Port ub.md

wiki/resources/general/ub.md

@@ -0,0 +1,87 @@
+---
+alias: ub
+bot_article: |
+  # Undefined Behavior
+
+  Undefined behavior (UB) is behavior for which the C/C++ standard imposes no requirements.
+
+  Typical causes are: reading uninitialized memory,
+  out-of-bounds memory access,
+  or using an object when it no longer exists.
+
+  ## Why it Matters
+
+  Compilers are not required to give warnings or errors for undefined behaviors and having them in your code can lead to
+  non-portable code, strange bugs and security vulnerabilities.
+---
+
+# Undefined Behavior
+
+Undefined Behavior is behavior for which the C/C++ standard imposes no requirements. <br/> In other words, the program
+can crash, continue or have different behaviors on different platforms. <br/> Here is an example of a UB:
+
+```cpp
+#include <iostream>
+
+int main() {
+    int a;
+    // UB in C and pre-C++26: uninitialized memory access
+    if (a >= 0) { // [!code warning]
+        std::cout << "non negative" << std::endl;
+    } else {
+        std::cout << "negative" << std::endl;
+    }
+    return 0;
+}
+```
+
+Uninitialized memory has what is called indeterminate values, values which are unspecified. The actual value of `a`
+depends on the platform and the compiler.
+
+## Why it Matters?
+
+Compilers are not required to give warnings or errors for undefined behaviors and having them in your code can lead to
+non-portable behaviors, strange bugs and security vulnerabilities.
+
+## Common UBs
+
+- **Signed integer overflow**
+
+  ```cpp
+  int x = INT_MAX;
+  // UB
+  int y = x + 1; // [!code warning]
+  ```
+
+  ::: info
+
+  Unsigned integer overflow is defined. `UINT_MAX + 1 == 0` is true.
+
+  :::
+
+- **Out-of-bound access**
+
+  ```cpp
+  int a[5] = {1,2,3,4,5};
+  // UB
+  int x = a[5]; // [!code warning]
+  ```
+
+- **Uninitialized memory access**
+
+  ```cpp
+  int x;
+  // UB pre-C++26
+  int y = x; // [!code warning]
+  ```
+
+  ::: info
+
+  Since **C++26**: this is classified as _erroneous behavior_, not _undefined behavior_.
+
+  :::
+
+## See also
+
+- [Undefined behavior C (cppreference)](https://en.cppreference.com/c/language/behavior)
+- [Undefined behavior C++ (cppreference)](https://en.cppreference.com/cpp/language/ub)

wiki/resources/sidebar.ts

@@ -48,6 +48,7 @@ const sidebar = [
                 items: [
                     { text: "Address Sanitizer", link: "/resources/general/asan" },
                     { text: "Ownership", link: "/resources/general/ownership" },
+                    { text: "Undefined Behavior", link: "/resources/general/ub" },
                     { text: "Standards", link: "/resources/general/standards" },
                     { text: "Project Ideas", link: "/resources/general/project-ideas" },
                     { text: "Floating Point Numbers", link: "/resources/general/floating-point" },