Real-world examples of segmentation fault examples: common runtime errors

Let’s start with concrete failures. These are not contrived textbook puzzles; they’re examples of segmentation fault examples: common runtime errors that show up in interviews, bug trackers, and production outages.

Example of out-of-bounds array access

A classic example of segmentation fault behavior is reading or writing beyond the bounds of an array. In C:

#include <stdio.h>

int main(void) {
    int arr[3] = {1, 2, 3};

    // Bug: index 3 is out of bounds (valid: 0, 1, 2)
    printf("%d\n", arr[3]);

    return 0;
}

On some platforms this prints garbage; on others it triggers a segmentation fault. Either way, this is undefined behavior. The CPU is trying to read memory that the process either doesn’t own or isn’t allowed to access.

This is one of the best examples of segmentation fault examples: common runtime errors because it looks harmless. The code compiles cleanly, passes basic tests, and then randomly explodes in production when that out-of-bounds access happens to touch protected memory.

How to fix it:

• Track array length explicitly
• Validate indices before access
• Prefer safer abstractions (e.g., std::vector::at() in C++ or bounds-checked containers)

Null pointer dereference: the everyday offender

Another everyday example of segmentation fault examples: common runtime errors is dereferencing a null pointer. This one is so common that many engineers almost tune it out—until it takes down a service.

#include <stdio.h>

int main(void) {
    int *ptr = NULL;

    // Bug: dereferencing NULL
    printf("%d\n", *ptr);
    return 0;
}

Most modern OSes map the null page as non-accessible. When the CPU tries to read or write through ptr, the kernel sends a signal (like SIGSEGV on Linux), and your process dies.

Real-world pattern:

• Function returns NULL on error
• Caller “knows” it can’t fail and skips the check
• Edge case in production triggers the error path
• Suddenly you have a segmentation fault in the logs

In 2024, static analysis tools and linters are good at warning about potential null dereferences, but they’re not perfect. You still see this in C/C++ projects, embedded firmware, and even some high-performance Rust code that uses unsafe blocks.

Use-after-free: accessing memory that used to be yours

Use-after-free bugs are some of the nastiest examples of segmentation fault examples: common runtime errors, because they often look fine under light testing and then fail only under load.

#include <stdlib.h>
#include <stdio.h>

int main(void) {
    int *data = malloc(sizeof(int));

    *data = 42;

    free(data);      // Memory returned to allocator

    // Bug: use-after-free
    printf("%d\n", *data);

    return 0;
}

After free, data is a dangling pointer. The memory might be reused for something else or unmapped entirely. Reading through it might:

• Seem to “work” in a debug run
• Print a random value
• Crash with a segmentation fault in production

In security terms, use-after-free is more than just a runtime error; it’s a common exploit vector. The MITRE CWE-416 entry documents how attackers can use this pattern to hijack control flow.

Mitigation patterns:

• Set pointers to NULL immediately after free
• Use ownership models (std::unique_ptr in C++, Rust’s ownership system)
• Run with AddressSanitizer (-fsanitize=address) in CI to catch these examples of segmentation fault errors early

Stack overflow from runaway recursion

Not all segmentation faults come from wild pointers. A surprisingly common example of segmentation fault examples: common runtime errors is blowing the stack with deep or unbounded recursion.

#include <stdio.h>

void recurse_forever(int n) {
    int buffer[1000]; // Uses some stack space
    printf("Depth: %d\n", n);
    recurse_forever(n + 1);
}

int main(void) {
    recurse_forever(1);
    return 0;
}

Eventually, the stack pointer runs into a guard page. The next function call tries to write a new frame into protected memory, the OS raises a fault, and your process dies.

Where this shows up in real life:

• Incorrect base case in recursive algorithms
• Mutual recursion between two or more functions
• Servers processing deeply nested data (e.g., JSON, XML) without depth limits

On Linux, you can inspect and adjust stack limits with ulimit -s. The GNU C Library manual has more detail on stack behavior and signals.

