Crashing Barriers: A Journey Through Segmentation Fault

Segmentation fault in programming is related to the memory segments. While programming, it is necessary to divide the memory into various segments like code, stack, and heap. However, the allocated memory for each segment is restricted. It means a program can only access the memory of that segment if it has access to it. Otherwise, an error or fault will occur if the program cannot access the memory and still tries to access it. This fault in programming is called the segmentation fault.

Segmentation can occur for multiple reasons, such as stack overflow, dereferencing a null pointer, etc. These reasons can be defined as the type of segmentation fault. Moreover, types of segmentation fault in programming depends upon the programming language.

So, in this blog post, you can learn about the reasons and common segmentation fault in C, one of the most popular programming languages.

Reasons for Segmentation Fault in C

Segmentation faults in C and C++ are commonly caused when a program:

Attempts to access a memory that is not allocated to it.

Attempts to access a memory that is not valid.

Attempts to access a read-only memory for writing purposes.

These three are the most common causes of segmentation in C. Based on these reasons, there can be many segmentation errors, such as stack overflow, buffer overflow, null pointer dereferencing, etc. Here's an overview of some common segmentation faults in C and their respective causes.

Common Segmentation Fault in C

Buffer Overflow

While programming in C, you may encounter this segmentation error while working on a buffer. A buffer is a memory with a fixed size. A buffer overflow occurs when a program tries to write data in its allocated memory (buffer), which is more than the size of the memory.

So, when the buffer gets full, the program attempts to access the neighboring memory locations. But since the program is not allowed to access these locations, it results in a segmentation fault that can cause code crashes, data corruption, and even security issues.

Example of Buffer Overflow

In this program, the 'copyString()' function has to copy an input "Hello, world!" 13 characters long into a buffer of size limit 8.

So, when it attempts to do so, it will result in a buffer overflow segmentation fault in C.

Prevention of Buffer Overflow

Buffer overflow can be prevented if:

You allocate the proper size to the buffer, which should be enough for the length of the input.

You check the buffer capacity before executing the program.

You avoid the manual allocation of the memory. Instead, you can use higher-level constructs and libraries for memory allocation and management.

These few tips can help you to save yourself from buffer overflow segmentation fault in C.

Stack Overflow

Stack overflow is another common segmentation fault in C. A data structure in a program called "call stack" is responsible for managing function calls and local variables. When the call stack in the program exceeds the allocated limit, the program crashes or shows unexpected behavior.

Stack Overflow Example

In the above example, the program has a "recursive function" and a "local variable." But, the recursive function in the above code is set to recall itself repeatedly till "n." Now, since "n" is not a finite limit, it will lead to Infinite recursions of the "recursive function." Moreover, once the allocated memory for the recursion of the "recursive function" is filled, it will overflow the call stack and result in a stack overflow segmentation fault in C.

Prevention of Stack Overflow

Stack overflow can be prevented if:

You put a termination condition to ensure that the recursion will stop and not overflow the allocated memory.

You efficiently allocate the space for the recursive function to complete it within the memory limit.

Null Pointer Dereferencing

A null pointer in C refers to a pointer that is ultimately pointing towards nothing. But when this null pointer is dereferenced to point towards an invalid memory space, then it causes a segmentation fault in C called null pointer dereferencing.

Example of Null Pointer Dereferencing

The above example has a null pointer, "ptr." It is a null pointer because it is assigned equal to null. However, in the next line of code, the "ptr" is attempted to be assigned to "10," which is an error as "ptr" has no memory to comply with. This condition will result in a segmentation fault in C called null pointer dereferencing.

Prevention of Null Pointer Dereferencing

Null pointer dereferencing can be prevented if:

You properly initialize the pointers by either allocating them to memory or assigning them to null.

You check whether the null pointer is valid before dereferencing it to a new value.

You use debugging tools such as GDB to check for any null pointer dereferences in the code. Moreover, you can do C programming in VS code editor.

Writing in Read-Only Memory

As you can guess by the name, in this segmentation fault in C, the program attempts to write something in a memory that is dedicated to read-only purposes. It can cause memory access violations in the program and can even lead to code crashes.

Example of Writing in Read-Only Memory

Here, you can see a character pointer "str" exists, which says, "Hello, world." String literals, which are "Hello, world," typically utilize a read-only space. So when the next line of the program attempts to edit the first letter of the string literal from 'H' to 'h,' the program will face a segmentation fault in C. This fault is known as writing in read-only memory.

Prevention of Writing in Read-Only Memory

Writing in read-only memory can be prevented if:

You properly allocate the right memory to the pointer. If you intend to make changes in the string, then use writeable memory.

You enable warnings in your compiler.

You can do C programming in VS code.

Conclusion

Segmentation faults in programming can cause problems for you and your project. It is necessary to practice the prevention of segmentation faults in programming to run your code flawlessly. In addition to practice, you can do C programming in VS code editor or use debuggers like GDB to ensure error-free code execution. Moreover, rechecking your code is also necessary before its execution, as it will make you better at programming.