CODEWITHSUNDEEP
csegmentation-fault
Faris McKay
Faris McKay

Reputation: 19

Why Does This Throw A Segmentation Fault?

Why is this throwing a segmentation fault? I am debugging it and have narrowed it down to the assignment of the masses in the switch statement, how am I supposed to go about doing that instead?

Here is my code:

#include <stdio.h>
#define MAX 100


struct cg {
    int x, y, mass;
};
struct cg masses[MAX];

int numberOfEntries;

int readin(void) {
    FILE *file;
    int massesRead, i, num, partRead = 0;
    file = fopen( "WeightData.txt", "r" );
    if( file == NULL ) {
        printf( "Error: can't open file.\n" );
        return 1;
    } else {
        while( fscanf( file, "%d", &num ) > 0) {
            switch(partRead){
                case 0:
                    masses[i].x = num;
                    partRead++;
                    continue;
                case 1:
                    masses[i].y = num;
                    partRead++;
                    continue;
                case 2:
                    masses[i].mass = num;
                    massesRead++;
                    partRead = 0;
                    i++;
                    continue;
            }
        }
    }
    fclose( file );
    numberOfEntries = massesRead;
    return massesRead;
}

void computecg(int n_masses) {
    int sum_of_xmass;
    int sum_of_ymass;
    int sum_of_mass;
    for(int i=0; i< numberOfEntries; i++){
        sum_of_xmass += (masses[i].x * masses[i].mass);
        sum_of_ymass += (masses[i].y * masses[i].mass);
        sum_of_mass += (masses[i].mass);
    }
    int cg_x = sum_of_xmass / sum_of_mass;
    int cg_y = sum_of_ymass / sum_of_mass;

    printf("X = %d Y = %d.",cg_x, cg_y);
}

int main() {
    int number;
    if((number = readin()) > 0){
        computecg(number);
    }
    return numberOfEntries;
}

Upvotes: 0

Views: 76

Answers (2)

Crowman
Crowman

Reputation: 25936

You write things like this:

masses[i].x = num;

but after:

int massesRead, i, num, partRead = 0;

you never assign a value to i, so most likely it is some huge garbage number that is way higher than 100, hence you go way out of bounds on your array and get your segfault.

You have a similar problem with never initializing massesRead, and then trying to do massesRead++;

To fix, you can change to:

int massesRead = 0, i = 0, num, partRead = 0;

Upvotes: 1

Felix Darvas
Felix Darvas

Reputation: 507

Very likely you assign more elements to masses than you defined. Print out your index i in the read routine and check, if it goes >100.

Upvotes: 0

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