What is segmentation fault?

general
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1

When programming in c++ I often encounter segmentation fault.

What is it and how to debug it?

Regards,
Megh Parikh

2

When your program runs, it has access to certain portions of memory. First, you have local variables in each of your functions; these are stored in the stack. Second, you may have some memory, allocated during runtime (using either malloc, in C, or new, in C++), stored on the heap (you may also hear it called the “free store”).Your program is only allowed to touch memory that belongs to it – the memory previously mentioned. Any access outside that area will cause a segmentation fault. Segmentation faults are commonly referred to as segfaults.
It occur when you write -

 scanf("%d",n)

But right code is

 scanf("%d",&n);

When you declare size of array is 10 and in main program you will use more than array size .

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3

Looks like most of my errors are caused by local variables for I donot use any thing else. Do you know of any other reasons? I have a practoce of declaring each variable as global, so I think that there must be some other reason.(I encountered this error in last year codejam many times)

4

Segmentation fault occurs for various reasons.
Few are

  • Declaring local array or string which use large memory.
  • Stack Overflow generally due to large recursions
  • Dereferencing a pointer
  • Accessing a memory location not declared .

EX:- int arr[100],x=-1; cout<<arr[x];//segmentation error x=101; cout<<arr[i];//Segmentation error as program is trying to access memory out of bounds
Source: http://en.wikipedia.org/wiki/Segmentation_fault#Causes

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5

Thanks, now I understand the reason as sometimes I use excessive recursion. What is limit for recursion?

6

I think that depends on the memory being used by your recursion.
Ex:- If you pass a 10^5 array during each level of recursion you can calculate your max recursion level depending on the memory given by the compiler.

7

A segmentation fault occurs when a program attempts to access a memory location that it is not allowed to access, or attempts to access a memory location in a way that is not allowed (for example, attempting to write to a read-only location, or to overwrite part of the operating system).