Segmentation Fault while assigning int to array

Question

I am try to read a line from a file, separate the chars, and then read them to a malloc'ed int array. I seem to be getting a segmentation fault when I use atoi to cast the char to an int, and thus I am unable to assign the int to the array. Any help would be appreciated.

int main(int argc, char * argv[]){

    FILE *in;
    in = fopen(argv[1], "r");
    FILE *out;
    out = fopen(argv[2], "w");

    int numDays;
    char ignore[256];
    fscanf(in, "%d", &numDays);
    fgets(ignore, sizeof(ignore), in);

    int *timeArray = (int *) malloc(numDays * sizeof(int)); ;

    char buffer[256];
    fgets(buffer, 256, in);

    const char delimiter[2] = " ";
    char *token;
    token = strtok(buffer, delimiter);
    int index = 0;
    while( token != NULL ) {
        printf( "%s\n", token);
        token = strtok(NULL, delimiter);
        int val = atoi(token);
        timeArray[index] = val;
        index++;
    }
    return(0);
}

Try using a debugger to see what's going wrong. e.g. is token a NULL at that time? — underscore_d

Nate Eldredge Nate Eldredge · Accepted Answer · 2021-02-04T17:43:10

When no tokens are left, strtok() returns NULL. But you call atoi(token) on it immediately, which will crash if it is NULL. The loop condition while (token != NULL) doesn't help because it isn't checked until the end of the loop body.

You need to restructure the loop so that the test is done before you try to use the result.

Segmentation Fault while assigning int to array

1 Answers