Question

  char* output= (char*) argv[2];
 92     fp = fopen(output, "w");
 93     if( fp = NULL )
 94     {
 95         printf("writing output failed");
 96         return 0;
 97     }
 98     fprintf(fp,"hello");

This is causing seg fault exc bad memory at line 98.
What am I missing??

Answer 1

Line 93

if( fp = NULL )

is assigning fp to NULL rather than comparing it to NULL. Use

if( fp == NULL )

instead.

As netcoder pointed out, your compiler should warn you about this. You could also write your test in the form if (NULL == fp) to generate a compiler error if you accidentally swap comparison for assignment. (Note that some people may find this style of coding distasteful so it may generate some complaints in code reviews!)