Segmentation fault - Unknown reason

Question

I am getting segmentation fault with this code even though the two files are having 2^14 values each. Could anyone tell me the reason why.

#define N 128 #include<stdio.h> #include <malloc.h> int A[N][N]; int B[N][N]; int C[N][N]; void mmul(); int main() { int p,q; FILE *fp; fp=fopen("A.txt","r"); if(fp=NULL) printf("Error\n"); printf("A"); for(p=0;p<(1<<7);p++) { for(q=0;q<(1<<7);q++) { fscanf(fp, "%d", &A[p][q]); } } fclose(fp); fp=fopen("B.txt","r"); if(fp=NULL) printf("Error\n"); for(p=0;p<(1<<7);p++) { for(q=0;q<(1<<7);q++) { fscanf(fp, "%d", &B[p][q]); } } fclose(fp); printf("here"); mmul(); } void mmul() { int i,j,k; unsigned int sum; for(i=0;i<N;i++) { for(j=0;j<N;j++) { sum=0; for(k=0;k<N;k++) { sum=sum+(A[i][k]*B[k][j]); } C[i][j]=sum; } } }

If you run this under your platform debugger (gdb, whatever) you will likely be told immediately what is causing the seg-fault, which from this code is likely the only thing that is referencing a raw pointer: the FILE *fp and your assignment, rather than evaluation-check, to NULL. — WhozCraig
– WhozCraig, Commented Nov 9, 2012 at 16:31
-1 I just peeked 3 random questions that are marked as related, and found in all of them suggestions to use a debugger or run through valgrind. This clearly indicate that you didn't look around that much. — Massimiliano
– Massimiliano, Commented Nov 9, 2012 at 16:35

David Ranieri · Accepted Answer · 2012-11-09 16:30:44Z

8

Compile with warnings

if (fp = NULL)

answered Nov 9, 2012 at 16:30

David Ranieri

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Comments

Dmytro Sirenko · Accepted Answer · 2012-11-09 16:34:07Z

if(fp=NULL) printf("Error\n");`

it is the whole if body. So if there is no file, you'll get a NULL fp, print "Error" and continue the execution with NULL fp. It causes the segmentation faults.

Also, it is an assignment, not a comparison, so you always get NULL fp, not printing the error.

You need to add exit statement:

if (fp == NULL) { fprintf(stderr, "Error: failed to open file\n"); return -1; }

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