Segmentation fault

Question

Here is my code.

#include<stdio.h> int main(int argc,char** argv) { FILE* fp; fp=fopen(argv[1],"r"); struct element{ int value; char activity; }; typedef struct element element; element a; printf("%d",feof(fp)); }

Now if I don't give the last printf command it does not give me a segmentation fault, but if I give it printf it gives me a seg fault. Why?

I got the answer to my prev problem, now i have another problem

i had .txt appended to my input file in my makefile. Now i have another problem. on command make it gives error.

0make: *** [a.out] Error 1

why?

fopen() fails and so returns 0?

Martin James
– Martin James

2011-09-26 18:08:49 +00:00
Commented Sep 26, 2011 at 18:08 — Martin James
– Martin James, Commented Sep 26, 2011 at 18:08

Karoly Horvath · Accepted Answer · 2011-09-26 18:05:37Z

3

Check the return value of fopen (well, check the return value of any call), it probably failed to open the file.

answered Sep 26, 2011 at 18:05

Karoly Horvath

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1 Comment

Kraken Over a year ago

yeah, i had .txt appended in my makefile. Now i have another problem. on command make it gives error. 0make: *** [a.out] Error 1 why?

user405725 · Accepted Answer · 2011-09-26 18:08:46Z

Because you do not specify the file in a command line arguments, or because the file you have specified there could not be opened for some reason. In that case, fopen returns NULL, and when you pass that NULL to feof it crashes the program. You have to check return values and error codes, especially when functions may return NULL.

The correct code may look something like this:

#include <stdio.h> #include <stdlib.h> int main (int argc, char *argv[]) { FILE *fp; if (argc < 2) { fprintf (stderr, "Please specify the file name.\n"); return EXIT_FAILURE; } fp = fopen(argv[1], "r"); if (fp == NULL) { perror ("Cannot open input file"); return EXIT_FAILURE; } printf ("%d\n", feof (fp)); return EXIT_SUCCESS; }

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