Segmentation fault inside printf statement

Question

I get a Segmentation fault inside the insert function within the printf statment

#include <stdio.h>
#include <stdlib.h>
void Insert(char w[])
{
int j;
int n=5;
printf("word is %s AFTER\n", w);
}


int main(int argc, char *argv[])
{
        FILE *fp;
        if (argc !=2)
                fp=fopen("words.txt", "r");
        else
                fp=fopen(argv[1], "r");
        char line[28];
        while(!feof(fp)){
                fgets(line, 256, fp);
                Insert(line);
        }
}

in word.txt its just a bunch of words on each line i.e.

apple
banana
...
zoo

(... just means a bunch of words in between) it prints this:

word is apple
AFTER
word is banana
AFTER
...(a bunch more repetitions)                                    
word is cookie
Segmentation Fault(core dumped)

Why is there a segmentation fault? it printed the word perfectly. And it didn't print the AFTER

Thanks.

I don't think this is the error but why do you read up to 256 bytes into an array where you only have 28b? Change line[28] to line[256] and see if that helps. — Gille
– Gille, Commented Dec 3, 2012 at 7:06
char line[28]; then fgets(line, 256, fp); seems nasty. You can have a very nice solution for this. — user529758
– user529758, Commented Dec 3, 2012 at 7:06
That's what happens when you try to put 256 pounds of potatoes in a 28 pound bag. — Nik Bougalis
– Nik Bougalis, Commented Dec 3, 2012 at 7:10

Jeyaram · Accepted Answer · 2012-12-03 07:08:58Z

1

Allocated memory only 28 bytes where as trying to copy 256 byte.

char line[28]; <-- 28 bytes only allocated to line.
        while(!feof(fp)){
                fgets(line, 256, fp); <-- 256 bytes read into line.

Increase the memory for line to avoid this issue.

answered Dec 3, 2012 at 7:08

Jeyaram

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2 Comments

user529758 Over a year ago

please don't use duplicate constant sizes! I'd suggest using sizeof(line) instead.

AnT stands with Russia Over a year ago

@H2CO3: Please, don't clutter the code with superfluous parentheses. sizeof line is sufficient.

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