Buffer overflow in C strings

C strings are another rich source of examples of segmentation fault examples: common runtime errors. A classic pattern is writing past the end of a fixed-size buffer.

#include <string.h>
#include <stdio.h>

int main(void) {
    char buf[8];

    // Bug: copies 20 bytes into an 8-byte buffer
    strcpy(buf, "this is too long");

    printf("%s\n", buf);
    return 0;
}

This can corrupt adjacent stack data, including the saved return address. Sometimes it “just” crashes with a segmentation fault; other times it becomes a security vulnerability. The CERT C Coding Standard from Carnegie Mellon University documents safer patterns and functions.

Safer alternatives include strncpy, snprintf, and higher-level string types in C++ or other languages. But the core lesson is the same: always track buffer sizes and never assume input will fit.

Dangling pointers from returning stack addresses

Here’s a subtle example of segmentation fault examples: common runtime errors that often shows up in interview questions and real code written under time pressure.

#include <stdio.h>

int *get_number(void) {
    int x = 10;
    return &x; // Bug: returning address of a local variable
}

int main(void) {
    int *ptr = get_number();
    // Stack frame of get_number is gone; ptr is dangling
    printf("%d\n", *ptr); // May crash
    return 0;
}

x lives on the stack. Once get_number returns, that stack frame is invalid. The pointer ptr now points to memory that can be reused for anything else. Reading through it is undefined behavior and can easily cause a segmentation fault.

Safer alternatives:

• Return by value (int get_number(void) { return 10; })
• Allocate on the heap and document ownership
• Use smart pointers in C++ to express lifetime

Misaligned or invalid pointer arithmetic

Low-level pointer arithmetic can also trigger examples of segmentation fault examples: common runtime errors, especially when mixing types or casting from integers.

#include <stdio.h>

int main(void) {
    char *p = (char *)0x1; // Almost certainly invalid address
    printf("%d\n", *p);   // Bug: access invalid memory
    return 0;
}

This is an extreme example, but milder versions show up when:

• Casting integers to pointers from serialized data
• Doing manual memory pool management
• Miscalculating offsets in packed structs or network protocols

Modern compilers and sanitizers help, but they can’t save you from every bad pointer cast. Treat raw pointer arithmetic as a power tool: only when necessary, with careful reasoning.

Concurrency and race conditions leading to segfaults

With more code running on multi-core systems and in microservices, data races have become a modern source of segmentation fault runtime errors. Consider two threads sharing a pointer:

// Pseudo-code, not complete

int *shared_ptr;

void writer_thread(void) {
    shared_ptr = malloc(sizeof(int));

    *shared_ptr = 123;
    free(shared_ptr); // Bug: no synchronization
}

void reader_thread(void) {
    if (shared_ptr != NULL) {
        // Race: shared_ptr may have been freed
        printf("%d\n", *shared_ptr); // Possible use-after-free
    }
}

Depending on timing, the reader thread might dereference a freed pointer and crash. These are some of the hardest examples of segmentation fault examples: common runtime errors to debug, because adding logging changes timing and can “hide” the bug.

Tools like ThreadSanitizer (-fsanitize=thread) and data race detectors in modern IDEs are increasingly used in 2024–2025 to catch these issues earlier in development.

Why segmentation faults happen: the short version

All of these examples of segmentation fault examples: common runtime errors share a single core idea: your process tried to touch memory it shouldn’t.

Under the hood:

• The OS gives each process a virtual address space
• Some regions are readable/writable, some are off-limits
• When the CPU hits an invalid access, the OS sends a signal (e.g., SIGSEGV)

Languages like C and C++ give you direct control over memory, which is powerful but error-prone. Managed languages (Java, C#, Python, JavaScript) typically throw exceptions instead of segfaulting, but they can still crash if native extensions or unsafe code misbehave.

