I couldn't figure out what error is there in my code - segmentation fault core dumped error in C

Question

#include<stdio.h>

void main()
{
    FILE *a[10];  
    int i,j,k;
    float b[10][4][4];
    for(i=0;i<8;i++)
    {
        char filename[100];
        sprintf(filename,"infile%d.txt",i);
        a[i]=fopen(filename,"r");
    }

    for(i=0;i<8;i++)
    {
        for(j=0;j<2;j++)
        {
            for (k=0;k<3;k++)
            { 
                fscanf(a[i],"%f",&b[i][j][k]);
            }
        }
    }

    for (i=0;i<8;i++)
    {
        printf("\n-----------------%d--------------------",i);
        for(j=0;j<2;j++)
        {
            for(k=0;k<3;k++)
            {
                printf("\nb[%d][%d][%d]=%f",i,j,k,b[i][j][k]);
            }
        }
    }
}

I have written the above code in C. Which just reads 8 different files and print it in terminal. The file name is infile0, infile1 and son on up to infile7. Though the code runs, it shows segmentation fault core dumped in the terminal. I couldn't figure out why this happens at all. Can some one help me figure out the mistake in the code.

What if the files are not there? Does it print any of the output? — Eugene Sh., Mar 14 '19 at 18:47
Read [*How to debug small programs*](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/) — Basile Starynkevitch, Mar 14 '19 at 19:15

fennecdjay · Answer 1 · 2019-03-14T19:28:44.710

3

Compiling with -g and running trough valgrind gives an error line 19 when no files are present.
Maybe you should add

if(!a[i])continue;

before scanf. (and set some message or default values).

also have a look at Input validation using scanf(), as you should check scanf return value.

I hope it helps, this my my first so contribution.

EDIT: the -g flag is for your compiler, e.g

gcc -g myfile.c -o myfile

then run your binary trough valgrind.
It will tell you any problems with memory: leaks, invalid red/write...

valgrind ./myfile

Don't forget to install valgrind if it is not on your system.

edited Mar 14 '19 at 19:28

answered Mar 14 '19 at 19:04

fennecdjay

56
1
6

Can you please elaborate your first answer about the -g ...valgrind thing..How should put that command while compiling and running in terminal – user135580 Mar 14 '19 at 19:06
Sure. I'll edit my answer. – fennecdjay Mar 14 '19 at 19:13
gcc filename.c -o filename....I used this command...how should I modify this to get what you said . – user135580 Mar 14 '19 at 19:15

score 1 · Answer 2 · answered Mar 14 '19 at 19:16

A lot of remarks can be done from your code

1) In

 void main()

main returns an int, not void, so must be

int main()

2) In

 FILE *a[10];  
 ..
 for(i=0;i<8;i++)
 {
    ...
    a[i]=fopen(filename,"r");

why do you have an array with 10 entries to only use 8 of them ?, better to have

  FILE *a[8];

3) 10 (becoming 8) is used a lot of times in your code, if you decide to change the number of elements you will have to change it every where, it is more simple to use a #define or sizeof(a)/sizeof(a[0])

4) In

char filename[100];
sprintf(filename,"infile%d.txt",i);

you are very generous with the needed size, even your int are in 64b and you increase so much the number of entries in a (no change to have enough stack nor file description anyway) 20 digits are enough for a positive number, so char filename[20+10+1]; is enough

5) In

float b[10][4][4];
...
for(j=0;j<2;j++)
{
   for (k=0;k<3;k++)

like for 2) there is no reason to use a so large array if you do not use all the entries

6) In

 fscanf(a[i],"%f",&b[i][j][k]);

you do not check if the corresponding file was open so if a[i] is not NULL, probably your segmentation fault comes because a file wasn't open
you do not detect the end of file nor if the file doesn't contain a valid float, you need to do for instance if (fscanf(a[i],"%f",&b[i][j][k]) != 1) { ...error management... }

Thanks for your answers. Unfortunately, nothing works.The error continue to exist — user135580, Mar 14 '19 at 19:30
@user135580 what are you doing when a file is not open ? what the files contain ? — bruno, Mar 14 '19 at 19:55

I couldn't figure out what error is there in my code - segmentation fault core dumped error in C

2 Answers2