 rows of data) which is done in the first for loop. In each row of values one of the variables is converted to a string which defines another set of input files(each containing ~20,000 rows of data) to load which are needed in the second for loop for calculations. This works well for the first few hundred iterations... it reads in everything correctly, and the resulting calculations (Calculations are omitted in the code below because the code produces the same problme with or without them) are as expected.
The problem is that when the first for loop reaches around 600 iterations it stops and produces the error: segmentation fault(core dumped)
I'm pretty sure this is a memory problem of some sort because if I've tested the code by omitting 4 of the input files in the second loop and it's capable of reaching a higher number of iterations....
This is the code:
#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main()
{
int num, i, j;
double X, Y;//
float Z;
char the_data[25], Z_name[10], input_1[50], input_2[50], input_3[50], input_4[50], input_5[50];
double a, b, c, d, e;
printf("Enter the name of the data file you are using:\n");
scanf("%24s", &the_data);
FILE *DATA = fopen(the_data,"r");
for (j=1; j<800; j++)
{
//***************Read data from a file, the variable Z is a floating point number which, when rounded to the nearest decimal place,
//********************determines which directory to load model data from for each value of X and Y
fscanf(DATA, "%lf %lf %f\n", &X, &Y, &Z);
//round Z to the nearest 1 decimal place
Z = Z * 10;
Z = roundf(Z);
Z = Z / 10;
//assign the full directory name to Z_name
sprintf(Z_name, "%.01fdirectory", Z);
//assign Z_name to input name string for path to the appropriate data file locations
sprintf(input_1, "./%s/a.txt", Z_name);
sprintf(input_2, "./%s/b.txt", Z_name);
sprintf(input_3, "./%s/c.txt", Z_name);
sprintf(input_4, "./%s/d.txt", Z_name);
sprintf(input_5, "./%s/e.txt", Z_name);
//Open the files
FILE *input1 = fopen(input_1, "r");
FILE *input2 = fopen(input_2, "r");
FILE *input3 = fopen(input_3, "r");
FILE *input4 = fopen(input_4, "r");
FILE *input5 = fopen(input_5, "r");
for (i=1; i < 10000; i++)
{
//For a given Z value, read in the corresponding values. Usually these input files have ~20000 values in each so the loop would be set to run until the end of the file
fscanf(input1, "%lf", &a);
fscanf(input2, "%lf", &b);
fscanf(input3, "%lf", &c);
fscanf(input4, "%lf", &d);
fscanf(input5, "%lf", &e);
}
//Test to see how far it gets in loop before giving up due to segmentation fault
printf("The iteration number is: %d\n", j);
}
printf("This will print if the program reaches the end of the first loop\n");
}
I'd appreciate any tips or pointers in dealing with this problem. Thanks!

Answer 1

You need to check the return value from fopen(). Since you're never closing the input files, you're probably hitting the limit on open files. Then fopen() returns NULL, and when you try to use that with fscanf() you get a segfault.
//Open the files
FILE *input1 = fopen(input_1, "r");
if (!input1) {
printf("open input_1 failed\n");
exit(1);
}
FILE *input2 = fopen(input_2, "r");
if (!input2) {
printf("open input_2 failed\n");
exit(1);
}
FILE *input3 = fopen(input_3, "r");
if (!input3) {
printf("open input_3 failed\n");
exit(1);
}
FILE *input4 = fopen(input_4, "r");
if (!input4) {
printf("open input_4 failed\n");
exit(1);
}
FILE *input5 = fopen(input_5, "r");
if (!input5) {
printf("open input_5 failed\n");
exit(1);
}
for (i=1; i < 10000; i++)
{
//For a given Z value, read in the corresponding values. Usually these input files have ~20000 values in each so the loop would be set to run until the end of the file
fscanf(input1, "%lf", &a);
fscanf(input2, "%lf", &b);
fscanf(input3, "%lf", &c);
fscanf(input4, "%lf", &d);
fscanf(input5, "%lf", &e);
}
//Test to see how far it gets in loop before giving up due to segmentation fault
printf("The iteration number is: %d\n", j);
fclose(input1);
fclose(input2);
fclose(input3);
fclose(input4);
fclose(input5);