Segmentation faults are common run-time error for C programs. When we run the program we will get segmentation violation or segm4
entation fault or similar errors and the program exits. Segmentation faults generally observed inside weak or untested applications.

Common Causes Of Segmentation Faults

There may be a lot of different causes for Segmentation Faults but there are some common ones which creates most of them.

• Improper format control string in printf() and scanf() functions
• Forgetting use of & on the arguments in scanf() function
• Accessing beyond the bound of an array
• Failure to initialize a pointer before accessing it
• Incorrect usage of & address and * dereferencing operators

Segmentation Fault Examples

memset() Function

In this part we will examine segmentation faults. In the following code memset() function line will create a segmentation fault.

#include<stdio.h> 

int main(void) 
{ 
  memset((char *)0x0, 1, 100); 
  printf("HELLO POFTUT.COM \n"); 
  return 0; 
}

And when we try to execute this code binary we will see following line.

$ ./a.out  
Segmentation fault (core dumped)

Array Bound

In this case we will exceed the array bounds which will create a seg fault.

#include<stdio.h> 

int main(void) 
{ 
  int foo[1000]; for (int i = 0; i <= 1000 ; i++) foo[i] = i; 
  printf("HELLO POFTUT.COM \n"); 
  return 0; 
}

Illegal Memory Access

Illegal memory access is similar to the Array Bound situation.

#include<stdio.h> 

int main(void) 
{ 
  float *foo, *foo2; foo = (float*)malloc(1000); foo2[0] = 1.0; 
  printf("HELLO POFTUT.COM \n"); 
  return 0; 
}

Wrong scanf() Function Usage

scanf() function is used to input data from console. This input will use some pointers which can create segmentation fault if not used properly.

#include<stdio.h> 

int main(void) 
{ 
  int foo = 0; scanf("%d", foo); 
  printf("HELLO POFTUT.COM \n"); 
  return 0; 
}

Finding Problem Location by Debugging

The best and easy way to find a segmentation fault is using debugger. Debug information will provide more details about the problem and related code part.