Segmentation fault in Linux

Examples

There are several examples that show the occurrence of segmentation fault.

Example 1:

The following example shows segmentation fault caused due to writing in read-only memory.

int main(void)
{
    char *str = "Hello World!";
    *str = 'H';
}

When you execute this code it will produce the runtime error on a Unix or Linux system. On debugging this code you will see –

Program received signal SIGSEGV, Segmentation fault.
0x1c0005c2 in main () at ex1.c:6
6               *str = 'H';

This code can be corrected by using an array instead of using a character pointer.

Example 2:

This example shows the segmentation fault caused due to boundary conditions in the array.

// Array out of bound error
int arr[100];
for (int i = 0; i <= 100 ; i++)
arr[i] = i;

Here arr is defined for index from 0 to 99. However, in the last iteration of the for loop, the program tries to access arr[100]. This will result in a segment fault if the memory location lies outside the memory segment where arr resides.

Causes of segmentation fault

Some typical causes of segmentation faults are –

• Program attempt to access memory that doesn’t exist
• Trying to access memory the program doesn’t have the right to
• Attempting to write read-only memory such as code segments
• Incorrect pointer manipulation
• Boundary condition errors
• Invalid assumptions about shared libraries
• You are attempting to execute a program that does not compile correctly