CODEWITHSUNDEEP
csegmentation-faultvalgrindstrtokatoi
user2905147
user2905147

Reputation: 21

Invalid read of size 1

I am getting a segmentation fault when trying to run my program. After using valgrind these were my errors:

==32592== Invalid read of size 1
==32592==    at 0x3753637172: ____strtol_l_internal (strtol_l.c:298)
==32592==    by 0x3753633F1F: atoi (atoi.c:28)
==32592==    by 0x400B12: main (in /some/directory)
==32592==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

this is the loop which my problem definitely exists, but I cannot find where:

while( fgets(line, MAX_LEN, in) != NULL ) {
        ++linenum;
        token = strtok(line, " \n");
        if ( linenum == 1 ) {
            n = atoi(token);
            G = newGraph(n);
        }else {
            x = atoi(token);
            token = strtok(NULL, " \n");
            y = atoi(token);
            if( x != 0 ) {
                addArc(G, x, y);
            }
        }
    }

And this is an example of a text file I will be reading in:

9
1 2
2 1
2 3
3 5
5 4
4 3
5 6
6 8
7 6
8 7
8 9
1 3
1 4
1 5
1 6
1 7
1 8
1 9
2 4
2 5
2 6
2 7
2 8
2 9
3 6
3 7
3 8
3 9
4 6
4 7
4 8
4 9
5 7
5 8
5 9
6 9
7 9
9 9
0 0

Upvotes: 1

Views: 3560

Answers (2)

Rohan
Rohan

Reputation: 53366

strtok() can return NULL so check value of token before using it.

token = strtok(line, " \n");
if(token != NULLL)
{
        if ( linenum == 1 ) {
            n = atoi(token);
            G = newGraph(n);
        }else {
            x = atoi(token);
            token = strtok(NULL, " \n");
            if(token != NULL)
                y = atoi(token);
            if( x != 0 ) {
                addArc(G, x, y);
            }
  }

Upvotes: 2

alk
alk

Reputation: 70971

strtok() could very well return NULL, which is not a good idea to pass to atoi().

Upvotes: 2

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