For a deeper systems-level description, the Linux man-pages project documents SIGSEGV and related signals.

Modern debugging strategies for segmentation fault runtime errors

In 2024–2025, debugging examples of segmentation fault examples: common runtime errors is less about staring at code and more about using the right tools.

Use a debugger: gdb or lldb

Run your program under a debugger:

gdb ./my_program
(gdb) run
## wait for segfault
(gdb) bt   # backtrace
(gdb) frame 0
(gdb) info locals

You get:

• Exact line where the segmentation fault occurred
• Call stack leading to the crash
• Local variable values

On macOS, lldb plays a similar role.

Enable sanitizers in CI

AddressSanitizer and friends are now standard in many serious C/C++ codebases:

gcc -g -O1 -fsanitize=address -fno-omit-frame-pointer main.c -o main
./main

Instead of a vague “Segmentation fault,” you’ll often see a detailed report:

• Type of error (heap-buffer-overflow, stack-use-after-return, etc.)
• Exact source line
• Shadow memory state

This turns many examples of segmentation fault examples: common runtime errors into straightforward fixes.

Add guardrails in APIs and coding standards

Teams that write low-level code and care about reliability typically:

• Ban raw new/delete in C++ in favor of RAII and smart pointers
• Require bounds-checked accessors for containers
• Use code review checklists that explicitly look for pointer lifetime issues
• Integrate static analyzers like clang-tidy or commercial tools

Organizations like CERT at Carnegie Mellon maintain secure coding guidelines that are worth bookmarking, especially if you work on safety-critical systems.

2024–2025 trends: fewer segfaults, more tooling

The industry is slowly moving away from raw memory-unsafe languages for new projects. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) and other organizations have been advocating for memory-safe languages in critical software. While this doesn’t eliminate all examples of segmentation fault examples: common runtime errors, it does shift them into narrower domains:

• Performance-critical components (databases, game engines, browsers)
• OS kernels and drivers
• Embedded and IoT firmware

Meanwhile, toolchains keep improving:

• Sanitizers are easier to enable and cheaper to run
• IDEs surface static analysis warnings inline
• CI systems routinely run tests with sanitizers and fuzzers

So while segmentation faults are not going away, the bar for shipping them to production is getting higher.

FAQ: examples of segmentation fault examples and quick answers

Q: What are some common examples of segmentation fault examples: common runtime errors in C and C++?
Typical examples include:

• Out-of-bounds array or buffer access
• Null pointer dereference
• Use-after-free and double-free
• Returning pointers to local stack variables
• Stack overflow from deep recursion
• Data races on shared pointers in multithreaded code

Q: Can high-level languages have any example of segmentation fault behavior?
Yes, but usually only when native extensions are involved. Python, Java, and C# code written purely in the language typically throws exceptions instead. However, a buggy C extension for Python, or a JNI call in Java, can still trigger a segmentation fault underneath.

Q: How can I quickly find the line that caused a segmentation fault?
Compile with debug symbols (-g), run under gdb or lldb, and inspect the backtrace when it crashes. For many examples of segmentation fault examples: common runtime errors, this immediately points you to the offending pointer or buffer.

Q: What is a good example of preventing segmentation faults in new code?
A solid example is using RAII and smart pointers in modern C++ instead of raw new/delete, plus containers like std::vector and std::string instead of manual arrays and C strings. Combined with AddressSanitizer in your test pipeline, this avoids a large class of segmentation fault runtime errors.

Q: Are segmentation faults always security vulnerabilities?
No. Some examples of segmentation fault runtime errors are just plain bugs with no obvious exploit path. However, patterns like buffer overflows and use-after-free are strongly associated with exploitable vulnerabilities, so they should be treated as high-priority issues.

If you treat these examples of segmentation fault examples: common runtime errors as a checklist when you debug—arrays, null pointers, lifetimes, recursion depth, concurrency—you’ll usually find the root cause faster than staring at the code in frustration.